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Pope Weather

Forecast Reference Notebook (FRN)

02 March 2007

Pope AFB FRN INDEX

SECTION

Section 1: Site Information:

Section 1a: Installation Information:

Section 1b: Geography/Topography:

Section 1c: Meteorological Instrumentation:

Section 1d: Units Supported:

Section 1e: Aircraft Supported:

Section 2: Local Aircraft/Ground Force Weather Sensitivities and Impacts:

Section 3: Climatology and Seasonal Controls:

Section 4: Synoptic/Mesoscale Weather Regimes:

Section 5: Forecast Techniques/Rules of Thumb:

Section 6: Forecast Studies and Research:

Section 7: Contingency/Exercise Areas:

Section 8: Miscellaneous Information:

Section 1: Site Information:

Section 1a: Installation Information:

Pope Air Force Base (AFB) is located in south central North Carolina in the extreme western part of the southern coastal plain in an area called the Sandhills. It is on the northeastern part of Ft. Bragg, approximately 2 miles northeast of the main post area. Fayetteville is the largest nearby city and is approximately 10 miles southeast of the base (see Figure 1). Other large cities near Pope AFB are:

Town Distance Direction Raleigh/Durham/Chapel Hill, NC 50 mi N Wilmington, NC 80 mi SE Charlotte, NC 85 mi W Greensboro/High Point/Winston Salem, NC 75 mi NW

Other airfields near Pope AFB are:

Airfield (WMO Identifier) Distance Direction Raleigh-Durham International (RDU) 50 mi N Seymour-Johnson AFB (GSB) 50 mi ENE Simmons AAF (FBG) 5 mi ESE Fayetteville Regional (FAY) 12 mi SSE Florence Regional (FLO) 70 mi SW Mackall AAF (HFF) 25 mi SW Charlotte International (CLT) 90 mi W Piedmont Triad International (GSO) 70 mi NW

Coordinates of the airfield are: 35°10.2’N and 79°00.9’W and the field elevation is 217 feet MSL. The Base Weather Station is located about 300 yards west of the 23 end of the main runway in building 708 which also houses Base Operations. Within the weather station are the readouts from the meteorological sensors of the dually instrumented main runway. Official observing site is the FMQ-19 sensors at both end of the runway. As a back-up, manual surface observations are taken from a point about 150 feet away from the southwest side of building 708. This point has a limited field of view due to the hangars in the area. Unobstructed view ranges from 100-260° and 280-

330°. The horizon is blocked at all angles due to tree lines, buildings, and hangars. These obstructions don’t allow the observer to see the approach end of runway 23.

Figure 1

Section 1b: Geography/Topography:

Regional North Carolina is divided into three major regions: the Coastal Plain, the Piedmont, and the Appalachian Mountains (see Figures 2 and 3 below). The Coastal Plain runs from the Atlantic coast inland to about 50 miles west of Pope AFB and runs southwest to northeast through North Carolina. The ground is generally sand and the vegetation is mainly pine and fir trees. The Coastal Plain and the Piedmont are separated by a line called the “fall line” which causes a gradual rise in terrain of several hundreds of feet near this transition zone. Piedmont literally means of, or formed, at the bottom of mountains. So, the Piedmont is the transition zone between the Coastal Plain and the Appalachians. The Piedmont is made up of mostly sand in the eastern edge and transitions into more rock/soil composition in the western edge. Vegetation ranges from

pine and fir in the east to oak and maple in the west. In the western quarter of the state lies the Appalachian Mountains. Here, the ground is mainly soil/rock and the vegetation is mainly oak and fir trees.

Figure 2

Relief Map

Atlantic Ocean

Figure 3

Off the coast of North Carolina lies the Atlantic Ocean. Distances range from as close as 85 miles to the southeast and as far as 140 miles to the northeast. Flow off the ocean is a primary source of moisture for Pope AFB.

Another source of moisture for the local area is the Gulf of Mexico which lies about 460 miles to the southwest of Pope AFB. During periods of extended southwesterly flow, the Gulf exhibits a significant influence on our weather.

West-southwest through north-northwest at a distance of 130-160 miles of the airfield lie the Appalachians. These mountains range in elevation from 1,500 to more than 6,000 feet, and, like the Atlantic Ocean and the Gulf of Mexico, they have a considerable impact on the weather affecting this area.

Section 1c: Meteorological Instrumentation:

1. Runway Orientation and Lengths: The Pope AFB runway is oriented northeast- southwest (050-230) with the primary runway being runway 23. The runway is 7,501 feet long and 150 feet wide with 1,000 foot over-runs on each end. Runway 23 has dual meteorological instrumentation for all reported elements. In addition to the primary runway, there is a paved assault strip southeast of, and parallel to, the runway with a grass median separating them that is about 40 feet wide. This assault strip is 3,000 feet long by 60 feet wide and has no over-runs (see Figure 4 below).

Pope AFB Airfield Diagram Field Elevation 217’

Weather Equipment Layout

FMQ 19 23 FDCU

FMQ 19 05 FDCU

Manual Observing Site

Figure 4

2. Meteorological Sensors and Their Locations:

a. OPERATIONAL PRINCIPLE USER PROCESSOR (OPUP): Actual OPUP dish site is 43 miles NNE of Pope AFB and belongs to the National Weather Service at Raleigh, NC. Our user terminal (or Operational Principal User Processor (OPUP)) is located in the Base Weather Station.

b. FMQ-19: One of these sensors is at each end of the runway. At the 23 end, the sensor sits about 150 feet to the east of the runway in the infield grass area. The 05 end sensor sits about 150 feet to the west of the runway in the infield grass area. These units sit 10 feet off of the ground

Section 1d: Units Supported:

1. 43d Airlift Wing 2. 23d Fighter Group 3. 427th Special Operations Squadron 4. U. S. Army Golden Knights

Section 1e: Aircraft Supported:

1. C-130 2. A-10 3. BE-20 4. DHC-6 5. PC-6 6. CN-235 7. C-208 8. C-31 9. UV-20

(Aircraft 3-9 belongs to the 427th Special Operations Squadron, and the Golden Knights. The A-10 airframe is very sensitive to hail, but the main factor for weather is the proficiency of the A-10 pilot. Weather affects each pilot differently.

Section 2: Local Aircraft/Ground Force Weather Sensitivities and Impacts:

The weather impacts on aviation and non-aviation assets at Pope AFB are listed in Table 1.

Table 1. Weather Impacts on Aviation and Non-Aviation Assets at Pope AFB

Weather Lead Impact Customer Action Phenomena Time Tornado 30 min Personal injury Seek shelter; hangar or divert Equipment damage aircraft Hail 1/2” but less 90 min Personal injury Seek shelter; hangar or divert than 3/4” Equipment damage aircraft Hail 3/4” or more 120 min Personal injury Seek shelter; hangar or divert Equipment damage aircraft Freezing Precipitation 90 min Delay or cease Cease flying; hangar or protect operations aircraft Surface winds over 120 min Flight hazard Cease unnecessary flying; 50kts Equipment damage secure or hangar aircraft; secure light objects outside Surface winds 35- 90 min Flight hazard Cease unnecessary flying; 49kts Equipment damage secure or hangar aircraft Surface winds 20kts Observed Personnel hazard Cease wing walking on large or more aircraft Snow 2” or more in 90 min Aircraft landing and Implement snow removal 12 hours takeoff/base roads affected Thunderstorms/Light Observed Flight hazard Caution (C-130) ning within 10 NM Stop Refueling (A-10) Severe Observed Flight hazard Caution Thunderstorms within 25 NM Lightning w/in 5 NM Observed Delay operations Cease flight-line work. Clear of Pope AFB pool/golf course Icing / Turbulence Observed Flight hazard A-10s won’t fly with observed moderate or greater icing/turbulence C-130s won’t fly with observed severe icing/ turbulence C-130 (restricted) observed moderate or greater turbulence Low Level Wind Observed Flight hazard Caution Shear

Fighter Index of Observed Personnel hazard Limits pilot time in cockpit on Thermal Stress ramp Danger Heat Stress Index V Observed Personnel hazard Work/rest cycle on flight-line Ceiling/visibility <200 Observed Airfield minimums Runway closed for takeoff and / 1/2 landings Crosswind ≥ 15 kts Observed Flight hazard A-10s can’t do formation takeoffs C-130s need to watch aircraft weight Winds 13kts N/A Limit for personnel Monitor winds jumps Winds 17kts N/A Limit for HALO jumps Monitor winds Sustained Winds Observed Personnel hazard Stop C-130 fuel tank ≥ 15 kts maintenance

Section 3: Climatology and Seasonal Controls

1. Synoptic Climatology

(a). MAJOR CONTROLLING FEATURES. The only significant synoptic feature that has a controlling affect on Pope AFB is the Bermuda High. During the summer, this semi-permanent feature resides off the east coast and tends to give North Carolina favorable flying conditions. Summer does bring a greater chance of thunderstorms, but since they are usually of the “air mass” type they don’t usually hamper operations for very long. Since this feature is a warm barotropic high, it migrates from about 30N to 30S with the seasons. Therefore, when winter comes, it is well to the south and no longer dominates our weather.

(b) AREAS OF CYCLOGENISIS: Frontal lows affecting Pope AFB can form at any point along a frontal boundary where conditions are conducive for formation. Very frequently, however, major frontal lows will follow similar patterns of development in the same general area due to terrain or oceanic influences. The categorization of lows affecting Pope AFB is based on the general area of the low formation or intensification. Figure 5 below shows the major areas where cyclogenisis affecting Pope AFB occurs. These include the Alberta Clipper, the Northern Rockies Low, the Colorado Low, the West Texas Low, the Gulf Low, the South Atlantic Low, and the Hatteras Low.

Figure 5

(c) AREAS OF ANTI-CYCLOGENISIS: As with areas of cyclogenisis, major anticyclones can occur at any point where conditions are favorable. Experience and objective data show that a majority of persistent major migratory anticyclones affecting Pope AFB originate over the North Pacific, northwestern U.S., western Canada, over

the Great Plains, or over the area east of the Mississippi River. Figure 6 below shows the major areas where anti-cyclogenisis affecting Pope AFB originate.

Figure 6

2. Synoptic Weather

a. WINTER:

(1) Winter Air Masses And Associated Weather: Continental polar, maritime polar, and maritime tropical along with their modified versions are the primary air masses that affect Pope AFB in the winter. Occasionally, Pope AFB may see an arctic outbreak, but this air mass is usually well modified by the time it reaches North Carolina. Frontal passage signifies a change in air mass and depending on the type of the two air masses colliding, Pope AFB can experience varying weather.

(a) Continental Polar (cP): This is the most common type of air mass seen in the winter. Its source region is the Canadian interior, and until later in the winter, we only see the modified continental polar air mass. When cP air moves in behind a front, the cold dry air and downward vertical motions associated with it cause a rapid clearing of the frontal clouds. The cP air can move in to our area from the southwest through the northeast. With high pressure building in after frontal passage, Pope AFB usually sees a day or two of strong, gusty winds that veer from northwest with time. Skies usually stay clear to widely scattered for the first few days after frontal passage with the skies becoming more cloudy in response to the next front nearing Pope AFB. The usual period between fronts is about four days. With cP air, Pope AFB experiences minimum temperatures around freezing with an occasional low in the single digits. The relative humidity is also low due to the low moisture content of cP air. Precipitation associated

with cP air can be liquid, freezing, or frozen in type. Thunderstorms in the winter are rare and usually associated with fast moving cold fronts as the cP air collides with warmer, more moist, maritime tropical air.

(b) Maritime Tropical (mT): The mT air affecting Pope AFB has two primary source regions: the Gulf of Mexico and the Atlantic Ocean. This air mass usually follows a warm frontal passage of either the looping warm front (Figure 7) or coastal warm front variety and it brings widespread stratus and fog to our area. The mT air can reach Pope AFB from the northeast through the southwest. Due to the high moisture content and warmth of the air, mT air can cause low ceilings, visibilities, and precipitation to persist until frontal passage. This air mass modifies and tempers the Pope AFB weather all year and has even caused winter temperatures into the 80s. Precipitation associated with mT air usually changes from snow to freezing rain then to rain as the warm front pushes north. Thunderstorms occur at the boundary of mT and cP air before frontal passage (an active front) with air mass thunderstorms being an unlikely event.

LOOPING WARM FRONT H H

Figure 7

Maritime tropical air is in unmodified form when it reaches the southern portion of the United States. Temperature and moisture content are higher in this air mass than in any other American air mass in winter. In the southern states along the Atlantic coast and Gulf of Mexico, mild temperatures and high humidities with much cloudiness are found, especially during the night and early morning. This is the characteristic weather found in mT air in the absence of frontal conditions. The stratus- and stratocumulus-type clouds that form at night tend to dissipate during the middle of the day, and fair weather is then the rule. Visibility is generally poor when the cloudiness is present; however, it improves rapidly because of convective activity when the stratus clouds dissipate. The ceilings associated with the stratus condition are generally on the order of 500 to 1,500 ft, and the tops are usually not higher than 3,500 to 4,500 ft. The tops of the clouds usually coincide with the temperature inversion. Precipitation does not occur in the absence of frontal action. With frontal activity, the convective instability inherent in this air is

released, producing copious precipitation. Occasionally when land has been cooled along the coastal area in winter, maritime tropical air flowing inland will produce an advection fog over extensive areas.

In general, flying conditions within this air mass are fair. Ceilings and visibilities are occasionally below safe operating limits however, flying conditions are relatively smooth, and icing conditions are absent near the surface layers. As the trajectory carries the mT current northward over progressively colder ground, the surface layers are cooling off and becoming saturated. This cooling is greatly accelerated if the surface is snow- or ice-covered or if the trajectory carries the air over a cold-water surface. Depending on the strength of the air current, fog with light winds or a low stratus deck with moderate to strong winds will form rapidly because of surface cooling. Occasionally fine drizzle will fall from this cloud form, and visibility even with moderate winds will then be very poor. Owing to the rapidity with which the low clouds and fog form within this air mass over very large areas, particularly during the night, flying conditions are hazardous whenever extensive surface cooling is indicated. Frontal lifting of mT air in winter, even after the surface layers have become stabilized, will release the convective instability and yield large amounts of precipitation in the form of rain or snow.

During the winter, air resembling mT is occasionally observed flowing inland over the Gulf and south Atlantic states. Generally this air is cP air that had a relatively short trajectory over the warm water off the southeast coast. Clear weather usually accompanies this type of air in contrast to cloudy weather accompanying a deep current of mT air. On surface synoptic charts, the apparent mT current can be distinguished from true mT currents by the surface dew-point temperature value. True mT air will always have dew-point-temperature values in excess of 60 degrees F. The highly modified cP air will usually have dew-point values between 50 and 60 degrees F.

(c) Maritime Polar (mP): The source region for mP air is either just south of Iceland or east of Newfoundland in the cold Labrador current. Pope AFB usually only sees a modified mP air mass due to the modification that occurs when the air mass travels over land and near the warm Gulf Stream prior to arrival at Pope AFB. The mP air affecting Pope AFB arrives from the northeast generally in the form of a back door cold front (Figure 8). Very low visibilities and ceilings usually last for days with clearing depending on the position of the cold front. mP air usually brings rain with occasional mixed precipitation to the area; snow is rare due to the air mass modification of the Gulf Stream raising the temperatures too high. Thunderstorms aren’t likely with this air mass.

BACKDOOR COLD FRONT H H

H H

Figure 8

Polar maritime air whose origin is in the Atlantic becomes significant at times along the east coast. It is not nearly so frequent over North America as the other types, owing to the normal west-east movement of all air masses. This type of air is observed over the east coast in the lower layers of the atmosphere whenever a cP anticyclone moves slowly off the coast of the Maritime Provinces and New England. This air, originally cP, undergoes less heating than its Pacific counterpart, because the water temperatures are colder and also because it spends less time over the water. This results in the instability being confined to the lower layers of this air. The intermediate layers of this air are very stable owing to the anticyclonic trajectory the air is subjected to. Showers are generally absent; however, light drizzle or snow and attendant low visibility are common. Ceilings are generally on the order of 700 to 1,500 ft with tops of the clouds near 3,000 ft. Marked subsidence above the inversion ensures that convective clouds will not exist above that level.

The synoptic weather condition favorable to mP air over the east coast is usually also ideal for the rapid development of a warm front with maritime tropical air to the south. Maritime tropical air will then overrun the mP air, and a thick cloud deck will form. Clouds extending from near the surface to at least 15,000 ft are then observed. Ceilings will then be near zero, and icing conditions will be severe in the cold air mass. Frequently freezing rain and sleet will be observed on the ground. Towering cumulus clouds prevail in the warm air and often produce thunderstorms.

Flying conditions are rather dangerous with mP air because of turbulence and icing conditions present near the surface. Poor visibility and low ceilings are additional hazards. The cloudiness associated with the mP current usually extends as far west as the Appalachians. The rapidity of the above development is of great concern to all forecasters.

When mT air overruns mP air, flying conditions become impossible over the east coast because of the thickness of clouds.

(d) Continental Arctic (cA): Arctic air comes from the Arctic and it’s COLD. Deep in the winter after a few strong cP outbreaks, Pope AFB may see an outbreak of cA air. These outbreaks are usually associated with an Alberta low and they move very quickly. Due to low moisture content, precipitation (snow) is usually light and of short duration. Winds are very gusty with isolated gusts over 35kts. Temperatures reach around zero at night and go up to near freezing in the day. Clearing is very rapid after frontal passage. Thunderstorms are not likely from this air mass.

(2) Cold Fronts During Winter: Pope AFB experiences arctic and continental polar cold fronts during the winter. Each of these frontal types and associated weather are discussed below.

(a) Arctic Cold Fronts: The Arctic cold front has its source region in the Yukon Territory or the Canadian Basin. It is usually associated with the Alberta low and the Alberta Low Storm Track in mid to late winter. Frontal passage is usually quick, 30- 40kts, with very light precipitation and post-frontal surface winds, northerly 15-20kts with frequent gusts to 30kts and isolated gusts greater than 35kts. Below freezing temperatures, lows 12-18F, highs 28-34 F, for at least two days with gradual warming afterwards. Cloud conditions normally consist of stratocumulus ceilings 3,000-5,000 feet, altostratus or altocumulus 8,000-12,000 feet and cirrus/cirrostratus with polar banding evident in the cirrostratus shield. Visibility remains above 3 miles in the light precipitation. Rapid clearing should be anticipated as the front moves off the east coast.

(b) Continental Polar: The continental Polar cold front-has as its source region the Canadian Basin or the Great Basin. It can be associated with the Alberta, Northern Rocky, Central, Colorado, or Texas Low (see Figure 9) and their respective storm tracks. Frontal passage will be strongest in the winter, can be fairly strong in the autumn and spring, and weak to nonexistent in the summer.

TEXAS LOW H H L L H H H L H L

H H

H L H L H L H H H

H H

Figure 9 Strong polar outbreaks will have much the same characteristics as the cA outbreaks. Moderate polar outbreaks will generally see wave development along the frontal boundary, allowing mT air to mix with the system resulting in lower ceilings, 2,000-3,000 feet, northerly winds 10-15kts with gusts to 20kts, and light precipitation.

In winter, expect post-frontal clear skies and a gradual warming trend after two days unless the high is progged to stagnate over southern Canada and become a prevailing high versus the receding high. The receding high is associated with zonal flow or short wave trofs independent of major long wave systems. This usually foretells the possibility of wave development in the Gulf of Mexico or along the Carolina coast.

The proximity of the warm Gulf current along the Atlantic coast and cold air over the Carolinas combine to breed the dreaded Hatteras Low (Figure 10) or East Coast Storm. Usually, the further south the low develops the more weather Pope AFB will receive.

HATTERAS LOW H H L

H L H H HH H

H H L L

H L H L H H H

Figure 10 The Hatteras Low tends to move more or less northeastward along the Gulf Stream Current, develop to great intensity off the New England coast and stagnate in the general area of Iceland or over the waters between Greenland and Labrador.

Expect deteriorating conditions as the winter low develops. The ceiling will lower from 3,000-4,000 feet to less than 3,000 feet 2-4 hours after initial low development. Continued overrunning plus slight orographic upslope motion will lower ceiling to less than 1,000 feet and light precipitation will begin, or already have begun, lowering the visibility to generally less than 3 miles.

The type of precipitation will be dependent upon the current thickness and type of upper air advection (cold or warm). The amount will be dependent upon available moisture and how rapidly the low moves northeastward.

Expect slow improvement in reported weather as the wraparound from the low pulls further away from Pope AFB. Stations to the west and south will show the first improve- ments and allow the forecaster to develop timing for category changes.

Continental polar outbreaks are also instrumental in the development of the Gulf or East Gulf low (Figure 11). Again, the cold high is of the prevailing type, usually found over the north central United States or south central Canada with surface ridging extending into southern Texas. Warm, moist subtropical air from the Gulf of Mexico enhances the thermal gradient along the Texas Gulf Coast and cyclogensis is possible.

The cyclone will move northeastward, but it could move up either side of the Appalachians. The presence of an inverted trof over the Appalachians usually means the low will move eastward towards the Atlantic, re-curve northeast and follow the storm track of the East Coast Low.

This track will bring the most weather into the Pope AFB area. Extensive overrunning from the Gulf will lower the ceiling from 8,000-12,000 feet to nimbostratus ceilings 4,000-6,000 feet and light precipitation will begin to fall. The ceiling will continue to lower and decrease to less than 3,000 feet 3-5 hours after precipitation begins. The ceiling will lower to less than 1,000 feet 4-7 hours after precipitation starts, except in snow where a rapid decrease in both ceiling and visibility occurs.

If snow is forecast, just drop the ceiling to low cat B (below 500 feet), with intermittent cat A (below 200 feet), and issue the proper advisories. Watch out for freezing precipitation as warm air advects in aloft and the release of latent heat of condensation changes the type of precipitation.

Local area work charts will greatly assist the forecaster in developing timing for the systems. Here, too, stations to the south and west will show initial improvement; caution: watch out for post-frontal fog.

(3) Warm Fronts During Winter: There are two source regions, the Gulf of Mexico and the Atlantic Ocean. It is these two bodies of water that temper and moderate the climate of Pope AFB. Nearly all frontal systems are in some way or another modified by either of these two areas of moisture and heat. With southeasterly flow, advection fog and stratus from the coastal area is possible. Flow from the south or southwest is normally warm and moist; instigating stratus and fog formation as the warmer air is cooled from below and dense fog or stratus develops. Daily inspection of the gradient wind level chart is a good habit to develop when forecasting for Pope AFB. It can preclude the early morning busted forecast of "Severe Clear" to "WOXOF".

Warm frontal passage at Pope AFB is usually associated with the Texas Gulf, or East Gulf Low (Figure 11). The storm track is northeastward west of the Appalachians towards the Ohio Valley.

GULF HLOW H H H H L

H H L H H H L H

Figure 11

Sky conditions at Pope AFB will be quite variable, dependent upon the extent of the overrunning from the Gulf and the speed of the retreating air mass north of Pope AFB.

Multi-layered mid and upper-level broken cloud with scattered varying broken stratocumulus 4,000-6,000 feet is observed prior to warm frontal passage, with visibilities decreasing to about 3 miles just ahead of the front and possible cat A conditions due to fog at the frontal boundary. The ceiling and visibility usually increase rapidly in post-frontal fair skies before overcast stratocumulus 3,000-5,000 feet advect in from the west as the cold front approaches.

(a) Looping Warm Front (Damming). Refer to Figure 7. This front is mostly a winter and transition season phenomena. Synoptically a prevailing high is located over the New England states and a warm blocking high or extension of the sub-tropical ridge is located over the central Georgia area. A quasi-stationary front oriented east-west exists along the Virginia/North Carolina border. Easterly flow, towards the Appalachians, is deflected to the south with damming against the mountains. The frontal boundary will parallel the anticylonically curved isobars from eastern North

Carolina to northern South Carolina to the eastern s1opes of the Appalachians. Continued easterly flow advects in warm moist air which builds downwards along the cold dome and the ceiling will lower to less than 1,000 feet with intermittent light rain or drizzle observed along the frontal boundary. Daytime heating will begin to burn-off the stratus, giving the appearance of northward movement to the frontal boundary. Ceilings will improve to greater than 1,000 feet, but less than 3,000 feet. Continued heating will cause Pope AFB to break around 2000Z, as the warm front disappears. The gradient level wind will veer from easterly to a southerly component, while the surface wind maintains an easterly component prior to the warm front disappearing. This will create low level wind shear that increases with heating, and does not dissipate until the layers mix out. The steeper the lapse rate the stronger the wind shear.

(b) Coastal Warm Front: This mesoscale pseudo-warm or stationary front forms mainly during the winter months in response to the warm Gulf Stream Current and a cold receding high to the north of Pope AFB. The cold high will move slowly from southern Quebec eastward, remaining north of Pope AFB, to a position off the New England coast. The ridge axis on the surface will be oriented northeast-southwest paralleling the Appalachians. The trajectory of the air mass flowing from warm water towards a cold land mass will induce thermal packing along the North Carolina coast. The surface pressure at: HAT, LFI, ECG, and NKT will fall and the surface wind observed at the respective stations will be easterly while the wind at Pope AFB remains northeast. An inverted trof forms along the shore, parallel to the shoreline and acts as a lifting mechanism as the warmer air advect onshore over the cold dome along the eastern Coastal Plain. Dependent upon the strength of the low level circulation and the westward progression of the inverted trof (pseudo warm front), Pope AFB will report ceilings from broken stratocumulus 3,000-5,000 feet to overcast stratus 500 feet. As in the looping warm front, daytime heating will eventually erode the thermal packing and the pseudo-front will wash out.

(4) Occluded Fronts During Winter: Warm and cold air occlusions are rare at Pope AFB, especially warm air occlusions. Only cold air occlusions are addressed below.

Cold air occlusions are limited to the winter months, specifically mid-January to late- February. The synoptic situation most common is: (a) A slow retreating cP air mass over the eastern portion of Canada with surface ridging evident into the Carolinas oriented parallel to the Appalachians. (b) A looping warm front from the Atlantic Seaboard parallels the nose of the cold high to a surface low in western Tennessee. (c) A moderate cP air mass exists over the mid-west. A cold front extends from the surface low in Tennessee southwestward into eastern Texas. (d) The long wave trof is deep with sharp curvature, extending from James Bay southward to the Texas Gulf Coast.

(e) Strong polar or an arctic outbreak is surging south from Canada in conjunction with an 500mb vorticity maximum. Movement is usually in excess of 30kts towards the northwest Gulf.

The surface low in Tennessee will track northeasterly through the Ohio Valley, the cA or cP outbreak will continue moving southeast, picking up speed, re-enforcing the moderate cP air mass. The looping warm front will move slowly northward as the cold high over eastern Canada slowly recedes.

A Gulf low (Figure 11) develops off the Texas Gulf coast in response to the 500mb vorticity maximum and moves east-northeast recurving northeast in Georgia and moves up the frontal boundary in western North Carolina. The triple point will usually develop between Asheville and Hickory, NC, as the stronger cA or cP air moves east faster than the cP, or possible modified mP, can recede.

Pre-frontal weather will include any or all of the following: (a) Freezing precipitation, dependent on the thickness and temperature advection. (b) Mixed precipitation, again dependent on thickness. (c) Low ceilings and poor visibility (d) Low level wind shear; low-level flow is northeast while gradient-level and above winds are normally southerly. (e) Moderate or greater icing; if freezing rain is forecasted, severe. (f) Moderate turbulence below 10,000 feet, cyclonic wind shear.

b. SPRING:

(1) Spring Air Masses And Associated Weather: Spring is the transition between the cold, wet, and foggy winter to the hot, humid, and hazy conditions of summer. In spring, we shift from a predominant air mass of continental polar, with an occasional maritime polar from a back door cold front (Figure 8), to one of maritime tropical as the sub-tropical ridge (Bermuda High) builds over our area. Due to frontal thunderstorms and the now present “air mass” thunderstorms, spring is the most active season. Cold fronts tend to stall over Pope AFB and slowly move south causing low ceilings and visibilities to persist for a day or two after frontal passage from return flow. We may even see a backdoor front with mP characteristics (see mP winter and mP summer) of either summer or winter type as mentioned above.

(a) Continental Polar (cP): After having been the dominant air mass for the winter, this air mass is reluctant to move out as the sub-tropical high builds and forces maritime tropical air into the Pope AFB area. The cP air in place is very modified and has become very unstable. With the addition of moisture from the mT air, thunderstorms in the area become almost a daily occurrence. The colder cP air remains at the surface and tends to lower the wet bulb zero temperature making the chances for severe weather also a good possibility.

(b) Maritime Tropical (mT): This air mass pushes up from the Gulf of Mexico or the Atlantic in response to the building sub-tropical high in the Atlantic. Air mass and weather characteristics are much the same as in the summer.

(c) Maritime Polar (mP): From late winter to early spring, mP air masses will have their strongest influence upon the observed weather at Pope AFB. Heavy snowfall, freezing rain, mixed precipitation, and extended periods of low ceilings and visibilities can accompany the modified mP air mass. The primary region of modification is east of the island of Newfoundland in the weak cold current that flows equatorward from Labrador.

Synoptically, a receding continental cold high moves across the northern United States and becomes a prevailing high off the New England coast with the surface ridge axis oriented northeast-southwest into northern Georgia. The northeast flow pattern, below 850mb, from off-shore pumps in the necessary moisture to saturate the lower layers. A jet maximum at 500mb is located over southern South Carolina and will trigger cyclogensis off the Carolina coast. The surface low will tend to move north-northeast along the Gulf Current up the Atlantic Seaboard.

To forecast the type of precipitation, analyze for the current thickness over Pope AFB and air being advected towards Pope AFB from Wallops Island, VA (72402) and Cape Hatteras, NC (72304). Cold air advection denotes snow, or rain changing to snow, and warm air advection denotes snow becoming freezing rain or snow becoming rain dependent upon surface temperatures. These systems can stagnate off the Carolina coast and new snow accumulation of two to four inches is not uncommon.

(2) Cold Fronts During Spring: The spring transition period at Pope AFB is interspersed with hail, tornadoes, gusty surface winds, and, at times, heavy snow. Historically, the heaviest snowfalls will occur during this period. The 24 hour maximum snowfall for Pope AFB in February is 9.0 inches, and for March 8.0 inches. The forecaster must be alert to rapid modifications occurring throughout the atmosphere. The Gulf, East Gulf, and Hatteras cyclones tend to favor the period of time from late February to mid-March to wreak havoc upon the Atlantic Seaboard.

The strength of cP outbreak will dictate the observed frontal weather at Pope AFB. A moderate outbreak will usually lower the ceiling to 2,000-3,000 feet with multi-layer cloud above. Visibility will remain above three miles in fog and haze, unless precipitation is forecast. If precipitation is forecast, consider lowering the ceiling to less than 1,000 feet and visibility less than 2 miles.

The observed pre-frontal weather associated with weak cP outbreaks is best described as very difficult to forecast. Observations at Pope AFB will reflect conditions varying from below field minimums (WOXOF) to clear skies and unrestricted visibility. Care must be taken in progging these cold fronts through; sometimes they never get here.

During daytime heating, the cold front may stall over the Appalachians, delaying frontal passage. Waves may, and usually do, form along the frontal boundary, again delaying frontal passage.

The worst condition, synoptically, for Pope AFB is a weak cP outbreak that becomes quasi-stationary over Pope AFB with waves. Widespread fog and stratus with intermittent light rain and possible embedded thunderstorms can occur. Worse, the thunderstorm activity could become severe due to the low wet-bulb zero height. Stations to the west, AVL, HKY, CLT, GSP, and GSO, should be closely monitored; surface dew points are usually the best indicators of cold frontal passage. The air mass can change quickly from cP to mT and back again as the front moves north or south of Pope AFB.

(3) Warm Fronts During Spring: The Gulf of Mexico and the Atlantic Ocean continue as the source regions for the mT air masses. Nearly all warm frontal passages through mid-April will be active, unless the surface low tracks northeastward west of the Appalachians. If the surface low tracks east of the Appalachians, the warm front will normally be active.

It is not uncommon for the entire southeast United States to be LIFR or IFR in widespread fog and stratus with precipitation in conjunction with active warm fronts. Typically, the forecaster must search to southern Florida or the northern U.S. to find a suitable alternate for departing aircraft.

(1) Summer Air Masses And Associated Weather: Due to the influence of the sub-tropical high, the dominant air mass of summer is maritime tropical (mT). The only other air masses that interact with Pope AFB during summer are continental polar (cP) and occasionally maritime polar (mP). Summer storms are usually a result of the tug-of- war between cP and mT air masses in an attempt to dominate the Pope AFB weather. When this occurs, Pope AFB can get severe weather and heavy rains.

(a) Continental Polar (cP): cP air is usually well modified when it reaches Pope AFB in the summertime due mainly to heating from below. Frontal passage occurs less frequently in the summer than in the other seasons. After having been well modified, this air mass can have a higher moisture content than it does in other seasons. So, when it collides with another air mass, thunderstorms, squall lines, and severe weather are possible.

(b) Maritime Tropical (mT): As stated earlier, this is the prevailing air mass of the summer. When the Bermuda High sets up in the Atlantic off of the Florida coast, southwest winds pump this air mass into the Pope AFB area from the Gulf of Mexico. High moisture content and high temperatures follow as the sub-tropical ridge keeps the Carolinas relatively cloud free during the day. Lift from afternoon heating is usually enough to spark isolated thunderstorms throughout the area. Thunderstorms average

around nine per month due to afternoon heating, trough passage, and the occasional front.

The weather in the eastern half of the United States is dominated by mT air in summer. As in winter, warmth and excessive amounts of moisture characterize this air. In summer, convective instability extends to higher levels, and there is also a tendency toward increasing instability since the air moves over a warmer land mass. This is contrary to winter conditions.

Along the coastal area of the southern states, the development of stratocumulus clouds during the early morning is typical. These clouds tend to dissipate during the middle of the morning and immediately reform in the shape of scattered cumulus. The continued development of these clouds leads to scattered showers and thunderstorms during the late afternoon. Ceilings in the stratocumulus clouds are generally ample for the operation of aircraft, on the order of 700 to 1,500 ft. Ceilings become unlimited with the development of the cumulus clouds. Flying conditions are generally favorable despite the shower and thunderstorm conditions, since the convective activity is scattered and can be circumnavigated. Visibility is usually good except near sunrise when the air is relatively stable over land.

When mT air moves slowly northward over the continent, ground fogs frequently form at night. Sea fogs develop whenever this air flows over a relatively cold current off the east coast. The fogs over the Grand Banks are usually formed by this process.

(c) Maritime Polar (mP): MP air in the summer is relatively rare, but when it does come it offers cooler temperatures and low ceilings. In spring and summer, this air is occasionally observed over the east coast. Marked drops in temperature that frequently bring relief from heat waves usually accompany the influx of this air. Just as in winter, there is a steep lapse rate in the lower 3,000 ft of this mass. Stratiform cloud forms usually mark the inversion. Ceilings are on the order of 500 to 1,500 ft and the tops are usually 500 to 1,000 ft higher. No precipitation occurs from these cloud types. Owing to turbulence in the surface layers, visibility is usually good. This air usually does not constitute a severe hazard to flying.

(2) Cold Fronts During Summer: The Canadian Basin is the source region for cP air masses for the summer months. Diurnal heating modifies the cold air mass significantly prior to arrival at Pope AFB. The cold fronts are usually inactive becoming active over the water east of Pope AFB. The cold fronts do enhance thunderstorm activity and squall line formation is possible along with severe weather.

As in the latter part of spring, the cold front will: (a) Stall-out prior to passage at Pope AFB-forecast will usually reflect morning patchy fog and stratus with isolated afternoon showers and airmass thunder-storms. (b) Become quasi-stationary in the general vicinity of Pope AFB-forecaster should consider greater probability of dense morning fog and low stratus

ceilings along with increased chance of few afternoon showers and thunderstorms. (c) Pass through, become quasi-stationary over southern Gulf states, and return northward as a very weak warm front. Watch out for fog and stratus over the southeast if the front returns northward. (d) Pass through and wash-out over the northern Gulf-one or two days of fair weather, decreased chance of afternoon thunderstorms, then back to air mass thunderstorms and shower activity.

(3) Warm Fronts During Summer: Warm frontogenesis usually occurs when modified cP or mP air mass stalls out south of Pope AFB. Warm frontal passage may be active or inactive, dependent upon the period of time of re-modification. If the front is forecast to return poleward in 36-48 hours, expect patchy fog and stratus, with some areas, primarily along the Appalachians, with ceilings less than 1,000 feet. Slightly increased instability may produce some very isolated shower activity and the temperature usually increases 5 to 8 degrees Fahrenheit with warm frontal passage.

The active warm frontogenesis normally occurs when the cold front passes through Pope AFB, becomes quasi-stationary over the southern gulf states, and the re- modification process takes 3 to 5 days, dependent upon the strength of the cooler air mass. A good indicator that the warm front is beginning to move poleward is the widespread fog and stratus being reported in the southern gulf states.

In conjunction with the cooler air mass retreating and the southerly low-level advection of warm moist air over the cooler land mass, the fog and status will advect towards the Pope AFB area. If no cloud is being reported above the stratus layer, expect break-up by 1200L; later if cloud is present above the layer.

(d) AUTUMN

(1) Autumn Air Masses And Associated Weather: Autumn and spring are very alike in air mass characteristics. Maritime tropical air, after having been dominant for the summer, is now slowly being replaced by continental polar air. Frontal passages are usually weak and result in few thunderstorms. After frontal passage, high pressure builds in and moves off coast usually resulting in fog/stratus for the 2 to 3 days following frontal passage.

(2) Autumn Cold Fronts: The cold fronts are initially weak to moderate becoming stronger with time during the transition from summer to winter. Historically, autumn is the driest season of the year.

In September, the frequency of cold frontal passage is usually decreased due to the warm blocking high, an extension of the Bermuda High, that develops over the southern U.S. The southern portion of the cold front may undergo frontolysis in the mid-west, as the upper air support moves northeasterly over the top of the blocking high. Persistent

haze, due to subsidence, with visibility five miles or less is observed until the first good surge of polar air arrives at Pope AFB.

The vast majority of cold fronts will usually be inactive as the mean upper flow is northerly, dry. Backdoor frontal passages (Figure 8) are more common during the autumn months versus the more customary north-south oriented cold front. The cP high migrates from the Canadian Basin across the northern US to southeast Quebec then moves south and east towards the New England coast. The cold front will move south with an easterly component through the Carolinas into northern Georgia and will undergo frontolysis, or become a looping warm front (Figure 7). Sky conditions during cold frontal passages may vary from stratocumulus ceilings 3,000-4,000 feet to fair skies. The cold dome is usually below 850mb.

If the cP air mass stagnates off the New England coast, easterly flow beneath the subsidence inversion can result in very persistent dense fog and low stratus ceilings with layered stratocumulus to 5,000 feet. Light rain and drizzle will be observed if the flow pattern remains stagnant and the cP will modify to mP.

The ceiling will slowly lift to above 1,000 feet by 1400L, but lower to less than 1,000 feet after 2000L. The visibility will increase to 3 miles or greater, also by 1400L, and trend downwards after 2000L. Expect the same conditions to persist until the cooler air retreats far enough north to allow heating to break the inversion or there is a new front progged through.

Thunderstorm activity does not usually accompany the frontal passages due to drier air aloft, upper level subsidence and more stable air.

As the Bermuda High weakens and migrates equatorward, the more customary north/south oriented cold fronts will begin to migrate through the Pope AFB area and stronger cP outbreaks should be expected to occur, These cold fronts may be active or inactive depending upon the upper level flow.

If the flow is such that it allows moisture from the Gulf of Mexico to mix with the system, it will be active. If flow from the Gulf is shut-off from the system, it will probably be inactive. Inactive cold fronts will be accompanied by freezing temperatures, very light precipitation (if any) gusty surface winds, and stratocumulus ceilings 4,000-6,000 feet. Active cold fronts will be accompanied by ceilings generally beneath 3,000 feet, possible mixed precipitation, lowered visibilities, post-frontal gusty surface winds and freezing temperatures.

e. TROPICAL STORMS AND HURRICANES: On the average only two hurricanes hit the SE US each year. The principal hurricane months are August through October, with a peak in September.

(1) Early season storms (June through early July) originate in the western Caribbean and move into the Gulf of Mexico striking the Mexican coast of the Gulf coast states.

(2) During July through October they develop in the eastern Atlantic near the Cape Verde Islands. Nearly all of them move westerly, some reaching the US coast before recurving north and east.

(3) In late September through November they once again develop in the western Caribbean. But, unlike the earlier storms turn north and northeastward in the lower latitudes brushing Florida or the Greater Antilles.

(4) The average life span of a hurricane is 9 days. August hurricanes average 12 days, July and November hurricanes last about 8 days.

f. CLIMATIC AIDS: Data for this section is taken from the International Station Meteorological Climate Summary (ISMCS), 1983-1993.

(1). Liquid Precipitation: Monthly liquid precipitation data for Pope AFB is presented in Table 2.

Table 2. Monthly Climatic Liquid Precipitation Data for Pope AFB, NC

MONTH MEAN 24 HR MAX MEAN # OF MONTHLY AMOUNT (in) DAYS WITH MAX (in) PRECIP (in) JAN 3.60 2.81 10 8.07 FEB 3.84 4.83 9 7.86 MAR 4.14 3.15 10 7.81 APR 3.30 4.80 8 9.22 MAY 3.50 3.05 10 7.97 JUN 4.57 4.25 10 11.70 JUL 6.15 5.62 12 15.76 AUG 4.90 4.34 11 13.11 SEP 3.90 4.52 8 16.41 OCT 3.34 5.08 7 10.40 NOV 2.93 5.16 7 9.40 DEC 3.17 2.57 9 7.84

(2). Frozen Precipitation: While one may think snow does not occur in the South, snow has been recorded at Pope AFB as early as November and as late as April. Refer to the data in Table 3 below from the ISMCS.

Table 3. Monthly Climatic Frozen Precipitation Data for Pope AFB, NC

MONTH MEAN 24 HR MAX MEAN # OF MONTHLY AMOUNT (in) DAYS WITH MAX (in) PRECIP (in) JAN 1.10 9.10 1 16.0 FEB 1.00 9.10 1 11.1 MAR 0.70 8.00 1 11.2 APR 0.00 0.80 0 0.80 NOV 0.00 0.10 0 0.10 DEC 0.70 14.0 1 16.9

Section 4: Synoptic/Mesoscale Weather Regimes:

1. General Forecast Rules for CONUS Regime Types

(a). ALBERTA CLIPPER/NORTHERN ROCKIES LOW. Typically these storms travel north of the area, but with Northwesterly flow aloft, these systems can have some impact. These type systems travel too fast to obtain Gulf Moisture or have much effect on the surface airmass. However, on occasion, short lived but intense snowfall can occur. This snowfall is usually very dry (20:1 ratio) but because of the rapid movement of the system, snowfall totals average less than an inch.

(b). GULF LOW. Gulf Lows will move either east or west of the Appalachians. The presence of an inverted trough over the Appalachians usually means the low will move eastward towards the Atlantic and then re-curve northeast. This track brings the most weather to Pope. Extensive overrunning from the Gulf will lower the ceilings from 8,000- 12,000 Ft to 4,000-6,000 Ft with light liquid precipitation. 3-5 hours after precipitation begins, anticipate ceilings to steadily drop to around 3,000 Ft and between 4-7 hours to 1,000 Ft. A quicker transition to lower ceilings is usually associated with snowfall in this situation. As with any winter storm system, be alert for frozen and freezing precipitation and post-frontal Fog. When the storm system travels along the western side of the Appalachians there is the higher potential to enter the warm sector of the system. Net effect on ceilings and weather is the same, although precipitation type will transition more easily.

(c). TEXAS LOW. This surface low forms in Texas and the upper trough has enough amplitude that the low will track up the western side of the Appalachians. Due to a mix of terrain effects and, if available, cold air forced against the Appalachians (Cold air damming) – the warm front will appear to “wrap around” the mountains and foothills. Be reluctant to move the warm front out as quickly as the low is moving up the western side of the mountains. Wedges of cold air normally remain in place until the cold trough breaks down or moves eastward and the surface flow turns eastward to southeastward creating low-level warm advection. These scenarios can bring widespread low ceilings/visibilities and precipitation. The temperature profile of any in-place wedge of cold air east of the Appalachians must be closely monitored to forecast mixed/solid precipitation events. These wrap around fronts can be very persistent and Models tend to forecast them to break down 12 to 24 hours earlier than when breakdown actually occurs. In a more Zonal Flow, stable waves originating in the Texas panhandle area typically move across the southern states, generally exiting the South Carolina coast. Frequently, the northern branch of the 500 mb maximum wind band is across the Great Lakes region and has a slight northwesterly tilt. Confluence of the northern and southern branches create a sharp east to west northern edge to the cloud pattern associated with the wave. When the confluent area is north of the forecast area, the station can experience 6 to 12 hours of light precipitation and stratocumulus ceilings. During the winter, these type systems can draw enough warm air above the cold wedge to give us frozen or freezing precipitation.

(d). HATTERAS LOWS. These systems develop in the Gulf of Mexico, move northeastward across Georgia (sometimes up the southeastern seaboard) and deepen over Hatteras, hence the name Hatteras Low. Well developed Hatteras Lows are more commonly called Nor’easters. A Hatteras Low forming in the Gulf and crossing over Georgia usually gives Pope area a dense cirrus shield and the cloud cover lowers progressively (similar to that of a warm front). In general, the ceilings are middle cloud when the low is in the gulf and may become stratocumulus (<5,000 feet) as the low moves north of the Savannah area. Ceilings may continue to lower progressively to less than 1,000 feet as the low center passes between Pope and the coast. Precipitation may begin as light intensity as the low leaves the Gulf and become moderate as the low enters southeastern South Carolina. Systems that cross Florida and move up the coast generally do not produce prolonged periods of less than 1,000 feet ceilings unless they stall and deepen rapidly in the Hatteras area. A system in the Hatteras area can wrap low-level moisture around the backside and produce IFR conditions until the low moves north of the Virginia capes. A classic winter Nor’easter may pull enough cold air down the backside to produce a rain/snow mix before it moves out of the region. After the wrap around cloud moves out with the Hatteras Low, expect 1 to 2 days of gusty winds and scattered cold air stratocumulus.

(e). COLORADO LOW. The Colorado Low track and its variants typically move the surface low through the Great Lakes region into the Canadian Maritime Provinces. The more zonal Colorado Low track can occasionally produce severe convection as the upright cold front moves east of the Appalachians. These systems frequently open the Gulf and bring warm and moist air into the southeast.

(f). CALIFORNIA LOW. The California Low is associated with a cut-off upper low over southern California or off the coast of southern California. A ridge is in place over the southeastern states. The maximum wind band can have a southwesterly tilt from Pope to New England or across the Canadian Rockies anticyclonically, meandering southwesterly to the Great Lakes region and turning mildly cyclonically through New England. In any case, the trajectories of lows and waves vary so greatly that one cannot describe a stereotypical scenario. The weather in the southeast is generally fair with temperatures above normal. Patchy morning fog can occur when low-level trajectories are from the ocean, transitioning to afternoon cumulus. The polar front remains well north of the forecast area and little occurs in the way of significant weather.

(g). BERMUDA HIGH SOUTH. In general, summer weather across the forecast area is controlled by the Bermuda High and the associated ridge axis. When the Bermuda High ridge axis is south of Pope, the region will be dominated by air that has been adiabatically warmed and dried by the Appalachians. Maximum temperatures are higher than normal and heat stress conditions begin early in the day. When the ridge is south of the forecast area, occasional weak cold fronts or short wave troughs can produce isolated outbreaks of severe thunderstorms. Thunderstorms are generally late afternoon with surface heating being the principle trigger. They are usually slow moving, produce locally heavy rainfalls, and frequently of the pulse type. Visibilities less

than three miles at sunrise are rare except in areas that had late afternoon or early evening heavy rainfall the day before. Ceilings are infrequent except in the vicinity of thunderstorms or post thunderstorm convective debris areas. Ceilings in convective debris areas are usually broken middle cloud and are dissipated by late evening.

(h). BERMUDA HIGH NORTH. When the Bermuda High ridge migrates to a position north of the forecast area, the station comes under more of a true maritime tropical forecast regime. The predominant surface flow becomes southeasterly and downslope and adiabatic warming are no longer a factor in the local forecast. Temperatures are moderated to an afternoon maximum of 86 to 88 F and low-level relative humidity increases dramatically, consequently the moisture available for convection increases. Air mass LCL, CCL, and Tc lower significantly and convection begins earlier in the day, frequently by late morning. Very moist maritime air may turn over by late morning, regain some instability due to afternoon heating, and produce a second bout of convection by mid to late afternoon. Depth of the tropical easterly flow must be monitored, and when it becomes sufficiently deep (approximately surface to 500mb), the upstream oceanic areas must be monitored for tropical waves. Tropical waves can be detected by using satellite loops and successfully extrapolated into the forecast area. Tropical cyclone development must be closely monitored and National Hurricane Center products made a part of the forecast process. In the ridge north air mass, ceilings are more frequent and wide spread. Occasionally this air mass can have patchy sunrise stratus and visibilities of 2 to 3 miles in fog. Middle cloud heights are generally lower and convective debris is more widespread and persistent, frequently lasting until sunrise before breaking up. Thunderstorms that develop in deep southeasterly flow rarely produce surface gusts of 35 knots or greater and are mostly heavy rainfall and lightning producers. Severe thunderstorm activity in deep southeasterly flow is extremely rare and will normally only be found in tropical cyclone rain bands.

(i). BACK DOOR COLD FRONT. When the ridge line is depressed southward by intrusions of summer polar air, weak back door cold fronts can reach the area. In the best case, a back door frontal passage may bring lower relative humidity and welcome relief from heat. If the boundary stalls across central or southern North Carolina, it may act as a differential heating surface and provide a good thunderstorm trigger for 1 to 2 days. These fronts generally move back northward as the ridge in the polar westerlies moves off New England and flow begins to return to easterly and then southeasterly.

2. Severe Weather Forecast Techniques

(a). THUNDERSTORMS. While thunderstorms occur at Pope during all months, all most half of Pope’s 46 annual thunderstorm days (27) occur during the summer months of June through August. Percent frequency of occurrence from hourly observation discloses the "obvious fact" that the principle thunderstorms trigger is afternoon heating during the summer months. Outside the summer months, thunderstorm occurrences are more randomly scattered throughout the day and are mainly the result of pure dynamics with troughs or fronts being the principle trigger. Air mass thunderstorms (those not produced by moving fronts, troughs or line squalls) are usually not severe. These

storms generally produce light to moderate rainshowers, wind gusts less than 34 knots, and cloud-to-ground lightning. On rare occasions, conditions can exist during which an air mass thunderstorm may become pulse severe and forecasters must metwatch for the precursor signature of elevated high reflectivities building downward. Springtime is considered to be the most likely season for severe thunderstorms that are produced by squall lines or strong cold fronts. These fast moving storms generally come from the southwest to northwest quadrant and can produce heavy rainfalls, surface gusts exceeding 50 knots, considerable lightning, and upon rare occasions, hail or tornadic activity. Ample evidence indicates that most spring thunderstorms, even associated with fronts and squall lines, are less than severe and much more likely to produce moderate rainfalls and winds in the 30-40 knot range.

(b). TORNADOES. Tornadoes rarely occur in the Ft Bragg/Pope area and are usually F0 or F1 intensity on the Fujita Scale. These small North Carolina tornadoes are suspected to be more related to boundary layer vortices than resulting from classic downwardly stretching mesocyclones and conservation of angular momentum. Most occurrences will be associated with strong squall lines or boundary collisions. The remaining occurrences will generally be associated with the rain bands of tropical cyclones (convergent asymptotes). Tropical cyclone tornadoes will have deceptively low tops and reflectivities, but very high low-level helicity. Again, probable boundary layer generation.

(c). HAIL. Pope averages less than 1 recorded hail observation per year and this is most likely to occur during the spring to early summer period mainly due to optimum wet bulb zero heights.

(d). HURRICANES/TROPICAL STORMS. While the "official” hurricane season is June 1 – November 30, the maximum numbers of storms are grouped into August and September. Tropical cyclones may affect the region in many ways, but neither Pope Air Force Base nor Simmons AAF has ever officially recorded sustained hurricane force winds due to a tropical cyclone. The area did, however, experience gusts to 110 mph at Fayetteville's Grannis Airport during Hazel in 1954.

The difficulty in correctly forecasting tropical cyclone winds is resolved somewhat by the fact that National Hurricane Center Bulletins must be interpreted literally. While track forecasts are subject to large errors over time, the storm bulletins alleviate the inconsistencies that would occur among regional forecasters. While the forecasting of hurricane force winds for base officials is of paramount importance, forecasting amounts of rainfall, local flooding potential, and effects of tropical cyclone weather elements such as tornadic potential in the rain bands may be equally as important. Saturated soils from torrential rains frequently combine with tropical storm intensity winds to create extended power outages.

Hurricanes and tropical storms making landfall on the Gulf Coast frequently drift northeast and may deposit as much as 6 to 10 inches of rain on the region in less than 36 hours. Occasionally a decaying system may retain enough tropical intensity to cause

severe weather as the outer rain bands cross the forecast area. Potentially, an exiting system can reintensify as it moves over the Atlantic waters.

3. Fog and Stratus Forecast Techniques

(a). FOG. Fog at Pope AFB is relatively easy to forecast. About 95% of the time we will have 100% humidity during the early morning hours and because of that you would assume that we would have fog in the morning. The truth is that the wind direction is more important to forecasting fog than the humidity. Ex. If you have Northeast winds coming anticyclonically around a High located in West Virginia and 100% humidity, you will not get the fog in the morning (less than 3 miles). That is because your flow is a dry flow coming from the Midwest. On the other hand, if you have Northeast winds coming cyclonically around a Low off the South Carolina coast and 100% humidity, you will get fog in the morning (less than 3 miles). That’s because your flow is a moist flow coming from the Atlantic Ocean.

Another factor that must be considered in fog forecasting is residual moisture. If your flow is coming from a land source but you know that there were heavy rainshowers in that direction the night before, you will more than likely forecast fog the next morning (less than 3 miles). You must consider how much precipitation fell and how much that precipitation evaporated before the sun set or the inversion set up. How far the visibility will decrease due to fog is another forecasting concern. I did a study of the relationship of the temperature to the minimum visibility and came up with these results. If your minimum temperature is between 13 and 17 degrees Celsius and fog is forecasted, the chances of going down to “A” Category increase significantly. I think the reason for this is because when your temperature is colder than 13 degrees, the atmosphere can’t hold enough moisture for the visibility to drop significantly. Conversely, if your temperature is above 17 degrees, the atmosphere is to warm and evaporation is happening just enough to keep the visibility from dropping significantly. One other thing to consider is that if there is precipitation happening at the time then these rules no longer apply.

(b). STRATUS. Stratus clouds are a product of a stable atmosphere and relative humidities of 65% or greater. Areas of stratus will favor straight or slightly cyclonically curved contours. Anticyclonically curved contours will favor fog. A retreating fall anticyclone moving offshore and warm moist advection from the southeast, combined with slight upslope motion, and nocturnal cooling can lead to a widespread stratus cloud shield. Stratus formation will favor late night hours toward sunrise. Monitoring of coastal observations and use of low cloud enhancement EA1 on IR satellite pictures are helpful in determining onset. The Wind Stratified Conditional Climatology (CC tables) is an excellent tool for determining duration.

Late Fall, Winter, and early Spring Hudson Bay/Backdoor Front episodes can lead to persistent fog and stratus occurrences. Key to a northeast fog/stratus episode is orientation and amplitude of the surface/gradient level ridge. If the ridge is oriented northeast-southwest and the over-water trajectory of the cool polar air is long enough, it will quickly acquire low-level moisture. The more the flow is straight line, the greater the

likelihood of elevated stratus. With a slow moving polar high, the northeast flow scenario can affect visual flight operations for as many as 3 days with ceilings and visibilities becoming progressively lower each day. With knowledge of the depth of the moist layer and the CC tables, these stratus scenarios can be successfully forecasted. Often the key to breaking down a northeast low stratus episode is the forecasting of the surface winds to a warmer, more easterly direction. With warm easterly low-level advection, a cold dam will break down quickly.

A third stratus pattern favors the straight line prefrontal pretrough flow. These patterns generally have higher surface/gradient wind speeds and produce higher stratus. Often this stratus will appear as a scattered layer after first light and will have mixed and dissipated by mid morning. This stratus often heralds the moisture for afternoon thunderstorms or rainshowers.

When a slow moving cold front (California low/Colorado low) is approaching with an open gulf, low-level gulf moisture can advect into the forecast area. This forecast scenario is advection stratus and as such can occur any hour of the day. It will, however, respond to diurnal heating by having lowest ceilings around sunrise and the highest ceilings during the afternoon. Gulf stratus is usually the leading moisture in a precipitation producing pattern and should not be viewed as a radiation phenomena. When precipitation begins out of middle cloud or high stratocumulus ceilings, a stratus layer will often form below 1,000 feet. This stratus can occur through the evaporation of moisture into the sub-cloud layer through precipitation process. It generally occurs as surface relative humidity reaches 65-70% and winds mix and saturate the air producing a cloud layer. As precipitation continues, the scattered layer will increase to broken or overcast. In a continuous light rain situation, scattered stratus will appear in 1 to 3 hours and become broken by 4 to 6 hours, most often appearing at 600 to 900 feet.

4. WINDS

Surface winds ≥ 25 knots are most likely frontal associated and favor afternoon hours with directions southwesterly prefrontal or northwesterly post frontal. An occasional strong winter or spring cold front can cause ≥ 25 knots independent of diurnal heating, but highest winds will usually be during daylight hours. Surface winds greater than 35 knots are usually convective gusts, but can occur once or twice per winter with very strong cold fronts.

Surface winds outside of a frontal environment are strongly affected by diurnal heating and cooling and should be expected to be at maximum speed near maximum temperature and minimum speed near minimum temperature. Wind profiles including data from Skew-T, wind profilers, meteograpms, and WSR-88D VAD wind profile are all useful in determining when and at what temperature the inversion will break. This will coincide with the time in which the winds aloft begin to reach the surface. Average wind speed is 70% of the maximum observed low-level wind and peak gusts may equal the highest wind speed during maximum heating. In moderate to strong cold air advection, peak speeds can exceed the highest value observed in the low-level wind field.

Forecasting Wind Direction is relatively easy. The direction will be from approximately 30 degrees to the left of the Isobars toward the High Pressure. They come out of the High and into the Low. A good rule of thumb for the wind speed forecast. This has to do with gradient winds. If you have four millibars of pressure gradient within 125 miles of Pope AFB then forecast at least 20 knots of wind. What you do is go out 125 miles perpendicular to the isobars from Pope AFB and if you have four millibars of change then expect greater than 20 knots of wind.

5. ALTIMETER

Forecasting the Altimeter is pretty straight forward at Pope AFB. The only point that needs to be made is that you must consider the diurnal effects on the pressure. If you have Low/High Pressure over you and it is not expected to change then go with the diurnal variation to forecast the altimeter. If you have a Low/High pressure moving in you must still consider the diurnal change. Ex. If you have a Low Pressure moving in, your pressure will probably hold steady during the diurnal increase and drop significantly with the diurnal decrease. See figure 11 below for example diurnal curves for Jan & Jul:

Figure 11

Section 5: Forecast Techniques/Rules of Thumb:

RULES OF THUMB

There are currently no approved rules of thumb (ROTs) for Pope AFB. Supplied below is a list of approved and tested ROTs from Simmons AAF. The validity of the ROTs is determined by the % correct which is the % of cases where the ROT actually occurred.

1 Oct - 30 Apr a. If R1 on the 12hr forecast line of the NGM is >= 90%, consider forecasting ceilings < 1,000’ for that time period (54% correct). b. If R1 on the 12hr forecast line of the NGM is >= 90%, consider forecasting ceilings < 3,000’ for that time period (73% correct). c. If R1 on the 12hr forecast line of the NGM is >= 80%, consider forecasting ceilings < 3,000’ for that time period (66% correct). d. If R1 on the 12hr forecast line of the NGM is >= 90%, consider forecasting cig/vis < 1,000/3 for that time period (53% correct). e. If R2 on the 12hr forecast line of the NGM is >= 70%and VV is positive, consider forecasting precipitation for that time period (69% correct). f. If R1+R2 on the 12hr forecast line of the NGM is >= 125 and VV is positive, consider forecasting precip for that time period (56% correct). g. If R1 on the 24hr forecast line of the NGM is >= 90%, consider forecasting ceilings < 3,000’ for that time period (67% correct). h. If R1 on the 24hr forecast line of the NGM is >= 80%, consider forecasting ceilings < 3,000’ for that time period (59% correct). i. If R2 on the 24hr forecast line of the NGM is >= 70% and VV is positive, consider forecasting precipitation for that time If R1 on the 36hr forecast line of the NGM is >= 90%, consider forecasting ceilings < 3,000’ for that time period (73% correct). j. If R2 on the 12hr forecast line of the NGM is >= 70% and VV is positive, consider forecasting precipitation for that time period (73% correct).

1 May - 30 Sept a. If R1 on the 24hr forecast line of the NGM is >= 90%, consider forecasting ceilings < 3,000’ for that time period (66% correct). b. If R2 on the 12hr forecast line of the NGM is >= 70% and VV is positive, consider forecasting precipitation for that time period (61% correct).

Section 6: Forecast Studies and Research:

Approved Local Forecast Studies

No studies at this time.

Section 7: Contingency/Exercise Areas:

See mobility binder.

Section 8: Miscellaneous Information:

Ranges and Routes supported by Pope Weather Flight

Updated by Lt Carter on 02 Mar 07.