atm ocn 100 - summer 2002 lectures 32 & 33

ATM OCN 100 Summer 2002ATM OCN 100 Summer 2002 11

ATM OCN 100 - Summer 2002ATM OCN 100 - Summer 2002LECTURES 32 & 33LECTURES 32 & 33

THUNDERSTORMS:THUNDERSTORMS: MESOSCALE CONVECTIVE SYSTEMSMESOSCALE CONVECTIVE SYSTEMS

A. INTRODUCTIONA. INTRODUCTION– Practical QuestionsPractical Questions

What is a thunderstorm?What is a thunderstorm? Why do thunderstorms occur?Why do thunderstorms occur?

– Definitions Definitions (where...)(where...)

MADISON’S CURRENT WEATHERMADISON’S CURRENT WEATHER

Madison Weather at 1000 AM CDT WED AUG 8 2001 Updated twice an hour at :05 and :25

Sky/Weather: SUNNY Temperature: 83 F (28 C) Dew Point: 71 F (21 C) Relative Humidity: 67% Wind: W7 MPH Barometer: 30.04F


Surface Weather Map from Today Surface Weather Map from Today with with IsobarsIsobars & Fronts & Fronts


Current Temperatures (Current Temperatures (ooF) & IsothermsF) & Isotherms


Current Dewpoints Current Dewpoints ((ooF) F)


Current Winds Aloft at 34,000 Ft.Current Winds Aloft at 34,000 Ft.


Tomorrow’s 7AM ForecastTomorrow’s 7AM Forecast


A. INTRODUCTION A. INTRODUCTION (con’t.)(con’t.)

DefinitionsDefinitions– AA thunderstorm thunderstorm - contains thunder;- contains thunder;

– A A thunderstorm day thunderstorm day -- a day with thunder. a day with thunder.

A Mesoscale PhenomenonA Mesoscale Phenomenon


CumulonimbusCumulonimbus


Thunderstorm Hazards-Thunderstorm Hazards-

Lightning Lightning

Lightning is a killer (with more than 80 deaths in US per year)!


Historical Thunderstorm Charge Historical Thunderstorm Charge ModelModel


New Conceptual Model of Charge New Conceptual Model of Charge Structure in Deep Convection from Structure in Deep Convection from

Balloon DataBalloon Data


Thunderstorm Hazards-Thunderstorm Hazards-Flash FloodsFlash Floods

Flash Flooding is a killerFlash Flooding is a killer (with more than 120 deaths in US(with more than 120 deaths in US per year)! per year)!


Thunderstorm Hazards-Thunderstorm Hazards-TornadoesTornadoes

Tornadoes are killers (with more than 60 deaths in US per year)!


Funnel CloudFunnel Cloud

When funnel clouds touch the ground they become…….


TornadoesTornadoes


Thunderstorm Hazards-Thunderstorm Hazards-High Winds (Straight line)High Winds (Straight line)


Thunderstorm Hazards-Thunderstorm Hazards-Large HailLarge Hail


B. THUNDERSTORM GENESISB. THUNDERSTORM GENESIS

Essential IngredientsEssential Ingredients

– Low Level MoistureLow Level Moisture

– Unstable Atmospheric Lapse RateUnstable Atmospheric Lapse Rate

– Trigger (Trigger (or or Kicker)Kicker) Initial Setting & Initiation ProcessesInitial Setting & Initiation Processes

– Free ConvectionFree Convection

– Forced ConvectionForced Convection


When Convection?When Convection?


STABLE CONDITIONSSTABLE CONDITIONSCompare Compare EnvironmentEnvironment with with DALRDALR

Colder parcel sinks & returns to startColder parcel sinks & returns to start

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ABSOLUTELY STABLE CONDITIONSABSOLUTELY STABLE CONDITIONSCompare Compare EnvironmentEnvironment with with SALRSALR & & DALRDALR


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UNSTABLE CONDITIONSUNSTABLE CONDITIONS

Compare Compare EnvironmentEnvironment with with DALRDALR Warmer parcel continues upward Warmer parcel continues upward

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ABSOLUTELY UNSTABLE CONDITIONSABSOLUTELY UNSTABLE CONDITIONS

Compare Compare EnvironmentEnvironment with with SALRSALR & & DALRDALR Warmer parcel continues upwardWarmer parcel continues upward

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If STABLE CONDITIONS for DryIf STABLE CONDITIONS for DryCompare Compare EnvironmentEnvironment with with DALRDALR


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But UNSTABLE CONDITIONS for HumidBut UNSTABLE CONDITIONS for HumidCompare Compare EnvironmentEnvironment with with SALRSALR Warmer parcel continues upwardWarmer parcel continues upward

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CONDITIONALLY STABLE CONDITIONSCONDITIONALLY STABLE CONDITIONSCompare Compare EnvironmentEnvironment with with SALRSALR & & DALRDALR

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Stability CriteriaStability CriteriaSee Fig. 6.14 Moran & Morgan (1997)See Fig. 6.14 Moran & Morgan (1997)


STABILITY CRITERIASTABILITY CRITERIA Absolutely StableAbsolutely Stable

– Layer lapse rate less than saturation Layer lapse rate less than saturation adiabatic lapse rate.adiabatic lapse rate.

Absolutely UnstableAbsolutely Unstable– Layer lapse rate greater than dry adiabatic Layer lapse rate greater than dry adiabatic

lapse rate.lapse rate. Conditionally UnstableConditionally Unstable

– Layer lapse rate lies between dry & Layer lapse rate lies between dry & saturation adiabatic lapse rates.saturation adiabatic lapse rates.


STATIC STABILITY STATIC STABILITY (con’t.)(con’t.)

• Processes which change static stability Processes which change static stability (instability)(instability)

• Cool below, but warm above Cool below, but warm above (stabilize)(stabilize)• Warm below, but cool above Warm below, but cool above (destabilize)(destabilize)

• Visual stability indicatorsVisual stability indicators


MammatusMammatus

These pocket clouds form from sinking air ahead of the most severe thunderstorms. If you see these….run for cover!!!!


Hail StonesHail Stones


Hail StormHail Storm


THE “TRIGGER”THE “TRIGGER” Free ConvectionFree Convection

– Air ascends due to destabilization;Air ascends due to destabilization;– Heat surface and/or cool aloft.Heat surface and/or cool aloft.

Orographic LiftingOrographic Lifting– Air ascends mountain slopes.Air ascends mountain slopes.

Frontal LiftingFrontal Lifting– Air ascends along cold front.Air ascends along cold front.

Dynamic LiftingDynamic Lifting– Upper level motions induce lifting.Upper level motions induce lifting.


C. THUNDERSTORM TYPESC. THUNDERSTORM TYPES Single-Cell ThunderstormsSingle-Cell Thunderstorms

– ““Air Mass” ThunderstormsAir Mass” Thunderstorms

– Orographic ThunderstormsOrographic Thunderstorms Frontal ThunderstormsFrontal Thunderstorms Squall-Line ThunderstormsSquall-Line Thunderstorms Mesoscale Convective Complexes (MCC)Mesoscale Convective Complexes (MCC) Multiple-Cell ThunderstormsMultiple-Cell Thunderstorms


D. THUNDERSTORM CLIMATOLOGYD. THUNDERSTORM CLIMATOLOGY

Geographical & Seasonal DistributionGeographical & Seasonal Distribution Time of DayTime of Day Duration of ThunderstormsDuration of Thunderstorms Reported Thunderstorm IntensitiesReported Thunderstorm Intensities


Thunderstorm ClimatologyThunderstorm Climatology

See Fig. 13.9, Moran & Morgan (1997)See Fig. 13.9, Moran & Morgan (1997)


E. CHARACTERISTICS OF E. CHARACTERISTICS OF THUNDERSTORMSTHUNDERSTORMS

The Thunderstorm Cell ModelThe Thunderstorm Cell Model Life Cycle of a Non-Severe Life Cycle of a Non-Severe

Thunderstorm CellThunderstorm Cell– Where…Where…


Cumulus Stage in thunderstorm life cycleCumulus Stage in thunderstorm life cycle See Fig. 13.2a, Moran & Morgan (1997)See Fig. 13.2a, Moran & Morgan (1997)


Mature Stage in thunderstorm life cycleMature Stage in thunderstorm life cycle See Fig. 13.2b, Moran & Morgan (1997)See Fig. 13.2b, Moran & Morgan (1997)


Dissipating Stage in thunderstorm life cycleDissipating Stage in thunderstorm life cycle See Fig. 13.2c, Moran & Morgan (1997)See Fig. 13.2c, Moran & Morgan (1997)


F. SEVERE THUNDERSTORMSF. SEVERE THUNDERSTORMS Official Criteria for Severe WeatherOfficial Criteria for Severe Weather

– Large hailLarge hail (3/4 inch or large diameter)(3/4 inch or large diameter);;

– and/orand/or

– Damaging WindsDamaging Winds (surface wind gusts of 58 mph (surface wind gusts of 58 mph oror greater) greater)..

Unofficial Criteria for Severe WeatherUnofficial Criteria for Severe Weather– Tornadoes, Heavy Precipitation, Flash Tornadoes, Heavy Precipitation, Flash

Flooding, Deadly LightningFlooding, Deadly Lightning


Vertical Cross section of Severe Vertical Cross section of Severe ThunderstormThunderstorm



Ingredients for severe thunderstorm episodeIngredients for severe thunderstorm episodeSee Fig. 13.13, Moran & Morgan (1997)See Fig. 13.13, Moran & Morgan (1997)


F. SEVERE THUNDERSTORMS F. SEVERE THUNDERSTORMS (con’t.)(con’t.)

Types of Severe ThunderstormsTypes of Severe Thunderstorms Structure of Severe ThunderstormsStructure of Severe Thunderstorms Synoptic Situations Favoring Severe Synoptic Situations Favoring Severe

Thunderstorm WeatherThunderstorm Weather Movement of Severe Thunderstorm Movement of Severe Thunderstorm

CellsCells


NWS Watches & WarningsNWS Watches & Warnings

Severe thunderstorm Severe thunderstorm watchwatch– Issued by National Weather Service to Issued by National Weather Service to

alert public that conditions are favorable alert public that conditions are favorable for development of severe thunderstorms for development of severe thunderstorms (large hail &/or high winds).(large hail &/or high winds).

Severe thunderstorm Severe thunderstorm warningwarning – Issued by National Weather Service to Issued by National Weather Service to

warn public that a severe thunderstorm warn public that a severe thunderstorm has been sighted by storm spotters or has has been sighted by storm spotters or has been indicated by radar.been indicated by radar.


Hail ClimatologyHail Climatology



Tornado ClimatologyTornado Climatology



Cross-section of a Cross-section of a thunderstorm cellthunderstorm cell

atm ocn 100 - summer 2002 lectures 32 & 33

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