Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 141701
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1000 AM MST Tue Nov 14 2017

.SHORT TERM...(Today through Wednesday night)
Issued at 357 AM MST Tue Nov 14 2017

Shortwave trough over eastern Oregon early this morning will track
east northeast and into eastern Montana by this evening. Upper
jet max associated with this feature will sink southeastward into
southeast Wyoming by this afternoon. At the surface, a trailing
cold front will cross the area from west to east this afternoon
and early evening. Brief ridging will build over the Rockies
behind the departing shortwave tonight and Wednesday.

Main concerns this period will be windy conditions associated
with the front this afternoon. Winds in the 2 to 5 kft layer
increase to around 45kt out of the NW in the post frontal
environment late this afternoon. While this is not necessarily a
favorable direction for high winds in the wind prone areas, deep
mixing should produce rather widespread gusts of 50 to 55 mph west
of the Laramie Range this afternoon. Subsidence behind the front
as well as increasing flow just off the surface should also
contribute to a period of very windy conditions for the Cheyenne
area late this afternoon. Gusts to 50 mph out of the NW behind the
front seem likely in this area for a time as well. Would not be
surprised to see a few gusts to high wind criteria this afternoon
but think the duration and spatial coverage of any such gusts do
not warrant a wind headline at this time. Day shift can monitor
observational and satellite trends for this potential and issue if
necessary.

Winds will die down quickly this evening with mid and high clouds
diminishing. Temps will cool quickly well into the 20s after another
very warm day today. Wednesday will be sunny to partly cloudy and
cooler but much less windy with highs in the upper 40s to mid 50s.

.LONG TERM...(Thursday through Tuesday)
Issued at 357 AM MST Tue Nov 14 2017

Progressive pattern will continue through at least early next
week, with some indication of a more amplified and stagnant
pattern developing in time for Thanksgiving. Before then, the
main impacts during this period will fall on Thursday and Friday as
a positively tilted shortwave scoots across the intermountain west.
Concerns for Thursday and Thursday night center around high wind
potential mainly in the typical high wind corridors of southeast
Wyoming (Arlington, Bordeaux, I80 Summit). Mid/upper- level
southwest flow couples with low-level gradient coincident with
daytime mixing. H7 wind progs of 50-65 knots along with critical
KCAG-KCPR gradients further point to high wind potential. Still too
far out for any sort of highlight, but have continued increasing
winds. It would seem that the slower ECMWF solution from 24 hours
ago has offered the most run-to-run consistency, which has been
further support by latest GFS trends. Even so, should see
precipitation begin to work into the Carbon County as early as
Thursday evening, but moreso after midnight. In the pre-frontal air
mass, snow-levels will still be high. Cold front moves N-S on
Friday. The colder air mass will drop snow- levels to between 5000-
6000 feet by late Friday morning and especially during the afternoon
turning precip over to snow. High temps will likely be reached in
most areas Friday morning. Best snow looks to be confined to the
Snowy and Sierra Madre Ranges with increasing confidence perhaps up
to around a foot of new snow there. Although some snow will be
possible in lower elevations (especially around Arlington and in
potential convective banding over the plains), think the bigger
story Friday will be a brief period of strong post-frontal bora
winds. Wind speeds of 40-55 knots at the top of the mixed layer
suggest high wind potential along the I80 corridor as well as for
areas along and west of the Laramie Range.

System departs quickly late Friday bringing an end to any
lingering snow Friday evening. The breezy-windy conditions look to
remain through the weekend and into early next week though. For
now low-level gradients suggest the potential for periodic bouts
of high wind in favored locations, but generally should remain
below. Otherwise, the dry conditions are expected to remain thru
the first half of next week.

The coolest air mass will exist Friday/Saturday (still only around
seasonal normals), with temperatures moderating back into the 50s
east Sunday-Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday morning)
Issued at 1000 AM MST Tue Nov 14 2017

VFR. SCT-BKN CIGS AOA 15000 FT AGL through early evening. West to
northwest surface winds will be breezy with gusts of 25-35 KT at
southeast Wyoming terminals and 20-25 KT at western Nebraska
terminals. Winds will subside later this evening.

&&

.FIRE WEATHER...
Issued at 357 AM MST Tue Nov 14 2017

Some elevated fire weather conditions are possible this afternoon
east of the Laramie Range in areas where fuels may be receptive.
RH values will lower to around 20 percent along with gusty W to NW
winds. Cooler temperatures on Wednesday along with less wind will
mitigate any fire weather threat.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

SHORT TERM...DEL
LONG TERM...CAH
AVIATION...MAJ
FIRE WEATHER...DEL



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