Severe/Unusual Weather Exam 2

what is relative humidity?

percent of water vapor in the air compared to what would be present if air were saturated

what is dewpoint temp?

temp that the air must be cooled to (at a constant pressure) to reach saturation

what is temperature?

average speed of molecules in a substance

what is sublimation?

change is phase directly from ice to water vapor

what is deposition?

water goes directly from a gas to solidh

what occurs if a substance going to a higher energy state?

energy is absorbed from the atmosphere

atmosphere cools

what is a jet stream?

fast moving current of air in the upper atmosphere

what causes jet stream?

unequal solar heating combined with earth’s rotation

what can jet streams do?

intensify surface systems

create difference in wind speed/direction with height (= severe weather)

steer storms

what is air parcel?

volume of air that has its own temperature characteristics separate from surrounding air

can move up/down throughout environment depending on temp of the parcel and surrounding air (won’t mix with surrounding air)

what is a dry air parcel?

air is not saturated

cools at a rate of 5.5 degrees F per 1000 feet

what is a saturated air parcel?

relative humidity is 100%

cools at rate of 3.5 degrees F per 1000 feet

what is radiosonde?

takes measurement on weather balloon

what is environmental lapse rate?

how much temp changes in environment

what is an unstable environment?

condition in which air parcels rise on their own because they are warmer and less dense than surrounding air

when in convection?

method of heat transfer within fluid (ex: water or air)

what is topography? how does it work?

orographic lifting

air is blowing from left to right towards a mountain. it hits the mountain and cannot go anywhere but up, so it rises up the mountain. as it does so, it cools to the dew point temp and clouds and precipitation can form

what is convergence?

accumulation of air in a region that forces air up

what is a front? what are the four major types?

where any two air masses meet

cold fronts, warm fronts, stationary fronts, occulded fronts, dry lines

what is the adiabatic process?

change in temp without adding or removing heat

what is a extratropical cyclone?

low pressure mid-latitude weather system characterized by converging winds and ascending air rotating counterclockwise in northern hemisphere and clockwise in southern hemisphere

forms at front between polar and ferrel cells

what is air mass?

huge body of air that has similar temp, humidity, and air pressure at any given height

how are air masses classified by latitude?

(T) tropical = warm-hot

(P) polar = cold-cool

(A) arctic = extremely cold

what are moisture characteristics of an air mass?

maritime (m) used for air masses originating over water

continental © used for air masses originating over land

what is a cold front?

transition zone where cold air mass is replacing warmer air mass

generally move from NW to SE

dry air, comma shape, shift in winds, can cause storms, low dew point temps

what are warm fronts?

transition zone where warm air replacing cool air

what is a stationary front?

can result when either cold or warm front stops moving

winds can blow parallel

storms can occur

what is an occluded front?

fast moving cold front overtakes a slower warm front, lifiting warm air mass of the ground

what is a dry line?

boundary the separates a moist air mass originating in gulf of mexico from dry air mass originating in desert SW

dew point front because of sharp changes in dew point

what is a polar front?

boundary separating polar air masses in north from warmer air masses in south

often stationary, so winds may be blowing parallel to front

what is a blizzard?

strong winds blowing snow that results in low visibilities

sustained winds or frequent gusts that are greater/equal to 35 mph for prolonged period of time (~ 3 hours)

what are the two types of blizzards?

alberta clippers

colorado lows

what is an alberta clipper blizzard?

typically colder temperatures

what is a colorado low blizzard?

typically more snow

when is an ice storm warning issued?

accumulation of ice expected to be ¼ inch or more

when is a winter weather advisory issued?

hazardous winter weather in expected, but conditions should not be severe enough to reach warning criteria

when is a wind chill advisory issued?

wind chill temps expected to be significant inconvenience to life with prolonged exposure

if caution not exercised, could lead to hazardous exposure

criteria for issuing is set locally

what is the wind chill factor?

describes what happens to a body when its cold and windy

what is hypothermia?

body temp passes below 95 F

what is sleet?

pellets of ice that start as snow, warm for a little bit then cold

what is freezing rain?

comes down as a liquid but freezes on contact with a cold surface

starts as snow in warm then very shortly in cold

what is rain?

starts as snow (atmosphere) warms in air

an unstable air mass is a mass of air which, if pushed up, will tend to…

remain warmer than surrounding air and rise

a saturated parcel of air that is lifted will expand and cool at the ____?

moist adiabatic lapse rate

a stable air mass is a mass of air which, if pushed up, will tend to ____?

remain cooler than surrounding air and sink

clouds are most likely to form when ____?

air rises due to heating of the earth’s surface

during which phase change is latent heat absorbed from the atmosphere?

evaporation and sublimation

what is latent heat?

energy associated with phase changes

what is the dry adiabatic lapse?

rate of cooling or warming that takes place in a rising or descending parcel of unsaturated air

this phase change occurs when water vapor in atmopsphere turns directly to ice

deposition

a column of air that is only experiencing convergence will ____?

have a higher mass and increased surface pressure

an approaching extratropical cyclone would be identified by a ____ barometer reading?

falling

what direction does a cold front move early in its lifetime?

south

how are extratropical cyclones beneficial?

bring rain to agricultural producing regions of US

what are high pressure centers associated with?

divergence at surface and convergence aloft

if convergence in the upper atmosphere exceeds surface divergence, what happens to the air molecules

more added to surface than are removed = surface pressure increases

Iowa City is under influence of continental tropical airmass. if maritime tropical airmass is moved over Iowa City, what happens to the dewpoint temp?

increases

what is most likely to occur when a mass of warm air moved into a region occupied by colder air?

warm front forms

warm air forced upward

how does cold air over the great plains contribute to blizzard conditions?

causes large pressure gradient to form, creating strong winds

why do colorado lows have more snow than alberta clippers?

close proximity to moisture source region

The ASOS at the local Airport is reporting wind speed of 35 mph, snow, and visibility of 3/4 of a mile; the National Weather Service forecasts that these conditions will last for most of the day. Based on this information, would the National Weather Service also issue a blizzard warning?

no, conditions are not right

→ need ¼ mile visibility or less