Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 171750
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1050 AM MST Sat Feb 17 2018

.UPDATE...
Issued at 1039 AM MST Sat Feb 17 2018

We are seeing a considerable decrease in low-level flow across the
CWA late this morning, as confirmed by the latest VAD wind profile
for KCYS showing only around 40 knots available to mix. Local prob
guidance for high wind exceedance goes to zero after 18z. Although
mixing will be strong this afternoon, all available guidance still
points to weakening flow over the next few hours. We cancelled the
High Wind Warning including Cheyenne, but made no changes to other
headlines as gradients are expected to increase markedly this eve/
overnight over western and northern areas.

&&

.SHORT TERM...(Today and tonight)
Issued at 345 AM MST Sat Feb 17 2018

After a strong start to winds last evening, it looks like we are
in a little bit of a lull right now as Craig to Casper gradients
ease under 60mtrs. We are still seeing a few gusts to 60 mph on
WYDOT`s sensors, so will not change any wind headlines at this
time. Arctic boundary moving into north central Montana this
morning. South of the front, temperatures are in the low to mid
20s. North of the front, single digit temperatures are common
across northern Montana.

Should see winds picking up again across southeast Wyoming after
15Z or so when gradients begin to increase. 700/750mb winds over
the north Laramie Range begin to increase after 18Z, reaching 65
to 70kts by mid afternoon. Decided to upgrade the north Laramie
Range and Converse County wind watch to a warning this afternoon.
Strongest winds up there this evening when 700.750mb winds
forecast to hit 75kts across a large portion of the north Laramie
Range.

One last area for today, transitioned the Blizzard Warning around
Arlington to a High Wind Warning. We did have a period last night
when visibilities got bad out by Arlington, but do think the snow
was not widespread enough to continue the Blizzard Warning.

.LONG TERM...(Sunday through Friday)
Issued at 345 AM MST Sat Feb 17 2018

Arctic front still on track to make its way into Converse County
Sunday. Some differences in timing as the GFS is the fastest with
the ECMWF roughly 6-12 hours slower. Regardless of these
differences, it still looks like a widespread snow event is going
to take shape Sunday night into Monday night. Did add the northern
Panhandle and western half of the CWA into a Winter Storm Watch
for this timeframe. Also extended the end times of the watches to
account for the slower ECMWF by roughly 6 hours.

Really cold temperatures expected Monday as GFS 700mb temperatures
fall to -22C across our northern zones to around -12C here by
Cheyenne. Will probably be dealing with Windchill headlines Monday
night into Tuesday morning as snow ends and other headlines drop.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday morning)
Issued at 1020 AM MST Sat Feb 17 2018

VFR with lowest CIGS 5000-10000 ft AGL. Strong westerly winds with
gusts 35-50 kt will continue to be a concern for aviation operations
for southeast Wyoming through early Sunday morning, especially along
and west of the Laramie Range. Moderate to severe mountain wave
turbulence can be expected as well. The Nebraska Panhandle
terminals, except Chadron, will experience breezy west to northwest
winds gusting 25-35 kt this afternoon, diminishing and shifting to a
southerly direction this evening. There will be occasional mountain
obscurations from snow shower activity.


&&

.FIRE WEATHER...
Issued at 313 AM MST Sat Feb 17 2018

Strong winds continue today ahead of an approaching arctic front
moving into the area from the north. Will see widespread strong
winds through the day today into this evening. By Sunday late
morning, we begin to see the front move into Converse and Niobrara
Counties with winds shifting north and northeast behind the front.
Widespread moderate snow and much colder air moving in behind the
front. Just about every location in southeast Wyoming and Nebraska
panhandle are going to see snow accumulations with the most
significant along and north/west of a line from Chadron to
Wheatland to Buford. Snow continues into Tuesday before ending.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Watch from Sunday evening through Monday evening
     for WYZ106-107-109-110-112>117.

     High Wind Warning until 5 AM MST Sunday for WYZ104>107-109-110-
     113-115>117.

     Winter Storm Watch from Sunday morning through Monday evening
     for WYZ101>105.

     High Wind Warning from 3 PM this afternoon to 9 AM MST Sunday
     for WYZ101-103.

NE...Winter Storm Watch from Sunday evening through Monday evening
     for NEZ002-095.

&&

$$

UPDATE...CLH
SHORT TERM...GCC
LONG TERM...GCC
AVIATION...MAJ
FIRE WEATHER...GCC



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