Flight Training - March 2013 - 41

regular surface reports from automated
weather instruments at airports and other
locations. These include temperatures,
atmospheric pressures, humidity, wind
speeds and direction, visibility, what kind
of precipitation—if any—is falling, and
the ceiling, which is the height above the
ground of the lowest clouds that cover at
least five-eighths of the sky.
Weather satellite and weather radar
images also supply information on current weather. For vital upper atmospheric
data, forecasters rely on information from
weather balloons that are launched twice a
day and continuous, automated reports of
atmospheric pressure, temperatures, and
wind speeds and directions from many
airliners. Pilot radio reports of current
weather radioed to flight service stations
add to the data flow.
All of this data goes to the NWS Center
for Weather and Climate Prediction in
College Park, Maryland (and similar
centers in other parts of the world), where
supercomputers programmed with forecasting models use the data to produce a
huge variety of forecasts as tables of data,
words, and various kinds of weather maps.
One of the first things you need to
understand is which weather products are
reports of past data and which are forecasts. Meteorologists call a map based on
reports of the actual weather at a certain
time in the past an analysis. Maps and
words presenting forecasts of the weather
at a particular time or times in the future
are called progs, for prognosis.
FORECASTS DON’T AGE WELL. The
National Service makes some kinds of
forecasts for days and even months ahead,
but the only pilots who need an aviation
weather forecast for more than a half-day
ahead are those planning long overocean flights. This is just as well: A basic
principle of weather forecasting is that the
further ahead the forecast is for, the higher
the probability it will turn out to be wrong.
Many of the longer-range forecasts—
such as a NWS general forecast for the
public for five days ahead—will say something such as “afternoon showers” without
attempting to say when the showers are

THIS IS THE
track of Hurricane
Sandy during
the 2012 Atlantic
hurricane season
(right).
The points show
the location of
the storm at
six-hour intervals.
Weather balloons
(below) collect
atmospheric
pressure,
temperatures,
and wind speeds
and directions.

THE PATHS OF BIG STORMS ARE EASIER TO
PREDICT DAYS AHEAD OF TIME THAN SMALLERSCALE EVENTS SUCH AS CEILING AND VISIBILITY.

likely to begin and end. That’s OK. No one
should be making important decisions
based on such a forecast that far ahead
of time. Pilots need much more specific
information, but they need it for maybe
five hours—not five days—in the future.
PREDICTIONS ARE GETTING BETTER,
NOT PERFECT. The National Hurricane
Center predicted five days in advance that
Hurricane Sandy would come ashore in
southern New Jersey on October 29, 2012,

with major wind and flood damage from
New England to Maryland. In some ways,
the paths of big storms such as Sandy are
easier to predict days ahead of time than
smaller-scale events such as the ceiling
and visibility at a particular airport at a
certain time. This is because large-scale
weather patterns, such as jet stream winds
across North America and the Atlantic,
affect the paths of storms such as Sandy.
These are often more predictable than the
smaller-scale factors that affect local ceiling and visibility.
Local ceiling and visibility are easier to
forecast at certain times than at others. For
example, if you’re making a cross-country
flight on a day when a large surface highpressure area is dominating the region,
a terminal aerodrome forecast (TAF) for
your destination is likely to hold up well
for a few hours. If the weather is forecast
to change as an extratropical storm moves
toward the area, on the other hand, you
should be alert for poorer visibility or a
lower ceiling if the storm moves faster
than expected.
THE STANDARD BRIEFING. Learning how
to collect weather information for flights
begins with becoming familiar with the
FAA’s Standard Weather Briefing. Such
a briefing ensures you will obtain the
required information. The elements are:

MARCH 2013 FLIGHT TRAINING

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Flight Training - March 2013

Table of Contents for the Digital Edition of Flight Training - March 2013
