Steve Jones said:I try to face the doorway away from driven rain, so that I
can leave it unzipped in the night. Doesn't always work
(not with my luck anyway) as the wind has a penchant for
turning during the night to a more unfavourable direction,
except that is, when I try the 'double bluff' routine and
park it into the wind to start with!
Here's a tip. The prevailing wind in the UK is south-
westerly. This is the direction it blows when a frontal
system is moving in. Most frontal systems pass to the north
of us. As the system crosses the wind "veers" to the north-
west, where it is at it's strongest. As the system passes
the wind then "backs" to the south-west ready for the next
frontal system (although if you're lucky you may get a lull
in the wind if there's a ridge of high pressure in between).
So as a general rule it's best to face the door of the tent
to the east. Since the wind can often shift direction by 90
degrees during the night, it will typically vary from 45
degrees behind you on one side to 45 degrees behind you on
the other.
Of course, this only works with a "typical" frontal system,
which usually arrive from the west and pass to the north of
the UK. Sometimes they can pass to the south in which case
the wind direction will change from south-east to north-east
as it passes. This is more likely to happen the further
north you are, so it may be quite common in Scotland, but
it's quite rare in Wales.
If the system crosses directly over you then the wind will
change from the south to the north with a deadly lull in
between (the eye of the storm!). This is pretty rare.
Also be aware that the complex shape of mountains can alter
local wind patterns due to wind funnelling up and around
valleys and over cols. This is very interesting and often
difficult to predict. If you know which direction the wind
is supposed to be blowing in (check the weather forecast)
look at the shape of the valleys on the map to try to figure
out how they could affect the flow of the wind. Something to
do while you're in your tent trying to figure out why my
advice didn't work... ;-)
But as a basic rule of thumb, pitch the tent facing east.
If it's raining then it's probably coming from the west. If
it's snowing then it's probably coming from the north,
which is a different matter entirely. If it's blowing from
the east it will be very cold but probably won't rain or
snow. If it's blowing from the south you may get sand
deposited on your car (from the Sahara, very rare this but
it does happen).
You know about Ballot's Law don't you? If you stand with
your back to the wind the centre of the low pressure system
is to your left. Usually this means that if your left faces
northwest then there's a pressure system moving in, if it
faces northeast then it will pass soon.
It's important to remember that the wind direction on the
ground is not the same direction that the system is moving
in. Sometimes you can see high clouds moving in a different
direction to the wind on the ground. Sometimes you can see
high and low clouds moving in different directions.
Fascinating stuff. Using Ballot's Law and watching high
clouds can give you a good idea of where the low pressure
system is and which way it's moving, helping you to predict
wind direction. Very useful if you're out for a while and
haven't heard a recent forecast.
Paul
--
wilderness-wales.co.ukwilderness-wales.co.ukOpen ↗
wildwales.fsnet.co.ukwildwales.fsnet.co.ukOpen ↗
photosig.comuserphotosOpen ↗