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106 terms

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.