Meteorology Final

air mass

large body of air that has similar horizontal temperature and moisture characteristics , often originating from a specific region or source.

front

transition zone between two distinct air masses that marks a change in weather conditions such as temperature and humidity.

frontogenesis

formation, strengthening, or regeneration of a front as a result of differential temperature and pressure changes.

frontolysis

weakening or dissipation of a frontdue to a decrease in temperature and pressure differences between the air masses.

how air masses are classified

according to temperature and humiditycharacteristics, such as maritime or continental, tropical or polar.

P

air masses that originate in polar latitudes

T

air masses that originate in warm tropical regions

c

air masses that originate over land

m

air masses that originate over water

polar (P) and arctic (A)

air masses responsible for cold winters in North America

maritime tropical (mT)

air masses along east of North America, bringing hot and muggy weather

continental tropical (cT)

air masses in southwestern US that bring heat waves

stationary front

weather along front is clear or partly cloudy with colder air on Eastern side and warmer air on the Western side, often leading to prolonged precipitation

stationary

front represented by blue triangles and red semicircles on a map

stationary

front whose slope is generally shallow

cold front

cold, dry air replaces warm, moist airand is associated with thunderstorms and a sudden drop in temperature.

cold

front associated with solid blue line and triangles on a map

cold and occluded

front associated with a generally steep slope

occluded front

cold front overtakes warm frontcreating a complex weather system often leading to precipitation.

occluded

front associated with purple line on map

dryline

narrow boundary with steep horizontal change in moisture; separate moist and dry air, and often leads to thunderstorms

lake effect snow

localized snowstorms that form on the downwind side of a lakedue to cold air passing over warmer lake waters, resulting in heavy snowfall.

divergence

atmospheric condition when wind causes horizontal net outflow of air from a specific region

convergence

atmospheric condition that exists when wind causes horizontal net inflow of air into specific region

cyclogenesis

development or strengthening of a mid-latitude (extratropical) cyclone

baroclinic

instability arising from meridional (N to S) temperature gradient, strong vertical wind speed, temperature advection; mid-latitude cyclones can develop

barotropic

condition in the atmosphere where surfaces of constant density parallel surfaces of constant pressure

jet streak

region of high wind speed that moves through axis of jet stream

bomb cyclone

rapidly intensifying storm characterized by significant drop in atmospheric pressure

vorticity

measure of the spin of a fluid

polar front theory

mid-latitude extratropical cyclones form on boundaries between warm and cold air

vertical structure of low pressures

rising air and convergence leads to cloud formation and precipitation

cyclones usual formation location

Gulf of Mexico, Atlantic (east of the Carolinas), eastern slopes of Rockies and Sierra Nevadas and Cape Hatteras (NC)

cyclones usual decay location

over land OR transition to extratropical cyclone in midlatitudes

zonal flow

air circulation going E to W or W to E along latitude lines

meridional flow

air circulation going N to S or S to N along latitude lines

planetary/long (Rossby) waves

small amplitude, long wavelength; prominent wave numbers are 1-4

watch

forecast indicating conditions are favorable over a particular region during a specific period

warning

forecast indicating conditions are imminent or occurring in an area

forecast accuracy

how close a forecast is to reality

forecast skill

measure of accuracy

ensemble forecast

technique that entails running several forecast models, each beginning with slightly different weather information

forecast funnel

sequence of steps used by forecasters to analyze current and projected conditions, moving from large to small scales during the process

inches of mercury (inHg) or millibars (mb)

barometer units

1013.25mb or 14.7 pounds per sq in (psi)

typical surface pressure

short-range forecast

12-72 hours

medium-range forecast

3-8 days

long-range forecast

greater than 8 days

standardized time for weather measurement

universal coordinated time (UTC)

radiosones

launched twice a day (0000 UTC (8pm EST) and 1200 UTC (8am EST))

percent chance of rain

number is chance of rain at any point in the area during specified time

nowcasting

predicting current state or very near future of a variable using real-time data

ordinary cell (air mass) thunderstorms

form in a region with limited vertical wind shear (from growth to dissipation is about an hour)

40,000

number of thunderstorms per day

multicell thunderstorm

forms in a region of moderate to strong vertical wind speed shear; contains cells, each in a different stage of development; overall storm can last for several hours

supercell thunderstorms

form in a region of strong vertical wind shear; rotating motion often leads to tornadoes; internal structure can hold storm for hours

causes of thunderstorms

moisture, unstable atmosphere, lifting mechanism

unstable atmosphere

warm, moist surface air is lighter than cooler air above

gust front

boundary that separates a cold downdraft from warm, humid surface air

microburst

strong localized downdraft less than 4km wide that’s beneath thunderstorms

squall line

line of thunderstorms that form along a cold front or out ahead of it

derecho

strong, straight-line winds associated with a cluster of thunderstorms during night

rule for estimating distance of lightning flash

count seconds between thunder and divide by 5

the tropics

warm year round, high humidity, winds from east, located at 30 N and 30 S latitude

ITCZ (intertropical convergence zone)

low-pressure area near equator where trade winds converge, leading to abundant precipitation and band of clouds

trade winds

persistent, near-surface winds that blow towards equator from subtropical, high-pressure zones between 30-40 N and S latitude

subtropical highs

semi-permanent, high-pressure systems that exist over oceans between 20 and 40 latitude in both hemispheres

warm core

warmest temperature located at the center, with colder surrounding

cold core

coldest temperature at the center, with warmer surrounding

Enhanced Fujita Scale

describes tornado intensity by observing damage caused; based on estimated wind speeds and related structural and vegetation damage

Saffir Simpson Scale

1-5 rating system that categorizes hurricanes based on sustained wind speed

major hurricane

hurricane greater than or equal to Category 3 on Saffir Simpson Scale

super typhoon

typhoon with sustained winds of at least 150mph (240 km/h)

tornadoes

occur most often in spring

tornadoes

occur most often in central and East United States

tropical storms

occur most often in late summer and early fall

tropical storms

occur most often in NW Pacific Ocean and NW Atlantic Ocean

80

% of weak tornadoes

hook echo

radar signature for detection of possible tornado

tropical storm

low-pressure area with wind speeds between 39-73 mph

tropical depression

low-pressure area with wind speeds less than 39 mph

when tropical cyclones are named

when tropical storm intensity is reached (39mph wind or more)

storm surge, heavy rain, high wind

hazards associated with tropical cyclones