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MET Key Facts > Fronts > Flashcards

Fronts Flashcards

1
Q

What is a front

A

Two air masses of different temperature and humidity meet

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2
Q

+++ signed along the front means

A

Weakening

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3
Q

. . . Along front means

A

Increasing or developing

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4
Q

Frontogenesis means

A

Formation of front

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5
Q

Frontocysis means

A

Decay of a front

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6
Q

Quasi Stationary Front

A

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

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7
Q

Cold front

A

Cold air replace warm air at surface

Unstable CB/TCU/CU

Precipitation zone 150km/300km wide

Slope 1:80

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8
Q

Cold front slope

A

1:80

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9
Q

How far does cloud extend in cold front

A

50-100nm

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10
Q

Clouds when approaching cold front

A

CB/TCU/CU

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11
Q

Temperature and pressure at cold front

A

Temp decreases
Pressure is lowest at the front
Pressure increases after front

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12
Q

Warm front is

A

Warm air replacing cold at at surface
Stable CI/CS/AS/NS
1:150 slope
Continuous and moderate rain

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13
Q

What happens to pressure/temp at warm front

A

Temp increase
Pressure decreases
Humidity increases

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14
Q

How fast does a warm front move

A

10-15kts

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15
Q

How fast does a cold front move

A

20-20kts

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16
Q

Pressure at warm/cold front

A

Isobars bend at fronts
Warm front pressure decreases
Cold front passes pressure increases

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17
Q

Mediterranean front

A

Only occurs in winter
Cold air moving down from continental Europe
Warm air moving up through North Africa

Polar air meets tropical air

18
Q

The Artic Front

A

Only occurs in winter

Division between maritime artic and maritime polar

19
Q

Polar fronts

A

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)

20
Q

Polar front depression formation

A

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

21
Q

Polar front stages

A

Stationary front
Frontal wave
Open wave
Mature (initial occlusion)
Advanced inclusion
Cut off cyclone

22
Q

Warm front - clouds/precipitation/slope/temp/pressure/humidity

A

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

23
Q

Where are the strongest winds in a polar front depression

A

Occurs between polar air tropopause about 300-400nm ahead of warm front

24
Q

Warm front speed

A

Speed of about 10-15kt 2/3rd of Geostrophic wind speed

25
Q

Warm front winds

A

Backs initially then veers at the front with steady increase in speed

South Westerly to Westerly at the warm sector

26
Q

Warm sector - source/clouds/precipitation/temp/pressure/humidity

A

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

27
Q

Cold front - precipitation/clouds/slope/temp/pressure

A

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

28
Q

Passage of wind along polar front depression

A

Moves from south westerly before warm front
Moves westerly at warm sector
Moves north westerly at cold sector

29
Q

Warm Occlusion

A

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

30
Q

Cold Occlusion

A

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

31
Q

Approximate latitudes of polar front in NH in summer and winter

A

Summer 60N
Winter - 50N

32
Q

Precipitation zone ahead of warn front

A

200nm

33
Q

During the passage of a cold front what wind conditions can you expect

A

Westerly winds becoming north westerly and increasing

34
Q

Polar Low

A

Small intense maritime cyclone that form in cold polar air that moves over warmer water

100-500km and last between 12/36 hours

35
Q

What has the highest likelihood of encountering thunderstorms/CBS and convective clouds.

A

Slow moving cold front

36
Q

Most mid latitude depressions move from west to east in both hemispheres

A
37
Q

Where is the worst weather in an occluded front

A

Near the apex of the occlusion

38
Q

Weather development on approach to a warm front

A

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

39
Q

Typical lifespan of a mid latitude depression

A

4 to 7 days

40
Q

Cold front speed

A

20-25 knots

41
Q

How long does a cold air pool last

A

Typical 3 days

MET Key Facts (25 decks)

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