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to Liberal, Kansas to Dove Creek, Wyoming to
Rocksprings, Wyoming, and back to Bozeman. As
mentioned previously under the header, the valid time
begins on the 14th day of the month at 1100Z for a 12-
hour period. A broken to overcast cloud layer begins
between 7,000 to 9,000 feet MSL, with tops extending
to 20,000 feet. Since visibility and wind information is
omitted, the visibility is expected to be greater than 6
statute miles and the wind less than 20 knots. However,
the visibility (VSBY) is forecast to be occasionally 3
miles in light rain and fog (3R-F). After 2000Z, widely
scattered thunderstorms with light rain showers are
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expected, with cumulonimbus (CB) cloud tops to
45,000 feet. The 6-hour categorical outlook covers the
period from 2300Z on the 14th to 0500 on the 15th. The
forecast is for marginal VFR weather due to ceilings
(CIG) and rain showers (RW).
CONVECTIVE OUTLOOK CHART
The convective outlook chart (AC), is a two-panel chart
that forecasts general thunderstorm activity for the
valid period of the chart. ACs describe areas in which
there is a risk of severe thunderstorms. Severe thunderstorm
criteria include winds equal to or greater than 50
knots at the surface or hail equal to or greater than 3/4
inch in diameter, or tornadoes. Convective outlooks are
useful for planning flights within the forecast period.
Both panels of the convective outlook chart qualify the
risk of thunderstorm activity at three levels, as well as
areas of general thunderstorm activity.
Slight (SLGT)—implies well-organized severe thunderstorms
are expected but in small numbers
and/or low coverage.
Moderate (MDT)—implies a greater concentration of
severe thunderstorms, and in most cases greater
magnitude of severe weather.
High (HIGH)—means a major severe weather outbreak
is expected, with a greater coverage of severe
weather with a likelihood of violent tornadoes
and/or damaging high winds.
General thunderstorm activity is identified on the chart
by a solid line with an arrowhead at one end. This indicated
that the area of general thunderstorm activity is
expected to the right of the line from the direction of
the arrowhead.
The left panel [Figure 9-54] describes specific areas of
probable thunderstorm activity for day-1 of the outlook.
The day-1 panel is issued five times daily, starting
a 0600Z and is valid from 1200Z that day until
1200Z the day after. The other issuance times are
1300Z, 1630Z, 2000Z, and 0100Z and are valid until
1200Z the day after the original issuance day.
The right panel [Figure 9-55] is the day-2 chart, it is
issued twice daily. The initial issue is 0830Z standard
time, 0730Z daylight time and is updated at 1730Z.
The valid time of the chart is from 1200Z following
the original issue of the day-1 chart until 1200Z of the
next day. For example, if the day-1 chart is issued on
Monday it is valid until 1200Z on Tuesday, subsequently
the day-2 chart is valid from 1200Z Tuesday
until 1200Z on Wednesday.
WINDS AND TEMPERATURES
ALOFT FORECAST
Awinds and temperatures aloft forecast (FD) provides
an estimate of wind direction relation to true north,
wind speed in knots and the temperature in degrees
Celsius for selected altitudes. Depending on the station
elevation, winds and temperatures are usually
forecast for nine levels between 3,000 and 39,000 feet.
Information for two additional levels (45,000 foot and
53,000 foot) may be requested from a FSS briefer or
NWS meteorologist but is not included on an FD.
[Figure 9-56]
The heading begins with the contraction FD, followed
by the four-letter station identifier. The six digits are
the day of the month and the time of the transmission.
The next two lines indicate the time of the observation
and the valid time for the forecast. In the example, the
observation was taken on the 15th day of the month at
1200Z, is valid at 1800Z, and is intended to be used
between 1700Z and 2100Z on the same day.
The first two numbers indicate the true direction from
which the wind is blowing. For example, 1635-08
indicates the wind is from 160° at 35 knots and the
temperature is –8°C. Determining the wind direction
and speed and temperature requires interpolation
Figure 9-54. Day-1 panel of the Convective Outlook Chart. between two levels. For instance, to determine the
Figure 9-55. Day-2 panel of the Convective Outlook Chart.
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wind direction and speed for a flight at 7,500 feet over
Hill City (HLC), a good estimate of the wind at 7,500
　
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