GEO - Severe Weather Quiz

Quiz 5

Sing Cell Thunderstorm

• Weak updraft (non-severe or Strong updraft)

• Slight threat

• Weakest

Multicell Cluster Thunderstorm

• Weak updraft (non-severe or Strong updraft)

• Moderate threat

• 2nd weakest

Multicell Line Thunderstorm

• Weak updraft (non-severe or Strong updraft)

• Moderate threat

• 2nd Strongest

Supercell Thunderstorm

• Intense updraft (Almost always severe)

• Mesocyclone present

• High threat

• Strongest

Ingredients for a thunderstorm

• Lift from

  • Cold/warm front

  • Gust front

  • Daytime heating

• Low-level moisture

• Instability

• Wind shear

Severe thunderstorms needs one or more of the following:

• Winds stronger than 58 mph

• Hailstones larger than 0.75 in

• Tornado

Single Cell or “Pulse”

Moves with mean environmental wind over 5-7 km.

30- 60 minute duration.

Rainfall can be moderate to heavy, small hail is possible.

Vertical wind shear is small.

Form in very weak shear environments with new storms forming in an unorganized manner

Can be severe at dissipation

Multi Cell Clusters

Cluster of 2-4 storms

Feed off gust front

Moderate unidirectional shear

Moderate instability

Follow mean 700 – 500 mb flow

Mesoscale Convective Complex

May – Aug (86%)

Multi celled storms “gone wild”

Oval shaped

Cloud shield

< -32°C = 100,000km2

< -52°C = 50,000 km2

Last at least 6 hours

Usually night events

Flash floods

Hail

Squall Lines

Linear multi cell storms

Frontal or pre-frontal

Vertical tilt increases severity

Moist low level S or SE inflow

Mid level flow >25 knots and ┴ to low level flow

Supercell

Balanced updraft and downdraft

Low level mesocyclogenesis more likely

Moderate hook echo

Tornadoes are common

Lightning and thunder

Lightning = flashes of light caused by enormous electrical discharges

Superheats the air abruptly resulting in enormous shock waves

• thunder

Types of lightning

Within cloud

Cloud-to-cloud

Cloud-to-air

Cloud-to-ground

Negative lightning

Positive lightning

Hail

Ice pellets

Only occur within cumulonimbus clouds

The longer a frozen pellet stays aloft in a cloud, the larger the hail can be

“Wet-bulb zero” height important

Tornadoes

As cumulonimbus clouds rise high into the troposphere, the bottom winds move slow due to surface friction, but the upper winds move fast

Results in rotation of air parallel to the ground

Updrafts or downdrafts can cause the vortex to become vertical

Hurricane characteristics

Sustained winds of 120 km or more

Sea level pressure < than 990 mb

Varying sizes but cloud shield usually > 400 km diameter

Warm tropical waters > 27°C (~80)

Atlantic Season

• June – November

• Peak: Mid August – Early October

Hurricane movement & dissipation

Controlled by large surface pressure systems

• Steered by orientation and position of subtropical high

Controlled by upper-level flow

Vary by time of year

Will dissipate over land or colder water

Hurricane Development

Coriolis Force

Atlantic Formation usually between 10 – 20°N

Water above 27°C

Little wind shear

Levels of storm

One closed isobar: Tropical Depression (receives number)

60 km/h winds:
Tropical Storm   (receives name)

120 km/h winds: Hurricane

These vary worldwide

Problems with the Saffir Simpson Scale

Pre-landfall Warning Scale

• Was the storm as strong as advertised?

Uniform Rating

Focuses on wind speed and accompanying surge

• SURGE discrepancies

Duration?

• Size?

Precipitation?

Gusts

• Surface friction, topography

How is tornado strength rated?

By examining the damage caused

What is one difference between a Tornado WATCH and a Tornado WARNING?

WATCH is issued by NOAA Storm Prediction Center

Rank the thunderstorm types by potential lethality to humans (lowest number is most dangerous)

1. supercells, 2. squall lines, 3. airmass or cluster

The main hazards associated with air mass thunderstorms are?

flash flooding and lightning

Air mass thunderstorms are common in what season?

summer

The most common type of severe weather in Alabama

squall lines

What is the most severe type of thunderstorm

supercells