Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 130542
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1040PM MST Mon Feb 12 2018

.SHORT TERM...(This evening through Wednesday night)
Issued at 300 PM MST Mon Feb 12 2018

Forecast challenges deal with a widespread strong wind event and
heavy mountain snow.

Currently...East to southeasterly upsloping flow across the
Nebraska Panhandle up to the Laramie Range this afternoon. Even
have easterly winds west of the Laramie Range across Carbon and
Albany Counties. Arctic boundary lays from northwestern Kansas
across central Colorado up into northeastern Utah this afternoon.
Weak shortwave seen on water vapor imagery this afternoon across
northwestern Colorado moving into south central Wyoming. It is
enhancing cloud tops across Carbon County. Webcam imagery showing
lower visibilities out by Arlington and Cooper Cove, so do feel
snow is increasing out that way. SNOTELS in the Snowy and Sierra
Madre Ranges are reporting snowfall with 2-3 tenths already
reported. Should see the snow increasing across the mountains as
the afternoon continues.

Upper shortwave moves through Tuesday morning and we should see a
decrease/lull in the snow across the mountains. Winds on the
increase Tuesday as GFS 700mb winds increase to 45kts across
Carbon/Albany Counties by 21Z and then up to 50kts after 00Z.
Craig to Casper 850/700mb height gradients on the rise as well, up
to 50/53 mtrs by 00Z and 66/64mtrs respectively at 03Z. By 12Z
Wednesday, GFS 700mb winds up to 65-70kts across a wide area of
southeast Wyoming with the arctic boundary well east into South
Dakota. Do believe we are going to see a widespread high wind
event for much of southeast Wyoming during the early morning
through the afternoon hours Wednesday. MAV MOS guidance for LAR
up to 40kts sustained late morning Wednesday with NAM showing
38kts. Tried timing the watches with the wind prone areas starting
around 00Z Wednesday, Laramie and south Laramie Range as well as
Rawlins towards midnight and then Cheyenne and Douglas towards
sunrise.

Finally, another mountain snow event beginning Wednesday afternoon
and persisting into Thursday that we will need to keep an eye on.
ECMWF showing over .7 inches QPF over the mountains which would
lead to heavy snow fall out that way. Still have some time on that
event and concentrated mostly on the strong winds.

.LONG TERM...(Thursday through Monday)
Issued at 300 PM MST Mon Feb 12 2018

Thursday...Shortwave trough aloft and cold front passage will
produce a chance of snow along with much colder temperatures. Not a
lot of snow accumulation expected at this juncture based on
projected lift.

Friday...Not quite as cold as the airmass moderates slightly.
Continued windy per progged low and mid level gradients. Dry with
lack of low and mid level moisture.

Saturday...Expect a decent warming trend as the flow aloft turns
zonal aiding in a developing surface lee trough. Rising heights and
thicknesses will make for temperatures to climb into the mid 40s to
lower 50s at lower elevations.

Sunday...Another shortwave trough aloft and cold frontal passage
will produce a colder day along with a chance of snow for some
locations.

Monday...Cold and unsettled day with a chance of snow as a deep
trough aloft prevails with cold surface high pressure across the
western high plains. Maximum temperatures only in the teens and 20s
with progged 700 mb temperatures near -21 Celsius.

&&

.AVIATION...(For the 06Z TAFS through Tuesday evening)

Light snow or flurries will end over the next few hours, although
some patchy fog is expected across western Nebraska before high
clouds move into the region. Winds will be mostly light and variable
with VFR conditions expected by mid-Tuesday morning.  Windy
conditions are expected west of I-25, mainly impacting KLAR and KRWL
Tuesday afternoon.

&&

.FIRE WEATHER...
Issued at 300 PM MST Mon Feb 12 2018

Windy period upcoming for southeast Wyoming and Nebraska Panhandle
beginning Tuesday and persisting into Wednesday with most of
Wyoming fire zones hitting 60+ mph winds. Nebraska zones likely to
see wind gusts up to 45 mph. This is due to a low pressure system
tracking across northern Wyoming during that time. Winds easing
Wednesday afternoon. Fortunately, temperatures remain cool and
afternoon humidity remains well above critical levels, so fire
weather concerns should be minimal. Another high winds event
expected Friday night into Saturday, but this one will also have
widespread snow accompanying the winds.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...High Wind Watch from late Tuesday night through Wednesday
     afternoon for WYZ107-109-115>117.

     Winter Weather Advisory until 5 AM MST Tuesday for WYZ112.

     High Wind Watch from Tuesday evening through Wednesday afternoon
     for WYZ104>106-110.

     High Wind Watch from Wednesday morning through Wednesday
     afternoon for WYZ101-118.

NE...None.
&&

$$

SHORT TERM...GCC
LONG TERM...RUBIN
AVIATION...TJT
FIRE WEATHER...GCC



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