THUNDERSTORMTHUNDERSTORMS S

AndAnd SEVERE SEVERE

WEATHERWEATHER

What’s in a Name?What’s in a Name?

CycloneCyclone refers to the circulation refers to the circulation around a around a low-pressure centerlow-pressure center

Hurricanes / TyphoonsHurricanes / Typhoons Midlatitude cyclonesMidlatitude cyclones TornadoesTornadoes

ThunderstormsThunderstorms Thunderstorms generateThunderstorms generate lightning, lightning,

thunder, winds, and hailthunder, winds, and hail There are two types of thunderstorms.There are two types of thunderstorms.

Air-mass thunderstormsAir-mass thunderstorms are associated are associated with warm, humid air that rises in with warm, humid air that rises in unstable environments creating unstable environments creating cumulonimbus (Cb) clouds, and is typical cumulonimbus (Cb) clouds, and is typical of mT air masses.of mT air masses.

Widespread and Severe thunderstormsWidespread and Severe thunderstorms may produce high winds, hail, flash may produce high winds, hail, flash floods, and tornadoes.floods, and tornadoes. They are the result of uneven heating, aided They are the result of uneven heating, aided

by by frontal lifting, and diverging windsfrontal lifting, and diverging winds..

Ingredients for T-StormsIngredients for T-Storms

1) Moisture1) Moisture 2) Instability2) Instability 3) Source of Lift3) Source of Lift

Buoyant air rising due to sunshineBuoyant air rising due to sunshine Air forced over hilly terrainAir forced over hilly terrain Fronts & low pressure systemsFronts & low pressure systems

Third: A Source of LiftThird: A Source of Lift

VERTICAL LIFT CAN BE PRODUCED VERTICAL LIFT CAN BE PRODUCED IN THREE DIFFERENT WAYSIN THREE DIFFERENT WAYS::

3a) Buoyant air rising due to 3a) Buoyant air rising due to sunshinesunshine

3b) Air forced over hilly terrain3b) Air forced over hilly terrain 3c) Fronts & low pressure systems3c) Fronts & low pressure systems

First: You need moistureFirst: You need moisture

Second: You need Second: You need VERTICAL INSTABILITY VERTICAL INSTABILITY

Buoyant Unstable Air Parcels Buoyant Unstable Air Parcels Due to Sunshine (uneven Due to Sunshine (uneven

surface heating) resulting in surface heating) resulting in ThermalsThermals

And/or Forced Accent due And/or Forced Accent due to upslope wind flowto upslope wind flow

Fronts and Low Pressure Fronts and Low Pressure SystemsSystems

FRONTAL FRONTAL WEDGINGWEDGING

The entire ‘life-cycle’ for The entire ‘life-cycle’ for typical air mass T-storms can typical air mass T-storms can

take less than 30 minutes!take less than 30 minutes! These types of T-storms tend to occur These types of T-storms tend to occur

most often in Mountainous regions, most often in Mountainous regions, such as the Rockies and the such as the Rockies and the Appalachians – but are also fairly Appalachians – but are also fairly common in the deep south during the common in the deep south during the summer when temperatures and summer when temperatures and humidity are quite high most of the humidity are quite high most of the timetime

Air-Mass ThunderstormsAir-Mass Thunderstorms

Cumulus stage:Cumulus stage: A cumulonimbus tower A cumulonimbus tower

develops as water vapor develops as water vapor moves from the surface moves from the surface to greater heights.to greater heights.

Downdrafts form via Downdrafts form via entrainmententrainment (influx of (influx of cool dry air).cool dry air).

Air-Mass ThunderstormsAir-Mass Thunderstorms

Mature stage: Mature stage: This is the most This is the most

intense phase.intense phase. This results in This results in

heavy rain and heavy rain and possiblypossibly small hail small hail

Cool downdrafts Cool downdrafts exist next to exist next to updrafts.updrafts.

Air-Mass ThunderstormsAir-Mass Thunderstorms Dissipation stage: Dissipation stage:

As the local heating As the local heating is eliminated cool is eliminated cool downdrafts, no downdrafts, no additional moisture additional moisture is lifted into the is lifted into the storm – and the rain storm – and the rain lightens lightens

The T-storm looses The T-storm looses it’s heat/moisture it’s heat/moisture source, so it source, so it weakens and weakens and eventually eventually dissipatesdissipates

Initial Development is Moderate Initial Development is Moderate CumulusCumulus

Tops: 6,000 – 12,000 feet Tops: 6,000 – 12,000 feet

Further Development is Towering Further Development is Towering CumulusCumulus

Tops: 12,000 – 25,000 feetTops: 12,000 – 25,000 feet

Mature Development is CumulonimbusMature Development is CumulonimbusTops: 25,000 – 65,000 feetTops: 25,000 – 65,000 feet

LOWER HEIGHTS GENERALLY AT HIGHER LATITUDES

AND/OR WINTER

What causes LIGHTNING What causes LIGHTNING and THUNDER?and THUNDER?

Lightning and ThunderLightning and Thunder

Lightning strokes:Lightning strokes: The The flashflash (total discharge) lasts a few (total discharge) lasts a few

tenths of a second. tenths of a second. It is what we see and it contains multiple It is what we see and it contains multiple

strokes.strokes. The The leaderleader is ‘ionized’ air, which firsts is ‘ionized’ air, which firsts

forms a conductive path, and then…forms a conductive path, and then… A A step leaderstep leader extends earthward in a extends earthward in a

short, nearly invisible burstshort, nearly invisible burst The The return strokereturn stroke extends upward from extends upward from

ground to cloud and is what we REALLY ground to cloud and is what we REALLY see as lightning!see as lightning!

Thunder:Thunder: The air within/next to the lightning The air within/next to the lightning

stroke is rapidly heated to as much as stroke is rapidly heated to as much as 50,00050,000° F° F

The air expands explosively, which The air expands explosively, which produces sonic wave that travels at produces sonic wave that travels at 1,000 Ft/second (hence the ‘5’ second 1,000 Ft/second (hence the ‘5’ second rule’)rule’) If lightning is more than 15 miles If lightning is more than 15 miles

away, thunder is away, thunder is usuallyusually not heard not heard

Lightning and ThunderLightning and Thunder

Lightning 50,000Lightning 50,000° !° !

How does lightning How does lightning work?work?Earth has a Positive Earth has a Positive

ChargedCharged

Positive Charges Are Dragged Positive Charges Are Dragged Through Tall ObjectsThrough Tall Objects

A ‘Leader’ is A ‘Leader’ is created between created between the cloud and the cloud and groundground

The ‘step The ‘step Leader‘ then Leader‘ then forms directly forms directly between the between the cloud and the cloud and the ground forming ground forming the path for the the path for the lightning strokelightning stroke

Negative Charges Negative Charges Become Attracted and Become Attracted and

Strike ObjectStrike Object

The process repeats The process repeats itself until most of the itself until most of the negative charges at negative charges at the bottom of the the bottom of the cloud is dissipatedcloud is dissipated

Lightning Kills!Lightning Kills!

Where do T-storms Where do T-storms occur?occur?

Three Regions,Three Regions,Three Types!Three Types!

A: Very wet, slow moving A: Very wet, slow moving T-Storms / Lots of lightning T-Storms / Lots of lightning

Rarely ‘Severe’ EXCEPT in Spring Rarely ‘Severe’ EXCEPT in Spring

A

AA

B) Highly Elevated.. Lots of Hail B) Highly Elevated.. Lots of Hail Not a lot of RainfallNot a lot of Rainfall

BB

AA

C) Lots of Rain, Hail & Wind Capable of Tornadoes!C) Lots of Rain, Hail & Wind Capable of Tornadoes!RECHECK THESE LINBKGS AND IUNFO!!! RECHECK THESE LINBKGS AND IUNFO!!!

http://www.youtube.com/watch?v=jVTs55W3Iag

http://www.youtube.com/watch?v=Kj47equXqU0

CC

AA

BB

Severe Thunderstorms and Severe Thunderstorms and TornadoesTornadoes

HAILHAIL TORNADOESTORNADOES

FLASHFLASH FLOODSFLOODS

UnspeakableUnspeakableDestructionDestruction

Severe ThunderstormsSevere Thunderstorms Severe thunderstorms:Severe thunderstorms:

Heavy downpoursHeavy downpours Flash floodingFlash flooding STRONG, ‘Straight Line’ wind gustsSTRONG, ‘Straight Line’ wind gusts Large Hail, lightningLarge Hail, lightning Wind shearWind shear Downdraft preceding (gust front)Downdraft preceding (gust front) Can lead to Super Cell ThunderstormsCan lead to Super Cell Thunderstorms

Airmasses Collide produce Airmasses Collide produce HORIZONTAL INSTABILITY HORIZONTAL INSTABILITY

Several Ingredients Several Ingredients Come Together in Come Together in

Tornado AlleyTornado Alley

Hail Forms Above Hail Forms Above Freezing LevelFreezing Level

Some Updrafts Can Lead Some Updrafts Can Lead to Large Hail but No to Large Hail but No

Rain!Rain!

Quarter sizeQuarter sizehailstoneshailstones

Marble sizeMarble sizehailstoneshailstones

Squall Lines Develop along Strong Squall Lines Develop along Strong Cold Fronts and ‘Drylines’Cold Fronts and ‘Drylines’

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Idealized Weather Idealized Weather Map Showing Map Showing ‘Squall Line’‘Squall Line’

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Satellite Image of Strong Squall Line from Dakotas southward to New Mexico

Cumulonimbus CloudCumulonimbus Cloud

Cumulonimbus CloudCumulonimbus Cloud

Roll Clouds along a Gust Front

Microburst DowndraftMicroburst Downdraft

Microburst - Downward Microburst - Downward burst of cooler airburst of cooler air

T-STORMS EXTREMELY T-STORMS EXTREMELY DANGEROUS TO DANGEROUS TO

AIRPlANESAIRPlANES

Note where Downbursts Note where Downbursts originates fromoriginates from

Supercell ThunderstormsSupercell Thunderstorms

Supercell ThunderstormsSupercell Thunderstorms Supercells Supercells

These storms can produce extremely These storms can produce extremely dangerous weather.dangerous weather. They consist of a single, powerful cell that can They consist of a single, powerful cell that can

extend to heights of 60,000 ft or more!!!extend to heights of 60,000 ft or more!!! The clouds can measure 50-150 miles in The clouds can measure 50-150 miles in

diameter.diameter.

Mesocyclone:Mesocyclone: Vertical winds may cause the updraft to Vertical winds may cause the updraft to

rotate, which forms a column of cyclonically rotate, which forms a column of cyclonically rotating air.rotating air.

Tornadoes often form.Tornadoes often form.

Supercell ThunderstormsSupercell Thunderstorms

Squall lines:Squall lines: Squall lines are narrow bands of Squall lines are narrow bands of

thunderstorms.thunderstorms. cT air is pulled into the warm sector of a cT air is pulled into the warm sector of a

midlatitude cyclone.midlatitude cyclone. Mammatus skies sometimes precede Mammatus skies sometimes precede

squall lines.squall lines. These can also form along a dryline, These can also form along a dryline,

where there is an abrupt change in where there is an abrupt change in moisture.moisture.

Supercell ThunderstormsSupercell Thunderstorms

Squall linesSquall lines

Mammatus

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SUPERCELL THUNDERSTORMSSUPERCELL THUNDERSTORMSInside the thunderstorm:Inside the thunderstorm:

http://www.youtube.com/watch?v=36vGiE5JQzs&feature=relatedhttp://www.youtube.com/watch?v=MO7W5iP46Ms&feature=related

END PART END PART 11