Area Forecast Discussion
Issued by NWS Cheyenne, WY

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348
FXUS65 KCYS 180509
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1009 PM MST Tue Jan 17 2017

.SHORT TERM...(This evening through Thursday)
Issued at 157 PM MST Tue Jan 17 2017

The main concern during this timeframe will be the strong winds
around Bordeaux through tomorrow and the potential for fog in
valleys again tonight.

Latest surface analysis was showing strong high pressure over
southern Wyoming where a deep snowpack continues to exist.
Meanwhile, the lee side trof has continued to strengthen this
afternoon. HiRes short range models have been really struggling
with temperatures today over the snowfield in southern Wyoming and
northern Colorado. The models are trying to warmup this snowpack
much too quickly. Meanwhile, areas east of this snowpack,
temperatures climbed to the upper 30s to the 40s this afternoon
which is a tad warmer than progged by the short range models. As
a result, this is a resulting in a tighter pressure/thermal gradient
this afternoon, and has caused wind speeds near our gap region
near Bordeaux to reach high wind warning criteria today. Would
anticipate these wind speeds to slacken during the evening as this
pressure/thermal gradient weakens. However, these wind speeds
should pick back up again tomorrow morning into the afternoon due
to the same conditions as today. As a result, we kept the high
wind warning for going for Bordeaux through Wednesday. It may also
get a little gusty along the foothills of the Laramie Range
Wednesday afternoon where some decent mixing will commence.

The next concern is the temperatures and fog potential again
tonight. Should be another good night for radiational cooling
especially over the snowpacked areas west of the Laramie Range
with even some fog west of RWL and in the Laramie Valley. We
lowered temperatures quite a bit from the Consensus Models again
with the biggest difference in the Laramie Valley.

Otherwise, mild daytime conditions are anticipated east of the
Laramie Range through Thursday with afternoon highs in the 40s and
50s. Areas to the west of the Laramie Range, are forecast to
slowly warm up to the 30s.

.LONG TERM...(Thursday night through Tuesday)
Issued at 157 PM MST Tue Jan 17 2017

A longwave trough will remain in place through the long term period
with intermittent shortwave features traversing across the western
CONUS in progressive flow. This should keep temps for our forecast
area around normal for this time of year with breezy, but not too
windy, conditions across southeast Wyoming. Mountain snow showers
will linger THursday night through Friday night as an upper trough
moves east across the central Rockies, then northeast into the
central Plains. Could see a light snow/rain shower move into the
plains as well. Shortwave ridging will then move overhead for
Saturday ahead of the next upper low sliding across the desert
southwest into the southern plains on Saturday and Saturday night.
Looks as though orographic snows will return Saturday night on the
western edge of the upper low with increasing winds aloft and
Pacific moisture. Westerly llvl downslope flow should keep much of
our eastern plains dry, however can`t rule out a light snow shower
across the northern zones near a weak sfc boundary. Another
progressive ridge will move overhead for Sunday, then a stronger
storm system is on the horizon for the early part of next week.
Still quite a few difference exist between GFS and ECMWF with this
system, but the general trend is similar between models. This means
there remains a potential for more widespread snow and colder
temperatures to the forecast area late Monday into Tuesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1002 PM MST Tue Jan 17 2017

This is the second consecutive night that the short range models
have not predicted valley fog out west. Yet, the overall synoptic
pattern suggests the potential for IFR or lower vis/cig in fog for
the western valleys, especially west of RWL and at LAR between 07Z
and 15Z. Otherwise, VFR conditions will prevail for most terminals,
with breezy southwest winds at KRWL Wednesday afternoon. Locally
stronger gap winds will be possible between Cheyenne and Wheatland
Wednesday with gusts to 50 kt.

&&

.FIRE WEATHER...
Issued at 157 PM MST Tue Jan 17 2017

Fire weather concerns will be minimal during the next few
days, due to a dense snowpack in place west of the Laramie Range.
East of the Laramie Range, it will be a bit more breezy minus the
snow cover. However, minimum afternoon humidities will generally
range from 30 to 45 percent.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning until 6 PM MST Wednesday for WYZ106.

NE...None.
&&

$$

SHORT TERM...REC
LONG TERM...RJM
AVIATION...MAJ
FIRE WEATHER...REC



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