Flight Training - June 2014 - 45

CLOCKWISE FROM TOP LEFT: An NWS weather depiction
chart; NWS surface analysis chart; guide to the most common symbols around a weather station's location on a map
(not all of these are always used) and sometimes others are
used; weather map wind speed and direction symbols (the
dots are locations of weather stations). For a chart showing
all of the nearly 100 symbols that are sometimes used on
weather maps, go online (http://aviationweather.gov/static/
adds/docs/metars/wxSymbols_anno1.pdf.

predictions pilots should use are the
most recent ones for the times of the
flight.
Worded reports of weather data are
called observations. If the observations
are used to produce a map, the map is
called an analysis.
Worded reports and maps of forecasts
often are called "progs" (for prognoses).
The NWS produces significant weather
prog maps showing expected locations
of dangerous weather for as much as 24
hours in the future.
WEATHER DEPICTION CHARTS. If you
plan to take off in the next hour or so, you
should begin by looking at the current
weather and then turn to forecasts of
how it's expected to change. At times, a
look at the current weather could make
you decide to bag your flying plans for

that day because it's obvious that a big
storm along your route isn't going to disappear before you want to take off.
The NWS weather depiction chart (top
left) gives you a quick overview of the
weather that most affects pilots.
If you do not have an instrument rating, you must avoid the areas shown on
the chart with instrument flight rules
(IFR) conditions. These areas have ceilings below 1,000 feet and/or visibility
less than three miles. They are outlined
on the chart with a shaded area inside a
solid line. On color versions of the chart,
IFR areas are shaded in red.
You could fly legally in areas with marginal VFR without an instrument rating if
you stayed far enough away from clouds,
but marginal VFR weather could quickly
deteriorate into IFR weather.
Weather depiction charts outline
marginal VFR areas with a solid line,
but areas inside the lines are not shaded.
Marginal VFR means ceilings are 1,000
to 3,000 feet above the ground and/or
visibility is three to five statute miles.
Areas not inside a solid line on the chart

have either clear skies or ceilings higher
than 3,000 feet and visibility greater than
five miles.
The circles on the map represent airports; the shading indicates ceiling. Solid
black dots show the sky is overcast, while
all-white circles mean clear skies. Partly
shaded circles show scattered or broken
clouds. You can see that on the day the
chart was produced, IFR and marginal
VFR weather covers most of the eastern
United States.
SURFACE ANALYSIS CHARTS. While the
weather depiction chart displays areas
of IFR, MVFR, and VFR weather, surface
charts (top right) add to the picture by
showing the major weather features that
are causing those conditions.
The thin red lines on the map are
isobars, which represent areas of equal
barometric pressure. The "Ls" are centers of relatively low surface atmospheric
pressure, and the "Hs" are centers of
relatively high pressure. The most prominent weather feature on this chart is the
area of low pressure centered a little to

JUNE 2014 FLIGHT TRAINING

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http://aviationweather.gov/static/adds/docs/metars/wxSymbols_anno1.pdf http://aviationweather.gov/static/adds/docs/metars/wxSymbols_anno1.pdf

Flight Training - June 2014

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