UIUC Atms 120: Exam 3 (Final)

if T of parcel < T of environment

=stable (no t-storms)

if T of parcel > T of environment

=unstable (like the hot air balloon)

convective available potential energy (CAPE)

A measure of the potential intensity of thunderstorms

Are cars safe from lightning? What about airplanes?

Yes

What is heat lightning? Is it real?

a storm that is so far away that you can only see the lightning but not hear the thunder; not real-it is actually "sheet lightning"

What are mammatus clouds? are they dangerous?

cellular pattern of pouches hanging from the base of a cloud. looks like bumps; they are not dangerous

gust front

cool blast of air that formed in the downdraft of the thunderstorm

updraft

current of rising air -cannot have a thunderstorm without an updraft -latent heat release due to condensation in updraft powers thunderstorm

On what basis are tornadoes rated?

damage; tornado winds usually not measured directly

What is a multiple vortex tornado? How are they different than regular tornadoes?

one supercell with multiple tornadoes; the tornado breaks into multiple suction vortices

Why is moisture important to thunderstorm formation?

warm moist air is fuel for the storm; Td at least 60 degrees F

What is the difference between a watch and warning?

watch=conditions are favorable for severe weather warning=sever weather is happening now

How are lightning and thunder related? How is thunder created?

when a lightning bolt travels from the cloud to the ground it opens up a channel. Once the light is gone the air collapses back in a creates a sound wave that we hear as thunder

How does the relative humidity of air change as it rises and sinks? Why?

hot air expands, and rises; cooled air contracts--gets denser--and sinks; the ability to hold water depends on its temperature...when air holds as much water vapor as it can for a given temperature

What is the supercell spectrum? Which type of supercell is the most prolific tornado producer?

includes classic supercell, heavy-precipitation supercells, & low-precipitation supercells; classic supercell

What is the life cycle of a tornado? Why do they dissipate?

lifetime ranges from seconds to an hour; funnel becomes deformed, winds inside of storm blow in different directions aloft and near ground, circulation forms an elongated rope shape; cold outflow air wraps around tornado

derecho

line of intense, widespread, and fast-moving windstorms and sometimes thunderstorms that moves across a great distance and is characterized by damaging winds

convective zone

line of thunderstorms just behind gust front -heavy rain, strong gusty winds -line of high reflectivity on image

How are lightning fatalities separated by gender? Geography?

more men are struck by lightning; location of strikes can be generally predicted but not exactly

Why are downdrafts important in supercell tornadogenesis?

need a downdraft to bring rotation from aloft to the ground

Do mountains, cities, lakes, or bodies of water prevent tornadoes?

no

safest places in a lightning storm

-car -house (away from corded electronics and water)

lightning safety

-don't lay on the ground -crouch down on the balls of your feet -minimize your contact with the ground

What are typical lifting mechanisms that can trigger thunderstorms?

-fronts -surface convergence -orographic lift (air forces to rise by a mountain) -sea breeze -rising of thermals of air

tornado safety

-get to the lowest floor of a substantial structure; basements preferred -don't waste time opening or closing windows -get to an interior room; put as many walls between you and the tornado as possible -stay away from windows -protect yourself from flying debris -don't wait for sirens to sound -cars, trucks, mobile homes are NOT safe

unsafe places in a lightning storm

-golf course (or anywhere outdoors) -under a tree -any place where you are the tallest object (water, mountaintop)

hail safety

-if outdoors, get indoors -if in a car, pull over to safe place and cover eyes/face if glass is breaking -do NOT block roadways/hide under overpasses to seek shelter from hail -if indoors, stay away from windows

How does hail form? What type of thunderstorm produces the largest hail?

-small ice particle suspended in updraft -supercooled water within updraft freezes to hail embryo and particle grows -a stronger updraft can suspend a heavier and thus larger hailstone -hailstone falls back to earth when it is ejected from the updraft **heavy-precipitation supercells**

What are three thunderstorm types?

1. ordinary (single-cell) 2. multicellular 3. supercell

the sequence of events of a lightning strike

1. stepped leader 2. return stroke 3. dart leader 4. second return stroke

What are the three ingredients for thunderstorm formation? What additional ingredient is needed for severe thunderstorm formation?

1. unstable atmosphere 2. lifting mechanism 3. surface moisture **vertical wind shear needed for severe thunderstorm formation**

dry adiabatic lapse

10 degrees C per km -a parcel of dry air (RH<100%) cools at this rate when it ascends and warms when it descends

moist adiabatic lapse rate

6 degrees C per km -a parcel with RH=100% cools at this rate when it ascends (only applied to ascending parcels of air)

What is the definition of a tornado?

A violent rotation column of air attached to a t-storm and in contact with the ground

Where are thunderstorms most common in the United States? Why?

Florida; because of the ideal temperature and humidity

overshooting top

Found above the anvil -Associated with a very strong updraft -top of updraft may penetrate into stratosphere

What is the typical electric charge separation inside of and near a thunderstorm?

Positive charge at the top of cloud, negative charge at base of the cloud; positive charge accumulates on tall objects because of the attraction to the negatively charged cloud base

lifting condensation level (LCL)

The altitude at which an air parcel becomes saturated -located at the intersection of the saturation mixing-ratio line that passes through the surface dewpoint temp with the dry adiabat that passes through the surface temp (toward the bottom of a skew chart-starting point) **is a kink in the line near the bottom of the graph**

hook echo

The shape of an echo on a Doppler radar screen that indicates the possible presence of a tornado

What is atmospheric instability?

a condition where the earth's atmosphere is generally considered to be unstable and as a result the weather is subjected to a high degree of variability through distance and time

What does a supercell updraft look like? The FFD? The RFD?

a cumuloform cloud; the FFD contains heavy rain-visibility is limited; the RFD appears as a clear slot near the updraft base

downdraft

a downward current or draft of air -when air is cooler than its surroundings, it sinks -precipitation is required to form

supercell

a long lived, rotating thunderstorm -most intense thunderstorms on the planet -always rotate -produce majority of tornadoes

What is a wall cloud? How does it form?

a lowered cloud base beneath the updraft; forms as a storm ingests humid, rotating air from forward-flank downdraft

When (during a year and during a day) are tornadoes most likely? Why?

april-july/august; 2-8 pm

Why do ordinary thunderstorms only last for about an hour?

because the updraft is not separating from the downdraft

what is a gust front or an outflow boundary?

boundary between cold outflow and warm inflow; this is why the temp drops and winds increase just before a thunderstorm begins

How do non-supercell tornadoes form? What are they called?

form from a vertically spinning parcel of air already occurring near the ground caused by wind shear from a warm, cold or sea breeze front, or a dryline; gustnado, landspout, waterspout

anvil

formed from air diverging outward when it reaches tropopause; flat cloud at top of a storm

trailing stratiform region

large area of light to moderate rain behind convective zone

shelf cloud:

large, low-hanging, typically non-precipitating

What is a shelf cloud? How does it form and what weather conditions might be expected as one passes?

large, low-hanging, typically non-precipitating cloud; formed by an inflow and outflow of air-does not rotate; brings gusty, cold air

equilibrium level (EL)

point where the anvil forms; marks the top of the storm -to locate: from the LFC proceed upward along a saturation adiabat (vertical curves) until it intersects the temperature profile (at the top of sounding)

What causes this charge separation?

positively charged ice crystal is light and floats to the top of the cloud; negatively charged graupel particle is heavy and falls to the bottom of the cloud

What is the typical life cycle of an ordinary thunderstorm?

rarely severe; lasts about an hour 1. towering cumulus stage (updraft) 2. mature stage (downdraft) 3. dissipating stage (downdraft)

Where in the United States are tornadoes most likely?

tornado alley and dixie alley

How does the temperature of air change as it rises and sinks? Why?

rising air cools by expansion; sinking air warms by compression **pressure and temperature decrease with height**

What is a mesocyclone? How does it form?

rotating updraft; when winds intensify, the force released can cause the updrafts to rotate

What is a bow echo and what is the main weather hazard associated with them?

section of high radar reflectivity (intense storms) that "bow" outward; MCS mesoscale convection system

microburst

smaller and more intense downburst

downburst

strong downdraft that comes in contact with the ground -sinking air is colder than the air around it -rain falls into unsaturated air and evaporates -rain drags air downward with it

why do supercells typically persist for much longer than ordinary thunderstorms

strong winds aloft in supercell environments blow precipitation out of the updrafts

level of free convection (LFC)

the level above the ground that the parcel first becomes warmer than its environment -to locate: continue up from LCL along a saturation adiabat until you intersect the sounding temperature curve

environmental lapse rate

the rate of decrease of temperature with altitude in the stationary atmosphere at a given time and location

Why is lightning from the anvil more dangerous than that from the base of a storm?

they are more unexpected and more dangerous

lifted index (LI)

tool used by meteorologist to determine the stability of the atmosphere; if the LI is NEGATIVE, then the environment is UNSTABLE formula: temp of environment at 500 mb - parcel temp at 500 mb

outflow

when the cold downdraft reaches ground, it spreads outward and forms a pool of cold air at the surface beneath a storm

What are the criteria used by the National Weather Service to determine if a storm is severe? How often does each type of severe weather occur in the US each year?

winds of 58 mph OR hailstones of 1" or greater OR tornado wind: avg 15,000 per year hail: avg 10,000 per year tornado: avg 1200 per year