TEMP RAIN
PRESSURE
LOW SUMMER
LOW WINTER
HIGH SUMMER
HIGH WINTER
Depressions
AN AREA OF LOW PRESSURE
AIR WILL RISE
COOLCONDENSE
CLOUDS
COOLSCONDENSES
CLOUDS
RAINRAIN
Air Masses An air mass can be described as 'the air with similar properties of temperature and moisture which covers a large area'.
The weather of the British Isles and surrounding countries is influenced by air masses.
Air masses formed over :-
a warm land are called Tropical Continental - Tc a warm sea are called Tropical Maritime - Tm a cold land are called Polar Continental - Pc a cold sea are called Polar or Arctic Maritime - Pm or Am
When air masses meet, fronts are formed.
What is a front?
Daily variations in the weather are caused by the influence of different air masses.
The front is the point where these different air masses meet.
Fronts can either be Warm, Cold, or Occluded.
WEATHER ASSOCIATED WITH THE PASSAGE OF A
DEPRESSION
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WEATHER ASSOCIATED WITH THE PASSAGE OF A CLASSIC DEPRESSION
Ahead of the warm frontPassage of the warm front
Warm sectorPassage of the cold front
Cold sector
Pressure starts to fall steadily continues to fall steadies starts to rise continues to rise
Temperature quite cold, starts to rise continues to rise quite mild sudden drop remains cold
Cloud cover cloud base drops and thickens (cirrus and altostratus)
cloud base is low and thick (nimbostratus)
cloud may thin and break clouds thicken (sometimes with large cumulonimbus)
clouds thin with some cumulus
Wind speed and direction
speeds increase and direction backs
veers and becomes blustery with strong gusts
remain steady, backs slightly
speeds increase, sometimes to gale force, sharp veer
winds are squally
Precipitation none at first, rain closer to front, sometimes snow on leading edge
continues, and sometimes heavy rainfall
rain turns to drizzle or stops heavy rain, sometimes with hail, thunder or sleet
showers