|
|
 |
H
is for…
Helm Wind
This is a strong, cold wind from the northeast, which blows down
the western slope of the Cross Fell mountain range in Cumbria, usually
during late winter and spring.
It causes a thick bank of cloud, known as the Helm, to sit along
the top of the fells, and a stationary roll of whirling cloud to
form at the same level 1 to 6 km to the west, known as the Helm
Bar.
It is a very localised phenomena: a gusty, violent wind as it descends
the fell sides, but which stops abruptly under the Helm Bar. It
dries the air out dramatically and is an example of Lee Waves.
Hurricane
This is the name, originally from Spain or Portugal, given to intense
tropical cyclones, or low pressure systems, which occur in the Atlantic,
Caribbean and Gulf of Mexico.
 |
| Hurricane
force winds |
They
are known as Typhoons in the Pacific, and often bring very heavy
rain as well as high winds. The energy which drives the storm comes
from high sea temperatures, and for a hurricane to thrive, the sea
over which it travels must exceed 26.5 degrees Celsius. "Hurricane
Force" winds on the Beaufort scale (see our B-section) are
force 12, which means a mean speed of 64 knots or more.
Sustained winds of this strength are very unusual in the UK, although
gusts do often reach these speeds. One notable exception, where
hurricane-strength winds were recorded, was the great storm of 15-16th
October 1987.
Gusts of over 80mph were recorded continually for over 4 hours in
many places, and the highest gust recorded was 122mph at Gorleston
in Norfolk. 18 people died and severe damage was sustained to buildings
and trees over much of southern England.
 |
| Fog
is caused by humid air |
Humidity
This is a measure of the amount of water vapour held in the air.
High humidity can make hot climates harder to cope with, as our
bodies cannot evaporate moisture off them in order to keep cool.
This isn’t usually a problem for holidaymakers in the north
of England though, where the effects of high humidity in cooler
air are more likely to be seen - as mist and fog!
High
This is a term often used to denote an anticyclonic weather system,
with high pressure at the centre, and winds which blow clockwise
around it.
 |
| Nothing
but blue sky! |
During
the summer months a semi-permanent high from the Azores often pushes
up across Britain, and can bring spells of settled, warm weather.
However this summer it hasn’t been very successful in establishing
itself for any length of time!
High pressure doesn’t always mean fine weather though - sometimes
when the high centre is in the North Sea the clockwise winds bring
cloud and even sea mists onshore down the eastern side of the country,
and so the Northeast in particular may be dull and cool.
|
