Occluded fronts
Cold fronts generally move faster than warm
fronts so eventually the cold front will catch up with the
warm front (or occlusion). An occluded front may be
described as "warm" or "cold" depending
on the change of temperature as it passes, but both types
generally produce cloud getting lower, then rain breaking up
into showers.
Anticyclones ("Highs")
Anticyclones, or areas of high pressure, are
much less active than depressions.
Their isobars are usually more widely spaced
than those of a depression, so winds are generally light and
the weather is generally fine, though in winter the sky may
be overcast.
Once an anticyclone becomes established its
movement is likely to be slow and irregular, and it may
remain stationary for days or weeks on end.
The atmospheric stability associated with a
high is likely to promote coastal fog in spring and autumn.
In summer, trapped dust particles may form haze.
Weather around depressions
The fronts associated with a typical
depression divide the area around it into distinct sectors,
each with distinctive weather patterns.
| Wind |
increases and backs (e.g. SW to S) as
the front approaches, then veers (e.g. from SW to W)
as the front passes |
| Cloud |
cloud cover increases and cloud base
lowers as the front approaches |
| Weather |
rain, becoming heavier and continuous |
| Visibility |
reducing as the front approaches |
| Pressure |
falling as the front approaches |
| |
The warm sector
|
| (between the fronts, generally S or
SE of the depression's centre) |
| Wind |
steady |
| Cloud |
low cloud, almost 100% cover |
| Weather |
steady drizzle or light rain |
| Visibility |
moderate or poor, possibly foggy |
| Pressure |
steady |
| Wind |
may increase and possibly back (e.g.from
W to SW) as the front approaches then veers (e.g.
from W to NW) as the front passes |
| Cloud |
dense cloud, possibly towering to
great heights at the front itself, quickly breaking
up into to smaller puffy clouds once the front has
passed |
| Weather |
heavy rain, followed by showers once
the front has passed |
| Visibility |
poor in rain, then good or very good |
| Pressure |
rises as the front passes |
| Wind |
may veer a little and freshen or
become gusty immediately behind the cold front (depending
on the depth and movement of the depression) |
| Cloud |
apart from any frontal cloud nearby
generally clear skies with scattered showers or
white 'fair weather cumulus' |
| Weather |
fair |
| Visibility |
generally good |
| Pressure |
depends on the depth and movement of
the depression, but generally rises quickly as the
cold front passes, then more slowly |
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