Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 291154

Area Forecast Discussion
National Weather Service Cheyenne WY
454 AM MST Tue Nov 29 2016

.SHORT TERM...(Today through Thursday)
Issued at 330 AM MST Tue Nov 29 2016

An intense upper-level low pressure system remains stationary this
morning with a 982 mb surface low centered over southeastern North
Dakota at 09z. We continue to see an impressive water vapor and IR
satellite presentation with this system, with wrap-around moisture
finally pushing south into our CWA. Cooling cloud tops on infrared
imagery suggest snow showers will continue to increase in coverage
over the next few hours through the morning. The models show a 500
mb vort max backing into the Laramie Range and weakening after 18z
which should lead to decreasing precipitation chances for the High
Plains. Lingering moisture and favorable orographics will probably
allow the mountains to add on to already impressive totals, so the
consensus was to extend the Winter Storm Warning thru 00z Wed with
an additional 4-8 inches possible.

High winds are the main concern for today. A very favorable upper-
level and surface low position places a wide belt of stronger low-
level flow extending from southeast MT into much of eastern WY and
the NE Panhandle. Douglas and Lusk have already gusted near 50 MPH
this morning with the help of snow showers, and guidance shows low
level flow continuing to increase through 15-18z. The NAM/GFS both
suggest 50 to 60 knot flow at H75 over most of the CWA to the east
of I25. We were a bit skeptical of forecast soundings showing good
low-level mixing with widespread clouds today, but current obs are
telling us this will not be an issue. Plus, snow showers are quite
likely to bring stronger winds to the surface and create potential
problems with blowing snow. Consensus with neighboring WFOs was at
least 50-55 MPH wind gusts across much of the region with a decent
shot of at least a few 60 MPH gusts. MOS guidance shows many sites
in the 32-36 knot range sustained between 18-21z, which is usually
a good sign for very strong winds. We have enough confidence to go
ahead and upgrade the Wind Advisory to a High Wind Warning for the
Panhandle and also add some of the WY plains to the HWW. Our local
research says Cheyenne does not typically do well in northwesterly
flow, so for that reason we did not include KCYS at this time. The
strongest flow should be east of this zone, however. Gradients are
expected to remain strong overnight, so it will remain breezy. The
threat for high winds should end after 00z though.

It will turn very cold tonight with decreasing clouds and H7 temps
around -14 deg C over much of the area. Lows will likely be in the
single digits along and west of the Laramie Range where there will
be less wind/mixing. Precipitation chances will increase again for
Thursday as the next mid-level disturbances approaches western Wyo
late in the forecast period, mainly for western zones.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM MST Tue Nov 29 2016

Cold temperatures are going to stay with us through the extended
and we will be dealing with periods of snow as a series of
shortwaves moves through the area.

First one set for Thursday afternoon/evening that will mainly be
confined along and west of the Laramie Range. Did carry a small
chance for snow here at Cheyenne. Best lift and upper diffluence
though further west.

Much stronger system set to move into western Wyoming Sunday. This
one may need winter headlines for the Snowy and Sierra Madre
Ranges. Should be a pretty prolonged event that could persist
through Tuesday, similar to this past system.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 452 AM MST Tue Nov 29 2016

IFR at a few locations this morning with passing snow showers.
Main story will be winds today with gusts to 50kts likely in the
Panhandle. Expact these winds to continue into the mid afternoon
before easing towards sunset.


Issued at 142 AM MST Tue Nov 29 2016

No fire weather concerns with cool temperatures and resulting high
RH values. Strong winds are expected today across southeast WY and
the western NE Panhandle with frequent gusts between 50-60 MPH.


WY...High Wind Warning from 8 AM this morning to 5 PM MST this
     afternoon for WYZ101-102-107-108-119.

     Winter Storm Warning until 5 PM MST this afternoon for WYZ112-

NE...High Wind Warning from 8 AM this morning to 5 PM MST this
     afternoon for NEZ002-003-019>021-054-055-095-096.



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