Download Weather - Broxbourne School

BROXBOURNE SCHOOL
YEAR 12
EXPEDITION TRAINING
The weather controls an expedition
more than anything else, it is the one thing
that we cannot change.
It is vital that we know what to expect in wild country.
Mountain weather conditions can change dramatically from one
hour to the next.
A morning that dawns clear and sunny can turn into an afternoon
plagued by thunderstorms and gale force winds.
In fact, gale force winds can be blasting the top
of a mountain while the valleys below are calm.
As a result, anyone planning to venture into a mountainous region,
whether hill walking in the Peak District,
or mountain climbing in the Andes or Himalayas,
needs to know what type of weather to expect.
It is vital that they check the forecast
before they leave and, while in the mountains,
that they pay constant attention to any changes in the weather.
Basic forecasts can be obtained from the TV, radio,
and newspapers., but these are very general for mountain areas.
There are websites that you can visit for a more detailed
Forecast for a mountain area.
www.ukclimbing.com
www.met-office.gov.uk
Or you can phone;
Met Office 09068 500 449 - Snowdonia
Wind is simply air in motion, moving from
high pressure to low pressure.
Winds are described by the direction they blow from –
an easterly wind lows from the east, a westerly from the west.
Beaufort
number
Wind speed
kt
km
/h
mp
h
m/s
Description
Land conditions
0
0
0
0
0-0.2
Calm
Calm. Smoke rises vertically.
1
1-3
1-6
1-3
0.3-1.5
Light air
Wind motion visible in smoke.
2
4-6
711
4-7
1.6-3.3
Light breeze
Wind felt on exposed skin. Leaves rustle.
3
710
1219
812
3.4-5.4
Gentle
breeze
Leaves and smaller twigs in constant motion.
4
1116
2029
1318
5.5-7.9
Moderate
breeze
Dust and loose paper raised. Small branches begin to move.
5
1721
3039
1924
8.0-10.7
Fresh breeze
Smaller trees sway.
6
2227
4050
2531
10.813.8
Strong
breeze
Large branches in motion. Whistling heard in overhead wires.
Umbrella use becomes difficult.
7
2833
5162
3238
13.917.1
Near gale
Whole trees in motion. Effort needed to walk against the wind.
8
3440
6375
3946
17.220.7
Gale
Twigs broken from trees. Cars veer on road.
9
4147
7687
4754
20.824.4
Strong gale
Light structure damage.
10
4855
88102
5563
24.528.4
Storm
Trees uprooted. Considerable structural damage.
11
5663
103
117
6472
28.532.6
Violent
storm
Widespread structural damage.
12
>63
>11
7
>7
2
>32.7
Hurricane
Clouds
Clouds form when rising air cools to a point
where it can no longer hold its water vapour.
The vapour condenses in the form of tiny droplets.
Air is lifted because of:
Widespread ascent i.e. up a warm/cold front
Encountering barriers - mountains and hills
Convection - when air is heated at low
levels by contact with sun warmed ground –
creating rising bubbles of air i.e. thermals.
.
How do we Describe Clouds?
Clouds can be cirrus (wispy), cumulus (heaped) and stratus (in layers).
They are classified into 10 main cloud types according to height and
shape.
Not all clouds bring rain, some are signs of fine weather.
The word ‘nimbus' added to the beginning or end of a cloud type,
e.g. cumulonimbus or nimbostratus,
means that the cloud is a rain cloud and will usually appear to be dark
grey.
Generally cumulonimbus are the most dangerous clouds
associated with hail, lightning, tornadoes, downdraughts, downbursts
and flashflooding.
The first kind of cloud is a cirrus cloud. Cirrus clouds are thin and wispy,
and are found very high in the sky.
Cirrus clouds point in the direction the wind is blowing. No precipitation
falls from cirrus clouds. They are a sign of fair weather for now
and the very near future.
Next are the altocumulus clouds. These clouds are like fuzzy bubbles
in long rows or strings. If you see altocumulus clouds, it usually
means that a cold front is coming. If it's summertime and
warm and humid, altocumulus clouds may turn into thunderstorms
when the cold front approaches.
After that are the nimbostratus clouds. These clouds are
dark and low-hanging clouds that cover the whole sky.
They bring with them light to moderate precipitation.
Then there are fair weather cumulus clouds. These clouds look like
big cotton balls in the sky. They have very large spaces of clear sky
in between them. Normally they don't carry any rain, but during the
spring and summer they can change into cumulonimbus clouds
Cumulonimbus clouds are thunderstorm clouds. They are tall and wide
clouds that have heavy rain, thunder and lightning.
If you see these clouds on the horizon, it is likely it will rain very soon.