Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 150535
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1035 PM MST Thu Dec 14 2017

.UPDATE...
Issued at 820 PM MST Thu Dec 14 2017

Quick update here this evening to upgrade southwest Platte County
(ie. Bordeaux area) to a High Wind Warning. Latest HRRR output
sends ribbon of low-level subsidence into this area overnight and
Friday. Was concerned earlier with winds from 300 degrees (less
favorable), but these have since backed to 280 (more favorable).
This in combination with 750mb flow of 45-50 knots were sufficient
indicators for confidence to be enough to issue the warning.
Otherwise, inherited forecast on track this evening.

&&

.SHORT TERM...(This evening through Saturday Night)
Issued at 232 PM MST Thu Dec 14 2017

Latest water vapor loop was showing drier air starting to filter
into southeast Wyoming behind a departing mid level shortwave.
This will continue to allow the snow showers to dissipate through
the remainder of the afternoon. Meanwhile, a band of stronger mid
level winds are expected to push through Montana late tonight into
tomorrow. As this band of stronger wind speeds move through this
region, it will cause the low level height/and pressure gradients
to tighten along the Laramie Range and Arlington late tonight into
Friday. As a result, we went ahead and upgraded the High Wind
Watches to Warnings across Arlington and the Laramie Range late
tonight into Friday. Hung on to a High Wind Watch for Bordeaux
since it appears the subsidence will be less favorable in that
region, and the surface trof tends to hang on in that region.
Later shifts will need to keep an eye on this potential.
Temperatures will be much warmer than today, due to good downslope
affects.

The next concern will be the shortwave now approaching the
Pacific northwest. This feature is expected to dive south during
the next couple of days. If this trend continues it will keep the
bulk of the snow across western Wyoming. We will have to watch
Carbon county especially Saturday and Saturday night especially if
that area ends up having a longer period of upper level
diffluence. The other concern will be the potential for deep low
level moisture developing behind the cold front. This will result
in lesser snow amounts mainly east of the Laramie Range. However,
it could be in the form or light snow/freezing drizzle which may
still cause some impacts Saturday night into Sunday morning
especially in the southern Nebraska Panhandle.

.LONG TERM...(Sunday through Thursday)
Issued at 232 PM MST Thu Dec 14 2017

Things should begin to clear out on Sunday with some upper level
ridging developing over the region early next week. This will
allow for a gradual warmup early next week, before another strong
cold front plows through the region Wednesday night into Thursday.
This front may bring some more snow along with it, but it does not
look like a significant snow maker.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1034 PM MST Thu Dec 14 2017

VFR conditions to prevail at area terminals through the period as
few-sct upper level clouds stream thru the area. More importantly
to airfield operations will be developing gusty winds after 07z at
RWL, after 10z at CYS/LAR, and after 17z at western Nebraska
sites. West wind gusts of 25-35 knots will be standard after these
times. Winds will persist thru the end of this TAF cycle before
decreasing Friday evening.

&&

.FIRE WEATHER...
Issued at 232 PM MST Thu Dec 14 2017

Elevated fire weather concerns are possible tomorrow due to strong
west winds developing. However, minimum humidites will most likely
range from 15 to 20 percent which will limit any red flag
potential. Beyond that timeframe we are looking a period of colder
conditions will some potential for snowfall this weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning until 9 PM MST Friday for WYZ106-110-116-117.

NE...None.

&&

$$

UPDATE...CAH
SHORT TERM...REC
LONG TERM...TJT
AVIATION...CAH
FIRE WEATHER...REC



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