Meteorology Today CH 14

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Thunderstorms

A single or cluster of cumulonimbus clouds that produce lightning and thunder. May contain heavy rains or even gusty winds

True or False: Thunderstorms occur as warm, humid air rises in an unstable environment

True

Air-mass Thunderstorms

Scattered summertime thunderstorms that tend to develop in warm, maritime tropical air masses away from weather fronts (in FL)

Does a thunderstorm produce hail?

Yes - sometimes. Cumulonimbus clouds are the only ones capable of producing hail

Cumulus stage of a thunderstorm

As humid air rises, it cools and some of its water vapor condenses into a single cumulus cloud or cluster of clouds

True or false: During the Mature stage is when large amounts of latent heat is released - keeping the inside of the cloud warmer than the surrounding air

FALSE! This happens in the Cumulus stage

Entrainment

the process of drier air being drawn into the cloud

Downdraft

When some cold air that's heavier begins to descend

Cell

Downdrafts and updrafts constitute this

Mature Thunderstorm

Makes the appearance of the downdraft and the storm cell

True or False: A thunderstorm is most intense in its Cumulus stage?

FALSE - its most intense in its Mature stage.

At which stage does the cold air take on its anvil shape where the cloud itself can reach altitudes of over 40K feet?

Mature stage

Ordinary Cell Thunderstorm

Tend to form in a region where there is limited wind shear - that is where the wind speed and wind direction do not abruptly change with increasing height above the surface

Another name for the first stage

Growth stage or cumulus stage

True or false: The tilt of the anvil is an indication of the direction of which way the storm moves

True

How many minutes into the mature stage does the storm begin to dissipate?

15 minutes to 1/2 hr

Dissipating stage

3rd and final stage of a thunderstorm. Downdrafts occur - light precipitation now falls, most of the cloud particles in the lower half of the storm have evaporated.

Vergal

Rain or drizzle evaporated before touching the ground

Fall streak

Snow or ice that goes from solid to gas before reaching the ground <--sublimate

Severe Thunderstorms

Capable of producing large hail (3/4"), strong gusty winds (50mph or more), flash floods and tornadoes.

What is the #1 sever weather killer?

Flash flooding

True or false: Many storms do not have tilted updrafts

True

The updrafts may be strong, up to ______ knots, and precipitation size particles do not have time to form

100

Why does the cooling effect only last a short while after the storm has dissipated?

After a storm, the air temp usually rises; and as the moisture from the rainfall evaporates into the air, the humidity increases - sometimes to a level where it feels even more oppressive after the storm than before.

Multicell Thunderstorm

Thunderstorms that contain a number of cells, each in a different stage of development

Overshooting top

If the updrafts are extremely strong, they may do this well in to a stable stratosphere -possibly to more than 60K feet! Hail also can grow to very large sizes.

What is the main difference between a roll cloud and a funnel cloud?

Roll clouds spin horizontally & Funnel clouds spin vertically

Gust front

boundary that separates the cold downdraft from the warm surface. Literally looks like a cold front, to an observer on the ground

With the passage of a gust front, surface pressure may rise rapidly and create a small area of high pressure called

a mesohigh

Shelf Cloud

As warm, moist air rises along the forward edge of the gust front, this may form; AKA barber pole cloud

Roll Cloud

appear to spin about a horizontal axis - elongated and ominous looking

Outflow boundary

A surface boundary formed by the horizontal spreading of cool air that originated inside a thunderstorm

Downbursts

strong localized winds that hit the ground and are spread out horizontally (like water from your faucet hitting the sink)

What are the two types of downbursts?

Microburst & Macroburst

Microburst

a downburst with winds extending ONLY 4km or less - very strong winds can occur

Macroburst

a downburst wind extending OVER 4km

Which type of downburst can evolve into a gust front?

microburst

Heat bursts

Sudden, warm downbursts that originate high up in the thunderstorm

Microbursts are often accompanied with ____ _____, which is a rapid change in wind speed OR wind direction

Wind Shear

Name of alert system setup around airports

LLWAS - Low Level Wind Shear Alert Systems

LLWAS detect what type of downbursts?

microbursts - but only AFTER they hit the ground

True or False: Microbursts can produce only isolated showers, in which they may or may not contain thunder?

True

Supercell storms

single, violently rotating updraft, enormous storms that can maintain themselves for hours. 90 knot winds, grapefruit size hail and many tornadoes MAY form - mostly in the springtime.

Squall line

forms as a line of multicell thunderstorms. sometimes you can see them right along a cold front or in the warm air some 100-300km ahead of it

These _______________________ are the most severe type of squall line

pre-frontal squall line thunderstorms

Ordinary squall lines

Squall lines that exhibit weaker updrafts and downdrafts tend to be more shallow than pre- frontal squall lines and usually have shorter life spans.

bow echos

the shape of a squall line that often produces damaging surface winds near the center of the bow. Sometimes the left (northern) end of the bow will develop into cyclonic rotation and produce a tornado

Dryline

is a narrow zone where there is a sharp horizontal change in moisture.

Dryline is AKA

dew-point fronts

Severe storms are often associated with ______

Flash floods

Flash floods often occur with ....

spring snow melt, tropical storms, downburst from a strong thunderstorm

A large convective weather system that contains a number of individual thunderstorms that will grow in size is called a

MMC - mesoscale convective complex

mesocyclone

rotating air column on the south side of the storm, usually 5 - 10km across.

True or false: the rotating updraft associated with the mesocyclone is so strong that precipitation cannot fall thru it

True - this produces a rain free base beneath this updraft

Wall cloud

rotating cloud that may descend from the base of the storm if low-level humid air is drawn into the updraft.

Most thunderstorms move in the direction of the _______ level winds

upper

Thunderstorms rarely occur is _____ climates

dry - like polar or desert

The least number of thunderstorms are found in what area

Pacific Coastal

Why does the South Eastern portions of the country have more annual thunderstorms, but the Western Great Plains have more hail?

Because its colder there - hail needs cold air / front

The average number of days each year on which thunderstorms are observed throughout the US

Most in FL - lessening up as you move north west

The average number of days each year on which hail is observed throughout the US

mostly in CO, NM, NV - dissipates in a circle moving in all directions

Lightning

a discharge of electricity - can be 5x as hot as the sun

Thunder

extreme heat causes air to expand explosively, initiating a shockwave that becomes a booming sound wave

Which do we see / hear first? Lightning or thunder

See lightning then hear thunder

A sound occasionally mistaken for thunder is a

sonic boom

Ratio of lightning to thunder

1:5; meaning count to 5 = 1 mile. So if you have 30 seconds = 6 miles

Can lightning occur without thunder?

No - there is actually thunder, but the atmosphere refracts (bends) and attenuates the sound waves.

True or false: for lightning to occur, separate regions containing opposite electrical charges must exist within a cumulonimbus cloud

True

True or false: When falling precipitation collides with smaller particles, the larger precipitation particles become negatively charged and the smaller particles, positively charged

True

A Lightning stroke involves a ______, which is an initial charge of electrons that proceeds intermittently toward the ground in a series of 'steps' in a cloud to ground lightning strike

stepped leader

Return stroke

the downward flow of electrons establishes the bright channel of upward propagating current. This all happens in 1/10,000 of a second.

There is a subsequent leader called a ____ that proceeds from the cloud along the same channel as the original stepped leader - about 4/100ths of a second later

dart leader

Typically lightning will have ____ leaders - each followed by a return stroke. All of this happening in less than a second

3-4

Negative to ground vs positive to ground

we see neg as a flicker and pos as a flash

which charged lightning is most common with supercell thunderstorms?

positive

forked lightning

most common - dart leader moving towards the ground which deviates from the original path by the stepped leader

Ribbon lightning

this occurs as winds move the ionized channel between the return stroke

Bead lightning

occurs when the lightning channel breaks up or appears to break up. exact cause is not knows, but stroke may be partially obscured by clouds or falling rain

fulgurite

when lightning enters sandy soil, high temperatures of the stroke may fuse sand particles together forming these tubes

on a radar-type map of lightning - red and blue hits are shown. which are old, which are new?

blue - old; red - new

Tornado

rapidly rotating winds that blow around a small area of intense low pressure with a circulation that reaches the ground

funnel cloud

tornado whose circulation has not reached the ground

The size of tornadoes are between 300 - 2000 ft in diameter and tend to move ___ to ___ at around ___ knots due to the steering of SW winds (normally)

SW to NE at around 20-40

Tornado life cycle

dust whirl -> organizing -> mature -> shrinking ->decay

tornado outbreak

when a large # of tornadoes (6 or more) form over a particular region

Around ___% fatalities each year from tornadoes occur in mobile homes

45

what type of cloud is usually associated with a tornado?

wall cloud

Water spout

when a tornado touches water

tornado watch

issued when tornadoes are likely to form during the next few hours

tornado warning

once a tornado is spotted - its real and its a warning - seek shelter immediately

Fujita Scale

scale for classifying tornadoes according to their rotational wind speed - cannot classify until assessing damage afterwards

MOST tornadoes are in the line of F_ and F_ - maybe one per year will reach F_

F0 - F1 - are most - once a year it can be F5

Multi-vortex

causes the most damage - have smaller whirls that rotate within them - exceeding 180 knots

suction vortices

smaller whirls inside a multi-vortex tornado

Most tornadoes in US occur in the 'tornado belt' of the Central Plains - stretches from TX to NE

True

Time frame for 3/4 of the development (Months)

March - July

Which month has the greatest # of tornadoes?

May

Which month has the most violent tornadoes?

April

What time in the afternoon is the most frequent time for the tornadoes to hit?

4-6pm

When facing an onrushing tornado, the strongest winds will be coming from your _____

left

The total wind speed of a tornado is _____ on one side than on the otehr

greater

Tornado is moving from SW to NE - the strongest winds are 90 degrees to the ____ of movement of the storm

right

The weakest winds are 90 degrees to the ___ of movement of the storm

left

bounded weak echo region (BWER)

the region inside the supercell where radar is unable to detect precipitation

while precipitation is drawn into a cyclonic spiral around the mesocyclone, the rotating precipitation may unveil itself in the shape of a hook called

hook echo

water spouts

rotating column of air that is connected to a cumuliform cloud over a large body of water.

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