Fronts Flashcards
What is a front
Two air masses of different temperature and humidity meet
+++ signed along the front means
Weakening
. . . Along front means
Increasing or developing
Frontogenesis means
Formation of front
Frontocysis means
Decay of a front
Quasi Stationary Front
Not much movement (5kts)
Little interaction so no sig weather
Wind flows from cold to warm and is deflected 90 degrees to blows along frontal zone
Cold front
Cold air replace warm air at surface
Unstable CB/TCU/CU
Precipitation zone 150km/300km wide
Slope 1:80
Cold front slope
1:80
How far does cloud extend in cold front
50-100nm
Clouds when approaching cold front
CB/TCU/CU
Temperature and pressure at cold front
Temp decreases
Pressure is lowest at the front
Pressure increases after front
Warm front is
Warm air replacing cold at at surface
Stable CI/CS/AS/NS
1:150 slope
Continuous and moderate rain
What happens to pressure/temp at warm front
Temp increase
Pressure decreases
Humidity increases
How fast does a warm front move
10-15kts
How fast does a cold front move
20-20kts
Pressure at warm/cold front
Isobars bend at fronts
Warm front pressure decreases
Cold front passes pressure increases
Mediterranean front
Only occurs in winter
Cold air moving down from continental Europe
Warm air moving up through North Africa
Polar air meets tropical air
The Artic Front
Only occurs in winter
Division between maritime artic and maritime polar
Polar fronts
Meeting of polar air and sub tropical air
Summer warm air mass in line past UK and NE Canada
In winter cold air moves south across Atlantic (Florida to uk)
Polar front depression formation
Occurs at a stationery front
Warm air backs into cold air and cold air back into cold
Causes warm air to rise causing a pressure gradient
More air drawn into cold air to strength the low level winds
Deflection via Coriolis anticlockwise to form a low pressure system
Polar front stages
Stationary front
Frontal wave
Open wave
Mature (initial occlusion)
Advanced inclusion
Cut off cyclone
Warm front - clouds/precipitation/slope/temp/pressure/humidity
Warm air slide over colder air
Frontal slope is shallow around 1:150
Rises slowly and cools adiabatically
Stratiform clouds
Cirrus clouds - cloud base lowers altostratus/nimbostratus/stratus - clouds can extend 500 miles ahead
Freezing rain/drizzle - precipitation zone 350km ahead
Temp goes up
Pressure decreases
Humidity goes up
Moves at 10-15kts
Where are the strongest winds in a polar front depression
Occurs between polar air tropopause about 300-400nm ahead of warm front
Warm front speed
Speed of about 10-15kt 2/3rd of Geostrophic wind speed
Warm front winds
Backs initially then veers at the front with steady increase in speed
South Westerly to Westerly at the warm sector
Warm sector - source/clouds/precipitation/temp/pressure/humidity
Temperature increases
Pressure decreases
Relative humidity decreases
Winter can bring stratus
Summer - clear skies and fair weather cumulus/haze sometimes
Stable tropical maritime air
Light precipitation
Cold front - precipitation/clouds/slope/temp/pressure
Cold dense air slides underneath warmer tropical maritime air
Cools adiabatically/ELR increases rapidly/instability
Intense line of CB clouds the entire length of cold front
Thunderstorms just head of surface position of front
Heavily embedded cbs in NS/AS
Intense precipitation/heavy snowfall in winter
Slope is 1:80
Weather band is 30-50nm wide
Temp decreases
Pressure lowest at front then increases
Humidity increases
Passage of wind along polar front depression
Moves from south westerly before warm front
Moves westerly at warm sector
Moves north westerly at cold sector
Warm Occlusion
Cold air catches up to displace warm sector but coldest air at the front - Common in the winter
Cross Section would show cold air at back rising above more dense colder air at front with warm sector in the middle off the ground.
Embedded CBS ahead of occlusion
Cirrus/AS/Snow/rain/stratus at warm front
Towards back embedded CB/NS/AS
Cold Occlusion
Coldest air at the back of front - common in summer
Cross section: Colder more dense air at rear of front would cause rear polar maritime air to undercut the warmer air at front. Warm sector will be hovering off the ground above.
Precipitation falls on both side
Embedded CBS
Approximate latitudes of polar front in NH in summer and winter
Summer 60N
Winter - 50N
Precipitation zone ahead of warn front
200nm
During the passage of a cold front what wind conditions can you expect
Westerly winds becoming north westerly and increasing
Polar Low
Small intense maritime cyclone that form in cold polar air that moves over warmer water
100-500km and last between 12/36 hours
What has the highest likelihood of encountering thunderstorms/CBS and convective clouds.
Slow moving cold front
Most mid latitude depressions move from west to east in both hemispheres
Where is the worst weather in an occluded front
Near the apex of the occlusion
Weather development on approach to a warm front
800km ahead of surface overcast cirrostratus
Cloud base lowers to become overcast altostratus
Nimbostratus next
Around 300km ahead of surface the ac encounters rain which intensifies
Typical lifespan of a mid latitude depression
4 to 7 days
Cold front speed
20-25 knots
How long does a cold air pool last
Typical 3 days
