Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 020933

Area Forecast Discussion
National Weather Service Cheyenne WY
233 AM MST Fri Dec 2 2016

.SHORT TERM...(Today through Sunday)
Issued at 300 AM MST Fri Dec 2 2016

Winds are the forecast challenge in the short term.

Currently...Water vapor imagery showing some cyclonic turning in
the flow to our west and southwest early this morning. Area METARS
are reporting low cloudiness from the Laramie Range back into
western Wyoming. Not seeing the cooling cloud tops so far this
morning. May need to pull PoPs if we do not see these cooling
cloud tops developing later this morning. Off to the northwest
across the eastern Gulf of Alaska, a powerful low pressure system
moving onshore north of Juneau. Occluded front extends from this
low with triple point just off the coast of Vancouver British

No a whole lot going on today. Weak shortwave trough seen on both
the GFS and ECMWF kicking off some snow showers over the south
Laramie Range. Kept low 20-30 percent pops in the forecast. Again,
may need to pull if we do not see indications that cloud tops are

700mb winds begin to increase Saturday morning as the trough moves
east. GFS showing 45-50kts at 700mbs across Carbon County at 12Z
Saturday. Latest WRKHGT High Wind Tool showing 850/700mb Craig to
Casper gradients increasing to 53/50 meters respectively after
12Z. GFS WRKGHT approaching 60mtrs at both levels by 15Z Saturday,
so High Wind Watch still looks good. Did add the South Laramie
Range Zone into the watch as 700mb winds forecast at 50kts over
this area tomorrow morning.

Later shifts can upgrade the watches. Will give them another
chance to look at later guidance before pulling the trigger. One
suggestion would be to extend the headline into Sunday or maybe
issue another Watch for Sunday evening as the gradients again
increase to +60mtrs after 00Z Monday.

.LONG TERM...(Sunday night through Thursday)
Issued at 300 AM MST Fri Dec 2 2016

Sunday night/Monday...Initial batch of moisture moves across our
southwest counties Sunday night producing snows across our Snowy and
Sierra Madre Ranges. The next arctic type cold front moves across
our region Monday afternoon with steady or falling temperatures in
the afternoon. Light snow increases in coverage and spreads further
east Monday afternoon, most numerous over the mountains.

Tuesday...Bitterly cold airmass filters across our region in the
wake of the passing arctic cold front and with 700 mb
temperatures plunging to near -16 to -20 Celsius, maximum
temperatures will only be in the single digits and teens. Deeper
moisture and lift will occur across our southern counties with a
chance of light snow along and south of a Rawlins to Scottsbluff

Wednesday...Light snow will come to an end as the low and mid levels
of the atmosphere dry out. Bitterly cold air continues to filter
across our counties under the cold trough aloft and with 700 mb
temperatures near -22 Celsius, high temperatures only in the single
digits and teens again.

Thursday...ECMWF and GFS differ considerably with respect to a
warming trend. The GFS shows northwest flow aloft while the ECMWF
continues with north flow aloft. 700 mb temperatures vary from near
-10 Celsius on the GFS to -22 Celsius on the ECMWF. GFS shows a high
temperature of 31 degrees in Cheyenne while the ECMWF has 12
degrees. Tend to believe the colder ECMWF solution for now with the
cold, dense air hard to erode, but for now will continue to blend
with our neighbors who favor the warming trend. Nevertheless, this
day will be dry with limited low and mid level moisture and no lift.


.AVIATION...(For the 06Z TAFS through 06Z Friday evening)
Issued at 950 PM MST Thu Dec 1 2016

Periodic snow showers will continue tonight and Friday morning along
and west of Interstate 25. The showers will lower ceilings and
visibilities to MVFR at times at RWL, with mountain obscurations.
Otherwise, cloud cover will increase from west to east, with
ceilings between 5000 and 10000 ft AGL. Light winds will prevail.


Issued at 300 AM MST Fri Dec 2 2016

Minimal fire weather concerns will continue through next week as
cold temperatures will remain over the area. Light winds expected
today, but then will be on the increase Saturday as low pressure
begin to approach from the west. Another winter storm system set
to move into the area Monday into Wednesday that may bring
widespread accumulating snow.


WY...High Wind Watch from late tonight through Saturday afternoon for



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