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The FA consists of several sections: a communications
and product header section, a precautionary statement
section, and two weather sections (synopsis and VFR
clouds and weather). Each area forecast covers an 18-
hour period. [Figure 9-53]
COMMUNICATIONS AND PRODUCT HEADERS
Refer to figure 9-53 for the following discussion. In
the heading SLCC FA 141045, the SLC identifies the
Salt Lake City forecast area, C indicates the product
contains clouds and weather forecast, FA means area
forecast, and 141045 is the date time group and indicates
that the forecast was issued on the 14th day of the
month at 1045Z. Since these forecasts times are
rounded to the nearest full hour, the valid time for the
report begins at 1100Z. The synopsis is valid until 18
hours later, which is shown as the 15th 0500Z. The
clouds and weather section forecast is valid for 12-
hour period, until 2300Z on the 14th. The outlook portion
is valid for six hours following the forecast, from
2300Z on the 14th to 0500Z on the 15th. The last line
of the header lists the states that are included in the Salt
Lake City forecast area.
Amendments to FAs are issued whenever the weather
significantly improves or deteriorates based on the
judgment of the forecaster. An amended FA is identified
by the contraction AMD in the header along with
the time of the amended forecast. When an FA is corrected,
the contraction COR appears in the heading,
along with the time of the correction.
PRECAUTIONARY STATEMENTS
Following the headers are three precautionary statements,
which are part of all FAs. The first statement
alerts the pilot to check the latest AIRMET Sierra,
which describes areas of mountain obscuration which
may be forecast for the area. The next statement is a
reminder that thunderstorms imply possible severe or
greater turbulence, severe icing, low-level wind shear,
and instrument conditions. Therefore, when thunderstorms
are forecast, these hazards are not included in
the body of the FA. The third statement points out that
heights, which are not MSL, are noted by the letters
AGL(above ground level) or CIG (ceiling). All heights
are expressed in hundreds of feet.
SYNOPSIS
The synopsis is a brief description of the location and
movement of fronts, pressure systems, and circulation
patterns in the FA area over an l8-hour period. When
appropriate, forecasters may use terms describing ceilings
and visibility, strong winds, or other phenomena.
In the example, high pressure over northeastern
Montana will continue moving gradually eastward. A
low-pressure system over Arizona, New Mexico, and
western Texas will remain generally stationary. Aloft
(ALF), a trough of low pressure extending from western
Montana into southern Arizona is expected to
remain stationary.
VFR CLOUDS AND WEATHER
The VFR clouds and weather portion is usually several
paragraphs long and broken down by states or geographical
regions. It describes clouds end weather,
which could affect VFR operations over an area of
3,000 square miles or more. The forecast is valid for
12 hours, and is followed by a 6-hour categorical outlook
(18 hours in Alaska).
When the surface visibility is expected to be six statute
miles or less, the visibility and obstructions to vision
are included the forecast. When precipitation, thunderstorms,
and sustained winds of 20 knots or are forecast,
they will be included in this section. The term
OCNL (occasional) is used when there is a 50 percent
or greater probability, but for less than 1/2 of the forecast
period, of cloud or visibility conditions which
could affect VFR flight. The area covered by showers
or thunderstorms is indicated by the terms ISOLD (isolated),
meaning single cells. WDLY SCT (widely scattered,
less then 25 percent of the area), SCT or AREAS
(25 to 54 percent of the area), and NMRS or WDSPRD
(numerous or widespread, 55 percent or more of the
area).
The outlook follows the main body of the forecast, and
gives a general description of the expected weather
using the terms VFR, IFR, or MVFR (marginal VFR).
A ceiling less than 1,000 feet and/or visibility less than
3 miles is considered IFR. Marginal VFR areas are
those with ceilings from 1,000 to 3,000 feet and/or visibility
between 3 and 5 miles. Abbreviations are used
to describe causes of IFR or MVFR weather.
In the example shown above, the area of coverage in
the specific forecast for Wyoming and Colorado is
identified using three-letter designators. This area
extends from Bozeman, Montana to Gillette, Wyoming
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Glider Flying Handbook(132)
