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could arise from a warm, moist air
mass flowing over cold ground.
Hill fog is low cloud covering high
ground, which may or may not have
contributed to its formation.
Frontal fog may be low cloud over
high ground, or come from rain
through unsaturated air beneath.
In shallow fog, you may be able to see
the whole of the approach and/or
runway lights from a considerable
distance, even though reports from
the aerodrome indicate fog. On
descending into the fog layer, your
visual reference is likely to drop
rapidly, in extreme cases from the
full length of the runway and
approach lights to a very small
segment. This may give the
impression of pitching nose up,
making you more likely to hit the
ground after corrective movements.
Be prepared for a missed approach
whenever you have the slightest
doubt about forward visibility. The
minimum RVR for landing from a
visual circuit is 1200m.
Mist
Essentially, thin fog, and the same
definition applies, except that the
visibility is over 1,000m.
Whiteout
Defined by the American
Meteorological Society as:
“An atmospheric optical phenomenon of
the polar regions in which the observer
appears to be engulfed in a uniformly
white glow”.
That is, you can only see dark nearby
objects – no shadows, horizon or
clouds, and you lose depth
perception. It occurs over unbroken
snow cover beneath a uniformly
overcast sky, when the light from
both is about the same. Blowing
snow doesn’t help. It’s particularly a
problem if the ground is rising. Once
you suspect whiteout, immediately
climb or level off towards an area
where you can see things properly.
Three common causes are:
· Water Fog. Thin clouds of
supercooled water droplets
contacting a cold snow surface.
· Blowing Snow. Winds over 20 kts
picking up fine snow from the
surface, diffusing sunlight.
· Precipitation. Small wind-driven
snow crystals from low clouds
having the sun shining above
them. Light is refracted and
objects obscured.
Met Services
There are many facilities to help you,
available over the Internet, by
telephone, fax or radio (our website,
www.electrocution.com/aviation.
htm has useful links). Mostly,
104 Canadian Private Pilot Studies
though, you will be dealing with your
local Flight Service Station (FSS), which
will provide the Aviation Weather
Information Service, or AWIS (W2 in
the CFS). The Aviation Weather
Briefing Service (AWBS), however, is
more advanced because it is used for
long range flights as well. It is not
always found at an FSS – you mostly
see it at AES offices. It is called W1
in the CFS.
The PATWAS is the Pilot's Automatic
Telephone Weather Answering Service,
which pretty much speaks for itself –
you use a touch tone telephone to
get the services you need. Check the
CFS for where you can obtain it.
Some FBOs have access to a private
system based on DUATS computer
terminals. Again, check the CFS for
availability, but you can also get it at
home on your own computer.
ATIS (Automatic Terminal Information
Service) is typically broadcast on a
VOR frequency at major
aerodromes (you can use it as an ID
on instrument rides), although it may
have its own channel. You should
listen to it and take down the details
before you contact ATC.
NDB stations are used to broadcast
Transcribed Weather Broadcasts (TWB),
which may also contain NOTAMs.
VOLMET is usually transmitted
over HF for long-distance flights
(North Atlantic and Arctic for
Canada), but can be found
elsewhere. It consists of long
readouts of TAFs and METARs in a
sequence, so if you miss the
aerodrome you want, just wait for it
to come round again.
Otherwise, you may find:
The GFA
The Graphic Area Forecast was
introduced in April 2000. It’s not
one, but a series of six charts
(actually, three sets of two) showing
the most probable weather below
24,000 feet amsl at a particular time
for a particular region, which could
be Arctic, Yukon-Northwest Territories,
Nunavut, Pacific, Prairie, Ontario-Quebec
and Atlantic. There is one for the
ocean West of the Arctic, but you
only get that if you ask for it. They
are issued four times a day, about
half an hour before the periods they
relate to, which are 0000, 0600, 1200
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