DOCSLIB.ORG

A Local Large Hail Probability Equation for Columbia, Sc

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Local Large Hail Probability Equation for Columbia, Sc EASTERN REGION TECHNICAL ATTACHMENT NO. 98-6 AUGUST, 1998 A LOCAL LARGE HAIL PROBABILITY EQUATION FOR COLUMBIA, SC Mark DeLisi NOAA/National Weather Service Forecast Office West Columbia, SC Editor’s Note: The author’s current affiliation is NWSFO Mt. Holly, NJ. 1. INTRODUCTION Skew-T/Hodograph Analysis and Research Program, or SHARP (Hart and Korotky Billet et al. (1997) derived a successful 1991). The dependent variable, hail diameter probability of large hail (diameter greater than or the absence of hail, was derived from or equal to 0.75 inch) equation as an aid in spotter reports for the CAE warning area from National Weather Service (NWS) severe May, 1995 through September, 1996. There thunderstorm warning operations. Hail of that were 136 cases used to develop the regression diameter or larger requires a severe equation. thunderstorm warning be issued by NWS offices. Shortly thereafter, a Weather The LPLH was verified using 69 spotter Surveillance Radar-1988 Doppler (WSR- reports from the period September, 1996 88D) radar probability of severe hail (POSH) through September, 1997. The POSH was became available for warning operations (Witt verified as well. Verification statistics et al. 1998). This study recreates the steps included the Brier score and the chi-square taken in Billet et al. (1997) to derive a local (32) statistic. probability of large hail equation (LPLH) for the Columbia, SC National Weather Service The goal of this study was to develop an Forecast Office (CAE) warning area, and it objective method to estimate the probability assesses the utility of the LPLH relative to the of large hail for use in forecast operations. POSH. Since the WSR-88D algorithms also produce a POSH, the locally produced method was A logistic regression approach was used to verified in comparison to determine if the develop a LPLH for the CAE warning area. local regression equation was more accurate. Independent variables included in the LPLH Since Billet et al. (1997) used data from a were vertically integrated liquid (VIL) and the WSR-88D and an upper air sounding that ratio of VIL to echo top height (ET), both were co-located while this study did not, computed by the WSR-88D; and 500-hPa similarities and differences in the results from temperature at Peachtree City, Georgia (FFC) Billet et al. (1997) are discussed. and Charleston, South Carolina (CHS) extracted from upper air soundings using the 1 2. DATA index, total totals index, bulk Richardson number, equilibrium level, echo top height The dependent variable in the study was the (ET), speed shear in the layer between 200 h- categorical (binary) representation of the Pa and 500 h-Pa, and vertically integrated occurrence of large hail. Dependent variable liquid (VIL) density. VIL density, which is data were obtained from reports from local the ratio of VIL to ET, has been shown to be fire, police, and postal workers, trained useful in discriminating between severe and spotters, NWS employees, and others. non-severe storms (Paxton and Shepherd Independent variable data were obtained from 1993). the WSR-88D and upper air soundings from Peachtree City, Georgia (FFC) and WSR-88D independent variable values came Charleston, South Carolina (CHS) archived from storm interrogation within 20 minutes of locally and extracted via SHARP. the time of hail, or in the cases when hail was reported not to have occurred, from storm Potential independent variables include the interrogation during the same period at the following: time of maximum VIL. This information came from local Archive III and Archive IV 1) vertically integrated liquid optical disks. Most of the time, upper air 2) vertically integrated liquid density variable values came from the most recent 3) lifted index FFC soundings. The soundings were 4) convective available potential energy modified at the surface to match CAE 5) sweat index temperature and dew point at the time of hail 6) total totals index occurrence. 7) bulk Richardson number 8) 700-500-hPa lapse rate The FFC sounding is launched approximately 9) 850-hPa temperature 210 miles from CAE, but it was determined to 10) 700-hPa temperature be the most representative sounding of the 11) 500-hPa temperature CAE warning area in most cases. All other 12) 300-hPa temperature soundings except the WSO Greensboro 13) precipitable water (GSO) and CHS soundings are launched 14) 700-hPa dewpoint depression farther away from CAE than the FFC 15) freezing level sounding. The GSO sounding is launched 16) wet-bulb zero level too far north to be as representative as the 17) equilibrium level FFC sounding. The fairly frequent marine 18) echo top height influence on the CHS sounding usually 19) storm-relative helicity rendered it less representative than the FFC 20) storm-relative directional shear sounding. However, in four of the 136 cases, 21) positive shear there was an air-mass boundary between CAE 22) mean storm relative inflow (sfc to 2 km) and FFC that made the most recent FFC 23) 500-200-hPa speed shear sounding less representative of the atmosphere over CAE than the CHS The list of potential independent variables sounding. In those cases, the CHS sounding was similar to Billet et al. (1997). Variables was used. The CHS sounding is launched not utilized by Billet et al. (1997) were: sweat approximately 95 miles from CAE. 2 In order to maximize the number of cases for that is common to locations with sparse the logistic regression technique, virtually all populations was that the occurrence of hail hail reports and all verifiable reports of no may be unreported and/or undetected. The hail were counted as cases. There were only CAE warning area has many parts that are two limiting criteria. The first was that only sparsely populated. This study went to one report per thunderstorm cell was retained. considerable lengths to minimize these For a given cell, when there were more than sources of error. one report of hail, one hail report was chosen at random. 3. EQUATION When there were one report of hail and one or more reports of no hail, the hail report was A commercially available statistical software chosen. When there were no reports of hail package was used to derive a probability of and more than one report of no hail, one no- large hail equation using logistic regression hail report was chosen at random. The second analysis. The logistic regression approach limiting criterion was that all cases were results in an equation that expresses the between 14 and 105 miles from the radar site. probability of some categorical event (in this The minimum distance was necessary to avoid case, the occurrence of large hail) as the sum problems with the radar’s “cone of silence.” of weighted values of quantifiable variables. The maximum distance was the shortest A complete explanation of logistic regression distance that encompassed the entire CAE can be found in Freeman (1987). warning area. There were 136 cases used to derive the equation. Of those 136 cases, 44 The statistic used to select independent were of no hail, 37 were of small hail variables in this approach is the likelihood (diameter less than 0.75 inch), and 55 were of ratio chi-square statistic (G2). G2 relates large hail. directly to the discrepancies between (a) the predicted number of categorical event Two potential sources of error in the occurrences and non-occurrences from a independent data (sounding based) were that model and (b) the actual number of event the radar site and the sounding sites were not occurrences and non-occurrences. A model collocated, and that soundings were not with a high G2 value has little or no predictive coincident in time with storms. Another value; so, the more model G2 is reduced by possible source of error in the independent inclusion of a given independent variable, the data (radar based) was that in most cases only better the predictive value of that variable. A a data interval was available for VIL. A VIL p-value is associated with the reduction in G2 of 40 up to but not including 45 kg m-2 was by a given variable, and in this case the p- designated as 40 kg m-2, a VIL of 45 up to but value is the chance of obtaining such a not including 50 kg m-2 was designated as 45 reduction randomly. Therefore, low p-values kg m-2, and so on. are associated with variables that have high predictive value. A source of error in the dependent data was the estimation of hail sizes by spotters. Very The first step of this regression approach is to few spotters actually measure hail diameter. run each potential independent variable in a Another source of error in the dependent data one-independent variable equation, and the 3 variable that results in the greatest reduction correlated, the results themselves are not in G2 is kept (provided the associated p-value contaminated. Among the three independent is less than or equal to .05). The next step is variables retained in this study, only VIL and to run each remaining variable together with VIL density were significantly correlated. the one kept from the previous step in a two- Pearson’s product-moment correlation independent variable equation. The one that coefficient between the two values was .7578. results in the greatest reduction in G2 is also The p-value of the correlation was zero with kept. This process is continued until the 134 degrees of freedom. In this case, the p- reduction in G2 resulting from keeping the value meant that the probability of obtaining “best” remaining independent variable has an such a high correlation coefficient between associated p-value greater than .05.
Load more

Recommended publications
  • Use Style: Paper Title
    Environmental Conditions Producing Thunderstorms with Anomalous Vertical Polarity of Charge Structure Donald R. MacGorman Alexander J. Eddy NOAA/Nat’l Severe Storms Laboratory & Cooperative Cooperative Institute for Mesoscale Meteorological Institute for Mesoscale Meteorological Studies Studies Affiliation/ Univ. of Oklahoma and NOAA/OAR Norman, Oklahoma, USA Norman, Oklahoma, USA [email protected] Earle Williams Cameron R. Homeyer Massachusetts Insitute of Technology School of Meteorology, Univ. of Oklhaoma Cambridge, Massachusetts, USA Norman, Oklahoma, USA Abstract—+CG flashes typically comprise an unusually large Tessendorf et al. 2007, Weiss et al. 2008, Fleenor et al. 2009, fraction of CG activity in thunderstorms with anomalous vertical Emersic et al. 2011; DiGangi et al. 2016). Furthermore, charge structure. We analyzed more than a decade of NLDN previous studies have suggested that CG activity tends to be data on a 15 km x 15 km x 15 min grid spanning the contiguous delayed tens of minutes longer in these anomalous storms than United States, to identify storm cells in which +CG flashes in most storms elsewhere (MacGorman et al. 2011). constituted a large fraction of CG activity, as a proxy for thunderstorms with anomalous vertical charge structure, and For this study, we analyzed more than a decade of CG data storm cells with very low percentages of +CG lightning, as a from the National Lightning Detection Network throughout the proxy for thunderstorms with normal-polarity distributions. In contiguous United States to identify storm cells in which +CG each of seven regions, we used North American Regional flashes constituted a large fraction of CG activity, as a proxy Reanalysis data to compare the environments of anomalous for storms with anomalous vertical charge structure.
    [Show full text]
  • Chapter 8 Atmospheric Statics and Stability
    Chapter 8 Atmospheric Statics and Stability 1. The Hydrostatic Equation • HydroSTATIC – dw/dt = 0! • Represents the balance between the upward directed pressure gradient force and downward directed gravity. ρ = const within this slab dp A=1 dz Force balance p-dp ρ p g d z upward pressure gradient force = downward force by gravity • p=F/A. A=1 m2, so upward force on bottom of slab is p, downward force on top is p-dp, so net upward force is dp. • Weight due to gravity is F=mg=ρgdz • Force balance: dp/dz = -ρg 2. Geopotential • Like potential energy. It is the work done on a parcel of air (per unit mass, to raise that parcel from the ground to a height z. • dφ ≡ gdz, so • Geopotential height – used as vertical coordinate often in synoptic meteorology. ≡ φ( 2 • Z z)/go (where go is 9.81 m/s ). • Note: Since gravity decreases with height (only slightly in troposphere), geopotential height Z will be a little less than actual height z. 3. The Hypsometric Equation and Thickness • Combining the equation for geopotential height with the ρ hydrostatic equation and the equation of state p = Rd Tv, • Integrating and assuming a mean virtual temp (so it can be a constant and pulled outside the integral), we get the hypsometric equation: • For a given mean virtual temperature, this equation allows for calculation of the thickness of the layer between 2 given pressure levels. • For two given pressure levels, the thickness is lower when the virtual temperature is lower, (ie., denser air). • Since thickness is readily calculated from radiosonde measurements, it provides an excellent forecasting tool.
    [Show full text]
  • DEPARTMENT of GEOSCIENCES Name______San Francisco State University May 7, 2013 Spring 2009
    DEPARTMENT OF GEOSCIENCES Name_____________ San Francisco State University May 7, 2013 Spring 2009 Monteverdi Metr 201 Quiz #4 100 pts. A. Definitions. (3 points each for a total of 15 points in this section). (a) Convective Condensation Level --The elevation at which a lofted surface parcel heated to its Convective Temperature will be saturated and above which will be warmer than the surrounding air at the same elevation. (b) Convective Temperature --The surface temperature that must be met or exceeded in order to convert an absolutely stable sounding to an absolutely unstable sounding (because of elimination, usually, of the elevated inversion characteristic of the Loaded Gun Sounding). (c) Lifted Index -- the difference in temperature (in C or K) between the surrounding air and the parcel ascent curve at 500 mb. (d) wave cyclone -- a cyclone in which a frontal system is centered in a wave-like configuration, normally with a cold front on the west and a warm front on the east. (e) conditionally unstable sounding (conceptual definition) –a sounding for which the parcel ascent curve shows an LFC not at the ground, implying that the sounding is unstable only on the condition that a surface parcel is force lofted to the LFC. B. Units. (2 pts each for a total of 8 pts) Provide the units used conventionally for the following: θ ____ Ko * o o Td ______C ___or F ___________ PGA -2 ( )z ______m s _______________** w ____ m s-1_____________*** *θ = Theta = Potential Temperature **PGA = Pressure Gradient Acceleration *** At Equilibrium Level of Severe Thunderstorms € 1 C. Sounding (3 pts each for a total of 27 points in this section).
    [Show full text]
  • Severe Weather Forecasting Tip Sheet: WFO Louisville
    Severe Weather Forecasting Tip Sheet: WFO Louisville Vertical Wind Shear & SRH Tornadic Supercells 0-6 km bulk shear > 40 kts – supercells Unstable warm sector air mass, with well-defined warm and cold fronts (i.e., strong extratropical cyclone) 0-6 km bulk shear 20-35 kts – organized multicells Strong mid and upper-level jet observed to dive southward into upper-level shortwave trough, then 0-6 km bulk shear < 10-20 kts – disorganized multicells rapidly exit the trough and cross into the warm sector air mass. 0-8 km bulk shear > 52 kts – long-lived supercells Pronounced upper-level divergence occurs on the nose and exit region of the jet. 0-3 km bulk shear > 30-40 kts – bowing thunderstorms A low-level jet forms in response to upper-level jet, which increases northward flux of moisture. SRH Intense northwest-southwest upper-level flow/strong southerly low-level flow creates a wind profile which 0-3 km SRH > 150 m2 s-2 = updraft rotation becomes more likely 2 -2 is very conducive for supercell development. Storms often exhibit rapid development along cold front, 0-3 km SRH > 300-400 m s = rotating updrafts and supercell development likely dryline, or pre-frontal convergence axis, and then move east into warm sector. BOTH 2 -2 Most intense tornadic supercells often occur in close proximity to where upper-level jet intersects low- 0-6 km shear < 35 kts with 0-3 km SRH > 150 m s – brief rotation but not persistent level jet, although tornadic supercells can occur north and south of upper jet as well.
    [Show full text]
  • An 18-Year Climatology of Derechos in Germany
    Nat. Hazards Earth Syst. Sci., 20, 1–17, 2020 https://doi.org/10.5194/nhess-20-1-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. An 18-year climatology of derechos in Germany Christoph P. Gatzen1, Andreas H. Fink2, David M. Schultz3,4, and Joaquim G. Pinto2 1Institut für Meteorologie, Freie Universität Berlin, Berlin, Germany 2Institute of Meteorology and Climate Research, Department Troposphere Research, Karlsruhe Institute of Technology, Karlsruhe, Germany 3Centre for Crisis Studies and Mitigation, University of Manchester, Manchester, UK 4Centre for Atmospheric Science, Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK Correspondence: Christoph P. Gatzen ([email protected]) Received: 18 July 2019 – Discussion started: 4 September 2019 Revised: 7 March 2020 – Accepted: 17 March 2020 – Published: Abstract. Derechos are high-impact convective wind events 1 Introduction that can cause fatalities and widespread losses. In this study, 40 derechos affecting Germany between 1997 and 2014 are analyzed to estimate the derecho risk. Similar to the Convective wind events can produce high losses and fatal- United States, Germany is affected by two derecho types. ities in Germany. One example is the Pentecost storm in The first, called warm-season-type derechos, form in strong 2014 (Mathias et al., 2017), with six fatalities in the region southwesterly 500 hPa flow downstream of western Euro- of Düsseldorf in western Germany and a particularly high pean troughs and account for 22 of the 40 derechos. They impact on the railway network. Trains were stopped due to have a peak occurrence in June and July.
    [Show full text]
  • Stability Analysis, Page 1 Synoptic Meteorology I
    Synoptic Meteorology I: Stability Analysis For Further Reading Most information contained within these lecture notes is drawn from Chapters 4 and 5 of “The Use of the Skew T, Log P Diagram in Analysis and Forecasting” by the Air Force Weather Agency, a PDF copy of which is available from the course website. Chapter 5 of Weather Analysis by D. Djurić provides further details about how stability may be assessed utilizing skew-T/ln-p diagrams. Why Do We Care About Stability? Simply put, we care about stability because it exerts a strong control on vertical motion – namely, ascent – and thus cloud and precipitation formation on the synoptic-scale or otherwise. We care about stability because rarely is the atmosphere ever absolutely stable or absolutely unstable, and thus we need to understand under what conditions the atmosphere is stable or unstable. We care about stability because the purpose of instability is to restore stability; atmospheric processes such as latent heat release act to consume the energy provided in the presence of instability. Before we can assess stability, however, we must first introduce a few additional concepts that we will later find beneficial, particularly when evaluating stability using skew-T diagrams. Stability-Related Concepts Convection Condensation Level The convection condensation level, or CCL, is the height or isobaric level to which an air parcel, if sufficiently heated from below, will rise adiabatically until it becomes saturated. The attribute “if sufficiently heated from below” gives rise to the convection portion of the CCL. Sufficiently strong heating of the Earth’s surface results in dry convection, which generates localized thermals that act to vertically transport energy.
    [Show full text]
  • Weather in the Vertical Ed Williams FPI Feb/March 2008
    Copyright © Ed Williams 2008 Weather in the Vertical Ed Williams FPI Feb/March 2008 http://edwilliams.org/ What’s it all about? • Why is the vertical temperature and moisture profile so important? – Atmospheric stability – Characteristics of stable/unstable wx. • How can we use vertical soundings (“Skew-T”) plots to augment our wx briefings? – Cloud layers and tops – Thunderstorm potential – Icing potential – Fog, mountain waves… A little weather “theory” is good for you! • To understand what is happening, it helps to know why. • The more we know, the less likely we are to be taken by surprise. • We most likely don’t have the skill and knowledge of a professional meteorologist. But we do have the advantage of being on the spot, in real time. Parcel theory is a tool to assess vertical motion in the atmosphere Vertical motion leads to: Clouds Precipitation Thunderstorms Icing Turbulence Warm front The air’s response to lifting is determined by its stability: We assess this by hypothetically lifting parcels (imaginary bubbles) of air. Actual lifting can come from a variety of causes: Fronts Cold Front Orographic etc. Stable systems return towards equilibrium when displaced Stable Unstable Conditionally Unstable • A region of the atmosphere is stable if on lifting a parcel of air, its immediate tendency is to sink back when released. • This requires the displaced air to be colder (and thus denser) than its surroundings. Balloons (and air parcels) rise if they weigh less than the air they displace. Pressure is the weight per unit area of the air above. “Warm air rises” – but it’s a little more complicated.
    [Show full text]
  • PHAK Chapter 12 Weather Theory
    Chapter 12 Weather Theory Introduction Weather is an important factor that influences aircraft performance and flying safety. It is the state of the atmosphere at a given time and place with respect to variables, such as temperature (heat or cold), moisture (wetness or dryness), wind velocity (calm or storm), visibility (clearness or cloudiness), and barometric pressure (high or low). The term “weather” can also apply to adverse or destructive atmospheric conditions, such as high winds. This chapter explains basic weather theory and offers pilots background knowledge of weather principles. It is designed to help them gain a good understanding of how weather affects daily flying activities. Understanding the theories behind weather helps a pilot make sound weather decisions based on the reports and forecasts obtained from a Flight Service Station (FSS) weather specialist and other aviation weather services. Be it a local flight or a long cross-country flight, decisions based on weather can dramatically affect the safety of the flight. 12-1 Atmosphere The atmosphere is a blanket of air made up of a mixture of 1% gases that surrounds the Earth and reaches almost 350 miles from the surface of the Earth. This mixture is in constant motion. If the atmosphere were visible, it might look like 2211%% an ocean with swirls and eddies, rising and falling air, and Oxygen waves that travel for great distances. Life on Earth is supported by the atmosphere, solar energy, 77 and the planet’s magnetic fields. The atmosphere absorbs 88%% energy from the sun, recycles water and other chemicals, and Nitrogen works with the electrical and magnetic forces to provide a moderate climate.
    [Show full text]
  • Atmospheric Stability
    General Meteorology Laboratory #7 Name ___________________________ Date _______________ Partners _________________________ Section _____________ Atmospheric Stability Purpose: Use vertical soundings to determine the stability of the atmosphere. Equipment: Station Thermometer Min./Max. Thermometer Anemometer Barometer Psychrometer Rain Gauge Psychometric Tables Barometric Correction Tables I. Surface observation. Begin the first 1/2 hour of lab performing a surface observation. Make sure you include pressure (station, sea level, and altimeter setting), temperature, dew point temperature, wind (direction, speed, and characteristics), precipitation, and sky conditions (cloud cover, cloud height, & visibility). From your observation generate a METAR and a station model. A. Generate a METAR for today's observation B. Generate a station model for today's observation. II. Plot the sounding On the skew T-ln p plot the CHS sounding. Locate the lifting condensation level (LCL), the level of free convection (LFC), and the equilibrium level (EL). 1. The LCL is found by following the dry adiabat from the surface temperature and the saturation mixing ratio from the dew point temperature. Where there two paths intersect, we would have condensation taking place. This is the LCL and represents the base of the cloud. 2. The LFC is found by following a moist adiabat from the LCL until it intersects the temperature sounding. Beyond this level a surface parcel will become warmer than the environment and will freely rise. 3. The EL is found by following a moist adiabat from the LFC until it intersects the temperature sounding again. At this point the surface parcel will be cooler than the environment and will no longer rise on its own accord.
    [Show full text]
  • A Physically Based Parameter for Lightning Prediction and Its Calibration in Ensemble Forecasts
    4.3 A Physically Based Parameter for Lightning Prediction and its Calibration in Ensemble Forecasts David R. Bright* NOAA/NWS/NCEP/Storm Prediction Center, Norman, Oklahoma Matthew S. Wandishin CIMMS/University of Oklahoma, Norman, Oklahoma Ryan E. Jewell and Steven J. Weiss NOAA/NWS/NCEP/Storm Prediction Center, Norman, Oklahoma 1. INTRODUCTION that explicitly predict moist convection do not predict the occurrence of lightning. Thus, after The Storm Prediction Center (SPC) issues determining where moist convection is plausible, forecasts for the contiguous United States related the potential for thunderstorms must be deduced to hazardous convective weather including through further interrogation of the data. In thunderstorms, severe thunderstorms, tornadoes, addition to deterministic NWP output, the and elements critical to fire weather such as dry NCEP/EMC Short Range Ensemble Forecast lightning. In addition to severe weather products (SREF) is available to the SPC and attempts to such as watches and outlooks, the SPC also account for initial condition, model, and convective issues “general” thunderstorm outlooks for the physics uncertainty (Du et al. 2004). The SPC contiguous United States and adjacent coastal post-processes the NCEP SREF to create a suite waters. These outlooks delineate a > 10% chance of customized ensemble products specifically for of cloud-to-ground (CG) lightning within thunderstorm and severe thunderstorm prediction approximately 15 miles of a point. (For the (Bright et al. 2004). A subset of these products is purposes of this paper, a thunderstorm is defined available in real-time on the SPC web site at as deep convection producing at least one CG http://www.spc.noaa.gov/exper/sref/.
    [Show full text]
  • Prmet Ch14 Thunderstorm Fundamentals
    Copyright © 2015 by Roland Stull. Practical Meteorology: An Algebra-based Survey of Atmospheric Science. 14 THUNDERSTORM FUNDAMENTALS Contents Thunderstorm Characteristics 481 Thunderstorm characteristics, formation, and Appearance 482 forecasting are covered in this chapter. The next Clouds Associated with Thunderstorms 482 chapter covers thunderstorm hazards including Cells & Evolution 484 hail, gust fronts, lightning, and tornadoes. Thunderstorm Types & Organization 486 Basic Storms 486 Mesoscale Convective Systems 488 Supercell Thunderstorms 492 INFO • Derecho 494 Thunderstorm Formation 496 ThundersTorm CharacterisTiCs Favorable Conditions 496 Key Altitudes 496 Thunderstorms are convective clouds INFO • Cap vs. Capping Inversion 497 with large vertical extent, often with tops near the High Humidity in the ABL 499 tropopause and bases near the top of the boundary INFO • Median, Quartiles, Percentiles 502 layer. Their official name is cumulonimbus (see Instability, CAPE & Updrafts 503 the Clouds Chapter), for which the abbreviation is Convective Available Potential Energy 503 Cb. On weather maps the symbol represents Updraft Velocity 508 thunderstorms, with a dot •, asterisk *, or triangle Wind Shear in the Environment 509 ∆ drawn just above the top of the symbol to indicate Hodograph Basics 510 rain, snow, or hail, respectively. For severe thunder- Using Hodographs 514 storms, the symbol is . Shear Across a Single Layer 514 Mean Wind Shear Vector 514 Total Shear Magnitude 515 Mean Environmental Wind (Normal Storm Mo- tion) 516 Supercell Storm Motion 518 Bulk Richardson Number 521 Triggering vs. Convective Inhibition 522 Convective Inhibition (CIN) 523 Triggers 525 Thunderstorm Forecasting 527 Outlooks, Watches & Warnings 528 INFO • A Tornado Watch (WW) 529 Stability Indices for Thunderstorms 530 Review 533 Homework Exercises 533 Broaden Knowledge & Comprehension 533 © Gene Rhoden / weatherpix.com Apply 534 Figure 14.1 Evaluate & Analyze 537 Air-mass thunderstorm.
    [Show full text]
  • Sounding Analysis
    Operational Weather Analysis … www.wxonline.info Chapter 11 Sounding Analysis Introduction The term “sounding” is used in meteorology to describe a vertical plot of temperature, dew point temperature, and wind above a specific location. It provides a picture of how these parameters change as you rise into the atmosphere. These vertical data are used to determine atmospheric stability, precipitation type, and a glimpse of cloud location at one point in time. The primary source for these data is the radiosonde, an instrument package that is launched at numerous locations around the world at 00 UTC and 12 UTC. This coordinated launch provides a three-dimensional picture of the structure of the atmosphere twice a day. The actual launch time is one hour prior to nominal observation time due to the time it takes for the instrument to rise into the stratosphere. On a good day, the radiosonde will reach the 10 mb level. Another source of sounding data is satellite sounders. Due to their asynoptic nature, these data are usually integrated via data assimulation into computer forecast models. These soundings tend to be smoother than radiosonde profiles. Soundings are also available from computer forecast models. At most forecaster workstations you can click on a point on a map and get a forecast sounding for that location. This allows you to evaluate future soundings for precipitation type or stability. Radiosonde Data : A radiosonde is an instrument package that measures temperature, relative humidity and atmospheric pressure (RAOB). These data are transmitted back to the launch site by radio. Temperature, relative humidity and pressure can be used to calculate dew point temperature and the height of a pressure level, and a variety of other variables.
    [Show full text]