Download File - Year 9 Outdoor Education

WEATHER
Winter Alpine weather can be extremely
variable.
Weather is caused by large atmospheric
motions organised into bands of high and
low pressure. During winter, southern parts
of Australia come under the influence of
lows and their associated cold fronts,
exposing it to cold maritime air. This leads
to frequent rain which falls as snow on
higher ranges.
Insert an image for High & Low pressure
systems on the right.
In high pressure systems,
____________________________________
____________________________________
In low pressure systems,
____________________________________
____________________________________
When a low and a high pressure system replace each other a mixing takes place known as
a front which brings with it a change in temperature, pressure, wind strength and wind
direction. A cold front occurs when cold air replaces warmer air; the cold air undercuts
the warm air pushing it upwards and causing large clouds to develop.
Cold fronts are associated with lows moving from the west coast to the east coast of
Australia. Diagram A illustrates a typical snow producing weather pattern. A cold front
is preceded by thin wispy cirrus clouds at high altitude. These thicken and are replaced
by lower cloud as the front begins to move in. The front brings with it rain or snow which
will be wet snow if there is warmer air ahead of the front and this turns to colder drier
snow as the front passes.
With high pressure systems over central Australia, mountains experience almost
continuous westerly winds with fronts passing every few days.
Southerly Outbreaks occur when strong high pressure systems sit in the great Australian
Bight with deep low pressure systems south of Tasmania. Cold air is drawn up from the
south very quickly. Southerlies occur only a couple of times during the winter but brings
bitterly cold conditions and huge dumps of snow.
What do isolated fluffy clouds suggest to a skier? ________________________________
What does the saying “Red Sky At Night” imply?
_______________________________________________________________________
SNOW AND WIND
Different types of snow conditions in different areas require different ski techniques to be
successful.
Icy conditions require: _____________________________________________________
Where as powder snow lends itself to: _______________________________________
In spring, the night air temperature falls below freezing therefore the snow freezes at night
into little ice granules. By the afternoon in 22 degree temperatures the snow tends to get
heavy and slush.
Moguls result from:
Wind chill factor
A severe wind in –20 degree temperatures
can lead to a skier being prone to extreme
hypothermia. Wind chill factor needs to be
considered at all times by touring skiers. The
chill factor is particularly pronounced at
lower temperatures. Determine what the chill
effect would be if :
a) thermometer reading of 0 degrees and a
60km/h wind
_________________________
b) thermometer reading of –20 degrees and
a 30km/h wind
________________________
c) thermometer reading of –20 degrees and
a 60km/h wind
_______________________