Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 141057

Area Forecast Discussion
National Weather Service Cheyenne WY
357 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

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 aross 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 06Z TAFS through Tuesday evening)

VFR conditions to prevail tonight and Tuesday morning with
intervals of high clouds. Windy conditions are expected by late
Tuesday morning through Tuesday afternoon, especially along and west
of Interstate 25, where gusts up to 40 knots are possible.


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.





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