THUNDERSTORMSAnd SEVERE WEATHER SEVERE WEATHER

What’s in a Name? Cyclone refers to the circulation around a low-pressure center Cyclone refers to the circulation around a low-pressure center Hurricanes / Typhoons Hurricanes / Typhoons Midlatitude cyclones Midlatitude cyclones Tornadoes Tornadoes

Thunderstorms Thunderstorms generate lightning, thunder, winds, and hail Thunderstorms generate lightning, thunder, winds, and hail There are two types of thunderstorms. There are two types of thunderstorms. Air-mass thunderstorms are associated with warm, humid air that rises in unstable environments creating cumulonimbus (Cb) clouds, and is typical of mT air masses. Air-mass thunderstorms are associated with warm, humid air that rises in unstable environments creating cumulonimbus (Cb) clouds, and is typical of mT air masses. Widespread and Severe thunderstorms may produce high winds, hail, flash floods, and tornadoes. Widespread and Severe thunderstorms may produce high winds, hail, flash floods, and tornadoes. They are the result of uneven heating, aided by frontal lifting, and diverging winds. They are the result of uneven heating, aided by frontal lifting, and diverging winds.

Ingredients for T-Storms 1) Moisture 1) Moisture 2) Instability 2) Instability 3) Source of Lift 3) Source of Lift Buoyant air rising due to sunshine Buoyant air rising due to sunshine Air forced over hilly terrain Air forced over hilly terrain Fronts & low pressure systems Fronts & low pressure systems

Third: A Source of Lift VERTICAL LIFT CAN BE PRODUCED IN THREE DIFFERENT WAYS: VERTICAL LIFT CAN BE PRODUCED IN THREE DIFFERENT WAYS: 3a) Buoyant air rising due to sunshine 3a) Buoyant air rising due to sunshine 3b) Air forced over hilly terrain 3b) Air forced over hilly terrain 3c) Fronts & low pressure systems 3c) Fronts & low pressure systems

First: You need moisture

Second: You need VERTICAL INSTABILITY

Buoyant Unstable Air Parcels Due to Sunshine (uneven surface heating) resulting in Thermals

And/or Forced Accent due to upslope wind flow

Fronts and Low Pressure Systems FRONTALWEDGING

The entire ‘life-cycle’ for typical air mass T-storms can take less than 30 minutes! These types of T-storms tend to occur most often in Mountainous regions, such as the Rockies and the Appalachians – but are also fairly common in the deep south during the summer when temperatures and humidity are quite high most of the time These types of T-storms tend to occur most often in Mountainous regions, such as the Rockies and the Appalachians – but are also fairly common in the deep south during the summer when temperatures and humidity are quite high most of the time

Air-Mass Thunderstorms Cumulus stage: Cumulus stage: A cumulonimbus tower develops as water vapor moves from the surface to greater heights. A cumulonimbus tower develops as water vapor moves from the surface to greater heights. Downdrafts form via entrainment (influx of cool dry air). Downdrafts form via entrainment (influx of cool dry air).

Air-Mass Thunderstorms Mature stage: Mature stage: This is the most intense phase. This is the most intense phase. This results in heavy rain and possibly small hail This results in heavy rain and possibly small hail Cool downdrafts exist next to updrafts. Cool downdrafts exist next to updrafts.

Air-Mass Thunderstorms Dissipation stage: Dissipation stage: As the local heating is eliminated cool downdrafts, no additional moisture is lifted into the storm – and the rain lightens As the local heating is eliminated cool downdrafts, no additional moisture is lifted into the storm – and the rain lightens The T-storm looses it’s heat/moisture source, so it weakens and eventually dissipates The T-storm looses it’s heat/moisture source, so it weakens and eventually dissipates

Initial Development is Moderate Cumulus Tops: 6,000 – 12,000 feet

Further Development is Towering Cumulus Tops: 12,000 – 25,000 feet

Mature Development is Cumulonimbus Tops: 25,000 – 65,000 feet Mature Development is Cumulonimbus Tops: 25,000 – 65,000 feet LOWER HEIGHTS GENERALLY AT HIGHER LATITUDES AND/OR WINTER

What causes LIGHTNING and THUNDER?

Lightning and Thunder Lightning strokes: Lightning strokes: The flash (total discharge) lasts a few tenths of a second. The flash (total discharge) lasts a few tenths of a second. It is what we see and it contains multiple strokes. It is what we see and it contains multiple strokes. The leader is ‘ionized’ air, which firsts forms a conductive path, and then… The leader is ‘ionized’ air, which firsts forms a conductive path, and then… A step leader extends earthward in a short, nearly invisible burst A step leader extends earthward in a short, nearly invisible burst The return stroke extends upward from ground to cloud and is what we REALLY see as lightning! The return stroke extends upward from ground to cloud and is what we REALLY see as lightning!

Thunder: Thunder: The air within/next to the lightning stroke is rapidly heated to as much as 50,000° F The air within/next to the lightning stroke is rapidly heated to as much as 50,000° F The air expands explosively, which produces sonic wave that travels at 1,000 Ft/second (hence the ‘5’ second rule’) The air expands explosively, which produces sonic wave that travels at 1,000 Ft/second (hence the ‘5’ second rule’) If lightning is more than 15 miles away, thunder is usually not heard If lightning is more than 15 miles away, thunder is usually not heard Lightning and Thunder

Lightning 50,000° !

How does lightning work? Earth has a Positive Charged

Positive Charges Are Dragged Through Tall Objects A ‘Leader’ is created between the cloud and ground The ‘step Leader‘ then forms directly between the cloud and the ground forming the path for the lightning stroke

Negative Charges Become Attracted and Strike Object

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

Lightning Kills!

Where do T-storms occur?

Three Regions, Three Types!

A: Very wet, slow moving T-Storms / Lots of lightning Rarely ‘Severe’ EXCEPT in Spring A A

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

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

Severe Thunderstorms and Tornadoes HAILTORNADOES FLASH FLOODS FLOODS UnspeakableDestruction

Severe Thunderstorms Severe thunderstorms: Severe thunderstorms: Heavy downpours Heavy downpours Flash flooding Flash flooding STRONG, ‘Straight Line’ wind gusts STRONG, ‘Straight Line’ wind gusts Large Hail, lightning Large Hail, lightning Wind shear Wind shear Downdraft preceding (gust front) Downdraft preceding (gust front) Can lead to Super Cell Thunderstorms Can lead to Super Cell Thunderstorms

Airmasses Collide produce HORIZONTAL INSTABILITY

Several Ingredients Come Together in Tornado Alley

Hail Forms Above Freezing Level

Some Updrafts Can Lead to Large Hail but No Rain!

Quarter size hailstones Marble size hailstones

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

Idealized Weather Map Showing ‘Squall Line’ L

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

Cumulonimbus Cloud

Roll Clouds along a Gust Front

Microburst Downdraft

Microburst - Downward burst of cooler air

T-STORMS EXTREMELY DANGEROUS TO AIRPlANES

Note where Downbursts originates from

Supercell Thunderstorms

Supercells Supercells These storms can produce extremely dangerous weather. These storms can produce extremely dangerous weather. They consist of a single, powerful cell that can extend to heights of 60,000 ft or more!!! They consist of a single, powerful cell that can extend to heights of 60,000 ft or more!!! The clouds can measure miles in diameter. The clouds can measure miles in diameter. Mesocyclone: Mesocyclone: Vertical winds may cause the updraft to rotate, which forms a column of cyclonically rotating air. Vertical winds may cause the updraft to rotate, which forms a column of cyclonically rotating air. Tornadoes often form. Tornadoes often form.

Supercell Thunderstorms Squall lines: Squall lines: Squall lines are narrow bands of thunderstorms. Squall lines are narrow bands of thunderstorms. cT air is pulled into the warm sector of a midlatitude cyclone. cT air is pulled into the warm sector of a midlatitude cyclone. Mammatus skies sometimes precede squall lines. Mammatus skies sometimes precede squall lines. These can also form along a dryline, where there is an abrupt change in moisture. These can also form along a dryline, where there is an abrupt change in moisture.

Supercell Thunderstorms Squall lines Squall lines Mammatus L

SUPERCELL THUNDERSTORMS Inside the thunderstorm: SUPERCELL THUNDERSTORMS Inside the thunderstorm:

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