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RPRT report WK weak
RSG rising WLY westerly
RUE rough WND wind
RVR river WRM warm
S south WS wind shear
SCT scattered WV wave
SCTR sector WX weather
SE southeast XCP except
SELY southeasterly XT extend
SEC surface XTDG extending
SH shower XTRM extreme
SHFT shift XTSV extensive
SHEFO shifting ZULU(Z) UTC
SFILW shallow
Charts
Weather information is issued in
many ways, including the charts
mentioned below. Those showing
expected patterns are prognosis charts,
but they won't be anything like what
you see when you get there.
Surface Weather
These are made up from station
reports, using symbols to represent
fronts, air masses, etc. Those based
on actual data are analysis charts,
which cover up to 3,000 feet and
anything you can see from the
surface at whatever level.
They are based on observations
made at 00, 06, 12 and 18Z, and
actually issued 2-3 hours after that,
so will be quite old by the time you
depart (exam question).
152 Canadian Professional Pilot Studies
The Station Circle
Weathermen use a station circle (or
model) to describe the weather where
their observations are made.
Here is a decode:
N Total cloud
dd True wind direction
ff Wind speed in knots
VV Visibility in miles
ww Present weather
W Past weather
PPP Pressure in mb
TT Air temperature
Nh Sky covered by low or middle
cloud
CL Low cloud
h Cloudbase
CM Middle cloud
CH High cloud
TdTd Dewpoint
a Barograph trend
pp Pressure in last 3 hrs
RR Precipitation
Rt Time precipitation began or
ended
In the example below, the dark circle
below means the sky is covered with
cloud (it would have white and black
quadrants otherwise):
The temperature is 22°C, and the
dewpoint 16°C. The wind is from
the East at 15 kts – if the wind is
calm, there will be a second circle
around the first. The visibility is 10
sm in rain. The middle cloud is 3/10
Alto-Cu at 10,000 feet. Low cloud is
5/10 Cumulus at 4,000. The sea level
pressure is 1009.6 and the trend over
the last 3 hours is a steady increase
of 1.6 mb.
Front Passage
You can tell the position of fronts
between stations just by looking at
the station circles. These items will
change as a front goes by:
· Wind veers (marked clockwise
change in arrow direction).
· Pressure drops as fronts
approach, steadying after a
warm front and rising after a
cold front.
· Temperature changes according to
the type of front.
· Weather will start with moderate
continuous rain ahead of the
warm front to drizzle in the
warm sector, followed by
heavier intermittent or
continuous precipitation at the
cold front, then nil (or showers)
afterwards.
· Clouds follow the pattern in the
diagram above.
· Visibility improves significantly
behind the cold front.
So, if somebody asked you to give
reasons why you would suspect a
front in any position on a map, you
would check the above elements.
Weather 153
Upper Level Charts
These are also prognosis or analysis
charts, but based on a particular
pressure level, so the real altitude
represented will vary a great deal
(they will be lower as you go North,
because it gets colder there). Here
are the approximate heights:
Pressure(mb) Height ASL (ft)
850 5,000
700 10,000
500 18,000
400 24,000
300 30,000
The idea is to get a 3D picture of
what's going on upstairs. Although
the isobars look the same, and the
wind will behave the same way,
remember the surface chart is based
on sea level pressure.
Analysis Charts
Come out at 00 and 12Z each day.
The 850 mb chart has contours at 60
metre intervals, starting at 1500, with
isotherms every 5°C. Fronts are
usually shown in their surface
position (they are not shown on the
700 mb chart).
Prognostic Charts
Cover between FL 100-250, based
on 700-400 mb pressure levels. They
forecast moderate to severe icing,
significant cloud layers, mountain
waves, freezing levels at 10,000 feet
and the surface position of highs and
lows. Wind pennants are triangular
for 50 kts.
Spot temperatures (negative unless
otherwise noted) are in circles.
The relevance of upper level charts
is that they give you a better idea of
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