GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

AIR MASSES

Air Mass: large body of air with similar properties of ______and ______in any ______.

Source Region:

Ideal Source Regions a) b)

Major source regions are found in the: a) ______and b) ______

1. TEMPERATURE a) b) c) d)

2. MOISTURE a) b)

There are five types of air masses associated with North America

1. Maritime Tropical (_____) 4. Continental Polar (_____) 2. Continental Tropical (______) 5. Continental Arctic (______) 3. Maritime Polar (_____)

3. STABILITY INDICATORS a) Stable (w) - air mass is ______than the ______'w' air masses:

b) Unstable (k) - air mass is ______than the ______.e.g., mPk 'k' air masses:

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AIR MASS MODIFICATION

Air masses move out of their source regions • Properties are ______by the ______• Modification occurs because of: o Exchange of ______with the surface o ______o ______associated with large-scale vertical motions e.g., cP air mass modifies as it moves SE into the southern U.S. e.g., cP air mass crosses the east coast and moves over the western Atlantic. Evaporation from the sea leads to large areas of low clouds/fog. Example of heating and destabilization. e.g., cP traveling over snow-covered ground is NOT modified as much (due to albedo of surface)

Five Air Masses affecting North America

1. cA (Continental Arctic) - ______a. Source: Rarely reaches U.S., but when it does, ______

2. cP (Continental Polar) - ______a. Source: Moves into ______resulting in ______down to Gulf of Mexico

3. mP (Maritime Polar) - ______a. ______for this air mass ______and ______b. ______air masses affect U.S. more than the ______c. Pacific: originally ______air - moved over ______

4. cT (Continental Tropical) - ______a. Source: ______. ______important air mass to the United States - ______and… b. Only influences the U.S. in the ______

5. mT (Maritime Tropical) - ______a. ______for this air mass ______and ______b. Gulf of Mexico/Subtropical Atlantic Ocean Winter: 1. lower layer of air is ______:

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2. meet ______air;

Summer: 1. 2.

c. Pacific 1. 2. More ______3. Contributes to ______in California 4. Brings ______precipitation in winter

WEATHER IMPACTS FROM AIR MASSES

LAKE-EFFECT SNOW

* ______moves across the Great Lakes

* Air ______through ______from the warm water.

* The warm air starts to ______producing ______.

* Once the air reaches the ______, the clouds deposit large quantities of ____

SIBERIAN EXPRESS

* A large ______, ______air mass moves from ______* A ______dominates the region (central U.S.)

* Combination of ______and ______cause ______temperatures.

NOR’EASTER

* Usually occur during ______

* Slow moving ______moves to the north of ______with a ______moving up the ______.

* Causes ______wind of ______air to the south (______)

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* Colder air from north may come in contact with warm air from the south causing ______

* Situation can cause strong ______winds, heavy ______, coastal ______, ______

FRONTS

Front: A sloping boundary between air masses with different properties of:

A front is also associated with a ______in the pressure pattern.

The slope of the front influences the ______that form.

Types of Fronts and Symbols

The type of front is determined by ______: e.g., cold front =

Stationary Front

a.

b. surface winds blow ______, but in ______on either side of the front

c. slopes from surface toward ______

d. weather:

e. precipitation:

f. location: colder air usually on the ______

Page 4 of 4 GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

Cold Front

Usually occurs where

Slope is ______than that with a warm front (or stationary front)

If warm air is ______, thunderstorms may form and a ______can develop.

If warm air is ______, nimbostratus and altostratus may form.

Typical Weather Conditions Associated with a Cold Front Weather Element Before Passing While Passing After Passing Winds south-southwest gusty, shifting west-northwest Temperature warm sudden drop steadily dropping Dew Point high; remains steady sharp drop lowering Clouds incr. Ci, Cs, then either Tcu or Cb often Cu Tcu* or Cb Pressure falling steadily minimum, then sharp rising steadily rise Precipitation short period of heavy showers of rain or decreasing showers snow, sometimes with intensity of hail, thunder, and showers, then lightning clearing Visibility fair to poor in haze poor, followed by good except in improving showers * Tcu stands for towering cumulus, such as cumulus congestus; whereas Cb stands for cumulonimbus.

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Warm Front

Usually occurs where

Characteristics similar to a ______front.

Initial cirrus may be more than ______

Typical Weather Conditions Associated with a Warm Front Weather Element Before Passing While Passing After Passing Winds South-southeast-east variable south-southwest Temperature Cool-cold, slow steady rise warmer, then warming steady Dew Point Steady rise steady rise, then steady Clouds In this order: Ci, Cs, stratus-type clearing with As, Ns, St, and fog; scattered Sc; occasionally Cb in occasionally Cb in summer summer Pressure usually falling leveling off slight rise, followed by fall Precipitation light-to-moderate rain, drizzle or none usually none, snow, sleet, or drizzle sometimes light rain or showers Visibility poor poor, but improving fair in haze

Page 6 of 6 GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

Cold Front vs. Warm Front Precipitation

Cold Front:

Precipitation location:

Intensity:

Duration:

Warm Front:

Precipitation location:

Intensity:

Duration:

Occluded Front

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Occurs when a ______and ______a warm front. Typically form ______in a cyclone’s life cycle.

3 types of occlusions: determined by ______between the air behind the cold front and ahead of the warm front. • ______(most common east of Rockies) o air behind cold front is ______than air ahead of warm front o weather is like a ______during frontal passage

• ______( most common in the Pacific NW) o air behind the cold front is ______as air ahead of warm front o weather is like a ______during frontal passage

• ______o ______between air masses, marked by ______

Typical Weather Conditions Associated with a Cold-Type Occluded Front Weather Element Before Passing While Passing After Passing Winds southeast-south variable west to northwest Temperature Cold Type cold-cool dropping colder Warm Type cold rising milder Dew Point steady usually slight drop, slight drop, although especially if cold- may rise a bit if occluded warm-occluded Clouds in this order: Ci, Cs, Ns, sometimes Tcu or Ns, As, or scattered As, Ns Cb Cu Pressure usually falling low point usually rising Precipitation light, moderate, or light, moderate, or light-to-moderate heavy precipitation heavy continuous precipitation precipitation or followed by general showers clearing Visibility poor in precip. poor in precipitation improving

Criteria used to locate a front on a surface weather map

Page 8 of 8 GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

1. ______over a relatively short distance

2. changes in the air’s ______content (change in ______)

3. shifts in the wind ______

4. ______and ______

5. ______and ______patterns

EXTRA-TROPICAL (MID-LATITUDE) CYCLONES

The extra-tropical cyclone (mid-latitude cyclone, low pressure, or low), is a major weather maker in the mid and high latitudes. Surface winds blow ______Surface winds ______

Life Cycle of Extra-Tropical Cyclones (Norwegian Cyclone Model)

Cyclogenesis (birth of a cyclone)

• starts along the ______as a ______• sets up ______(______) • location is directly under an area of ______• ______develops with ______as shown in the figure • ______as cyclonic circulation develops • westerlies aloft ______as it grows

Wave Cyclone

• central pressure continues to ______and winds strengthen due to increased ______• upper level trough ______and is located ______center • warm sector is better defined • fronts form a pronounced ______and ______in satellite images • extensive ______cloudiness is ______• cyclone moves ______at 25-35 mph

Beginning of Occlusion

Page 9 of 9 GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

• warm sector ______and occluded front ______• upper level pattern shows ______and is ______• ______the cold front cloud band from the comma cloud • cyclone moves ______at ~ 20 mph

Bend-Back Occlusion

• surface low may become ______from the westerly steering flow and the occluded front is ______of the low • warm sector is ______from the cyclone center • ______favors development of a secondary cyclone • eventually the cyclone weakens (______)

Entire cycle can occur over ______if upper level conditions are ideal. ______will result in poorly defined systems.

Extra-Tropical (mid-latitude) Cyclone Weather

Figure 10. 12 in your text represents an intensifying cyclone in the Upper Midwest.

Extra-Tropical Cyclones: cold side or warm side Storm track determines weather at points on the ground • Track A puts Chicago on the ______with passage of fronts • Track B puts Chicago on the ______with no frontal passages • Study this idea…you’ll do this in lab and on a test.

UPPER AIR FLOW

* Developing surface storm systems are ______that usually ______. * What happens when an upper-level low is located ______the surface low? It ______

* Air flow aloft in the mid-latitudes usually consists of a series of ______(______)

Convergence: Divergence:

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This type of convergence is also called ______This type of divergence is also called ______

Convergence and divergence also result from ______

Convergence Aloft: Divergence Aloft:

For a surface low to develop or intensify, upper level ______of air must be ______than surface ______.

PUTTING IT ALL TOGETHER . . .

* Winds aloft ______of surface storms.

* Surface lows should move to the ______.

* Surface highs should move to the ______.

* Surface systems move at ~ ______of the ______winds.

* If a surface low is under upper level ______, it will ______.

* If a surface high is under upper level ______, it will ______.

Page 11 of 11 GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

Principal Extra-tropical cyclone tracks • Tracks tend to converge toward the ______(head to the______) • Tracks appear to originate ______, but actually form over the ______. Just ______over the mountains, but then ______. • Cyclones that form in the ______(access mT)

500 mb map of Northern Hemisphere shows 5 longwaves (______or ______) encircling the globe.

Longwaves can remain ______, move east very slowly (______) or move west (______)

Imbedded in longwaves are ______: small ______or ______

The ______the wavelength, the ______it moves downstream.

Shortwaves move east at a speed close to the ______

Shortwaves tend to ______when they approach a ______(1 and 3), and ______when they approach a ______(2).

Contour lines ______to isotherms = ______and windflow is ______

Contour lines ______isotherms = ______and temperature ______occurs. Near ______. Distinct air mass regions exist. Always baroclinic near mid-latitude cyclones.

Page 12 of 12 GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

Advection Examples: 1. no advection

2. Stronger ______, greater ______

3. closer______implies ______ transport temperature ______efficiently

The greater the angle (up to 90 degrees) between winds and isotherms, the ______will take place. The isobars and isotherms form parallelograms or boxes (sometimes called solenoids); the size of the boxes is ______to the intensity of advection.

In the diagram above: more ______advection taking place than ______advection.

Smaller boxes imply ______. Larger boxes imply ______.

So… ______= wind must blow across the isotherms from colder to warmer regions. See blue arrows in diagram on previous page. ______= wind must blow across the isotherms from warmer to colder regions. See red arrows in diagram on previous page.

(a) Longwave 500 mb trough over stationary front. Currently ______

Page 13 of 13 GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

(b) Shortwave ______and creates ______in the flow = baroclinic instability

This causes horizontal and vertical motions that ______.

Convergence at 1 (creates “___”) and divergence at 2 (creates “____”)

Cold air advection is occurring at position _____, cold air brought into the ______.

Cold air is dense and ______of the 500 mb surface. ______= lower ______. So trough ______. Cold, heavy air also sinks here.

At position _____, warm air advection ______and builds the ridge. Warm air rises here and condensation releases latent heat to fuel storm.

(c) Storm ______and storm should start to weaken now.

Warm moist air is ______from storm with cold dry air drawn into the center of surface low.

Upper low has been ______. Upper and surface low are now ______.

Winds slacken, pressure ______and low is said to be ______.

Jet Streaks… Strongest winds in the core of the jet = ______or ______Tend to form in ______where pressure gradients are ______

If curved jet streak, then div at point 3 and con at point 1

______(“D”) of jet streak will draw ______upwards which will enhance the cyclone causing further pressure drops This storm has proper ______

Vorticity, Divergence, and Developing Storm Systems

Anything spinning has ______Faster spinning = ______

When viewed from above…

Page 14 of 14 GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

• air that spins ______has ______• air that spins ______has ______

Two types: ______and ______

Northern Hemisphere: earth’s vorticity (______) is always ______Because earth spins ______.

Vorticity depends on ______: ______

Moving air will usually have additional vorticity relative to the earth’s surface = ______vorticity

Two causes of ______: 1. 2.

Absolute vorticity =

* Earth’s vorticity at any latitude =

When upper-level divergence moves over a weak cyclonic circulation, ______(more positive) and ______

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