Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 142110

Area Forecast Discussion
National Weather Service Cheyenne WY
310 PM MDT Wed Mar 14 2018

.SHORT TERM...(Tonight through Friday evening)
Issued at 300 PM MDT Wed Mar 14 2018

Active weather expected late this week as a Pacific storm system
redevelops across the plains Thursday night and into Friday. As
for tonight and early Thursday morning, benign weather is
expected to continue with perhaps a few rain showers developing
after midnight from Carbon county northeastward towards Converse
and Niobrara counties. Otherwise, High temperatures will likely
occur earlier in the day on Thursday with readings in the 50`s to
low/mid 60`s across western Nebraska and the eastern plains.
Expect cooler temperatures to move into the region late Thursday
afternoon as the initial cold front moves across the area.

Made no changes in the current headlines today with some model
disagreement observed, mainly with the evolution of the storm and
speed of cooling. Expect precipitation to develop Thursday
afternoon across most areas, especially along and east of I-25 as
the initial shortwave trough lifts northeast and begins to stall
across northern Colorado. Models show Impressive upper level
diffluence as a 100 kt jet lift northward over Wyoming and stalls.
Most of southeast Wyoming (along and east of I-25) and western
Nebraska are in this area of peak diffluence. In addition, LI`s
will be 0c to -2c with good llvl convergence an frontogenesis.
Added thunderstorms to the forecast for this area, mainly along
and just north of I-80 since model soundings are showing around
500 j/kg of CAPE which may resulting in widely scattered
thunderstorms in the area. Would not be surprised if a few
thunderstorms contained some gusty winds and small hail, but this
should be very isolated.

Tricky forecast expected for Thursday night and Friday with
several last minute changes possible in regards to snow
accumulation, precipitation type, and wind impacts. GFS, NAM, and
Canadian are a bit more progressive with the shortwave
disturbance and are therefore further east with forecasted
cyclogenesis. The ECMWF and the SREF tend to slow the system down
quite a bit earlier, which will lead to more snowfall across the
high plains as the cold air will have have time to settle across
the region and winds will be more north and northeast off the
surface. Another issue is snowlevels for east central wyoming and
northern Nebraska. Some models show the cold air taking its time
through Thursday night which may present a problem for the lower
elevations as snow might not stick to the roadways. Tweaked snow
accumulations for this area, with lower amounts below 4000 feet
but kept amounts higher for the Pine Ridge. Further west, the
arrival of cold air and the specific location of the precipitation
shield will mean the difference between a trace of snow and
several inches. After collaboration with WPC, increased
accumulations in these areas based on the more aggressive ECMWF
and SREF which have been consistent over the last 24 hours. By
early Friday morning, rapid cyclogenesis and strong winds aloft
will result in strong downslope winds. Kept the High Wind Watch
going for areas outside the Winter Storm Watch in southeast
Wyoming since the ECMWF solution produces lower wind speeds across
the area, although blowing and drifting snow may become more of a
concern in this case.

Thankfully, conditions look to improve by Friday afternoon as the
storm system nudges eastward during the day. It will remain cool
and windy for southeast Wyoming and the southern Nebraska

.LONG TERM...(Friday night through Tuesday)
Issued at 307 AM MDT Wed Mar 14 2018

Lull in the weather Friday night into Saturday as a short upper
ridge moves by with milder temperatures returning on Saturday.
Some snow showers should return to western areas Saturday night
as the next upper trough approaches the CWA. Models diverge on the
track of the system Sunday with the GFS to the north of the CWA
and the EC to the south. This will impact pcpn/temps over the
plains Sunday with the EC colder and bringing another round of
snow while the GFS remains dry and mild. Will lean more towards
the wetter EC for now. System moves away Sunday night with Monday
and Tuesday looking mainly dry and a bit on the cool side under
northwesterly upper flow.


.AVIATION...(For the 18Z TAFS through Thursday morning)
Issued at 307 AM MDT Wed Mar 14 2018

VFR will prevail through the period with some high clouds later
today through tonight. The only exception will be KRWL which may
drop to MVFR CIGS after 09z tonight. Otherwise, it will be breezy
this afternoon at KRWL and KLAR with gusts to 25 kt.


Issued at 307 AM MDT Wed Mar 14 2018

Warm and dry today as high pressure remains over the area.
Temperatures today climbing into the 60s and low 70s with
afternoon humidity falling to the upper teens. Fortunately, winds
are expected to be light, mitigating any fire weather concerns.
Weather changes Thursday as a low pressure system tracks across
Colorado. Expecting increasing chances for rain and mountain snow
as Thursday progresses. Snow Thursday night into Friday for all



WY...Winter Storm Watch from late Thursday night through Friday
     afternoon for WYZ102.

     High Wind Watch from late Thursday night through Friday morning
     for WYZ110-115.

     Winter Storm Watch from Thursday evening through Friday morning
     for WYZ116-117.

     High Wind Watch from Friday morning through Friday afternoon for

NE...Winter Storm Watch from late Thursday night through Friday
     afternoon for NEZ002-003-095-096.



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