Fronts and frontal depressions Flashcards
What separates two air masses of different temperature / density
Weather front
How wide can a front be?
Up to a few kilometres wide. Often described as a zone where the change is gradual.
There are 3 main global frontal systems
Polar front
Artic front
Equatorial Trough / ITCZ
(also Mediterranean front in Europe)
Warm front:
Describes which part of the front
Leading edge
Warm front:
How does it move in relation to the retreating cold front?
Rises over and replaces
Warm front:
Have a greater effect on the weather in (spring/summer/autumn/winter)?
Winter
Warm front:
What is the expected angle of the front. It slopes upwards at a gradient of
1:150
Warm front:
Conditions as surface front approaches:
Clouds?
High clouds, progressively lowering as the surface front nears.
Ci - Cirrus
Cs - Cirrostratus
As - Altostratus
Ns / St - Nimbostratus / Stratus
Warm front:
Conditions as surface front approaches:
Weather?
Steadily worsening to intermittent/continuous rain/drizzle/snow at the front.
Warm front:
Conditions as surface front approaches:
Pressure?
Steadily falls as the warm front approaches
Warm front:
Conditions as surface front approaches:
Wind?
Backs - the veers as the front passes
Warm front:
Conditions as surface front approaches:
Aviation hazards
Potential FZRA/FZDZ
moderate rime icing
low cloud
poor visibility
possible mist / fog
Cold front:
Have a greater effect on the weather in (spring/summer/autumn/winter)?
Winter
Cold front:
Slope forwards/backwards and at what gradient?
Any exceptions
Generally backwards
1:75
Small forward sloping section at the surface
Cold front:
Conditions at a cold front:
Cloud - Initially, then and after?
Nimbostratus [Ns] and Stratus [St] with embedded Cumulus [Cu] / Cumulonimbus [Cb]
Then
(mid level 6500ft +)
Altostratus [As] Altocumulus [Ac]
(High level 20,000ft+)
Cirrostratus [Cs] Cirrocumulus [Cc]
Then well behind the front:
Cirrus [Ci]
Cold front:
Conditions at a cold front:
Weather?
Heavy intermittent or continuous rain with showers at or just ahead, decreasing further behind the front.
Cold front:
Conditions at a cold front:
Ground visibility?
Poor during precipitation, improving further behind
Cold front:
Conditions at a cold front:
Pressure?
Slight decrease on approach, increases after the passage of the front
Cold front:
Conditions at a cold front:
Aviation hazards:
CBs
heavy showers of Rain [RA]
Possible:
Hail [GR] or small hail [GR]
Clear icing
Wind gusts/wing shear
Lightening
Warm sector:
What type of air mass is typical?
Where does this live in relation to fronts?
Tropical maritime
Between warm and cold fronts
Warm sector:
Properties - Cloud?
Stratus (St)
Stratocumulus (Sc)
Fog / mist
Warm sector:
Properties - Weather?
Light drizzle
Warm sector:
Properties - Ground visibility?
Moderate, poor in low cloud, drizzle mist and fog or good in the summer with fair weather Cumulus (Cu)
Warm sector:
Properties - Pressure and wind?
Constant
Wind constant, from West or South-West
Warm sector:
Properties - seasonal effects?
Winter fronts usually produce more weather and lower clouds
Occluded front:
Formed by?
Cyclogenesis, when a cold front catches up and then
Overtakes a warm front.
Occluded front:
What word is synonymous with ‘occluded’ and how does this relate?
The air in the warm sector is separated (occluded) from the surface.
Occluded front:
Shares characteristics from…
The weather has the characteristics of both warm and cold fronts.
Occluded front:
The sequence of clouds ahead of the occlusion is similar to the sequence of
clouds ahead of a____ _____
warm front.
Occluded front:
The cold front weather occurs near the _____ _____ _____
upper cold front.
Occluded front:
The worst weather is near the ____ __ ___ _________
apex (tip) of the occlusion.
In Europe warm Occlusions are more common in ______ ….
winter; cold occlusions in summer.
How can the precipitation area be described near a quasi-stationary front?
A wide area on the cold-air side and sometimes patchy along the line of the front itself.
Most mid-latitude depressions move from ____ to ____ in both hemispheres, powered and pushed by the prevailing westerlies and jet-streams.
Most mid-latitude depressions move from west to east in both hemispheres, powered and pushed by the prevailing westerlies and jet-streams.
The whole polar front moves In the direction, and parallel to the isobars in the warm sector at a speed determined by the
geostrophic interval of the warm sector isobars.
An individual front moves approximately _____________ to the front or more or less __ ____ with the isobars behind the front.
An individual front moves approximately perpendicular to the front or more or less in
Line with the isobars behind the front.
The speed of the front is calculated by using?
The geostrophic interval along the front itself.
Do warm or cold fronts move faster?
Generally cold fronts move faster than warm fronts.
Cold fronts move approximately equal to the ___________ _______
Cold fronts move approximately equal to the geostrophic interval.
Warm fronts move at approximately 70% of ___ ____________ ________
Warm fronts move at approximately 70% of the geostrophic interval.
A polar front depression moves in the direction, and parallel to,
the isobars in the warm Sector at a speed determined by the geostrophic interval of the warm sector isobars.
The stages and life cycle of a mid-latitude depression are
Cyclogenesis
Mature,
Occluded
Frontolysis,
Westerly waves; The west to east passage of waves of weather associated with
polar Front depressions or mid-latitude lows,
Mountains can strengthen or weaken fronts, accelerate or decelerate fronts and
make fronts harder or easier to analyse and predict.
What can this depend on?
- Depends on the orientation of the front and mountain axis.
- Channelling, blocking and other terrain induced flows modify the front.
On surface weather charts, use the ______ to assess the direction relative to ____ _____. Make corrections for land and sea tracks, and calculate the wind speed using the ______ _______ and the ____________ wind scale.
On surface weather charts, use the isobars to assess the direction relative to true
north. Make corrections for land and sea tracks, and calculate the wind speed using
the isobar spacing and the geostrophic wind scale.
Atmospheric divergence / convergence
Sinking (high pressure) tends to be more gentle so pressure gradients are less; isobars are further
apart and wind is slower.
Rising (low pressure) The ascent can be strong so pressure gradients can be greater, isobars closer and wind will be faster.
