Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 181817
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1117 AM MST Sat Feb 18 2017

.SHORT TERM...(Today through Monday)
Issued at 300 AM MST Sat Feb 18 2017

Areas of mid and high clouds moving towards the CWA early this
morning ahead of an upper trough that is digging off the
California/Baja coast. A weak impulse moving northeast ahead of
this system may bring a few showers to the higher mtns mainly this
morning otherwise a mild day across the CWA today with varying
amounts of mid/high clouds. The upper trough will begin lifting
northeast later tonight and Sunday with another impulse bringing a
few showers once again mainly to the higher mtns this evening.
Continued mild on Sunday with mainly dry conditions. The main
upper trough will then pass by the area Sunday evening bringing
more widespread rain and snow with snow mainly confined to the
mtns with not much cold air associated with this system. Could be
a period of rather gusty winds over far southeast Wyoming later
Sunday night as a surface low moves out of eastern Colorado into
Nebraska but wind direction not really favorable for high winds.
Monday looking dry and seasonably cool.

.LONG TERM...(Monday night through Friday)
Issued at 335 AM MST Sat Feb 18 2017

Main forecast concern in the extended will be a potential winter
storm for Thursday and Friday of next week. Before that...models
in good agreement for the early and middle portion of the work
week...showing Pacific energy beginning to impact central Wyoming
as early as Tuesday. The main storm system will still be out in
the eastern Pacific on Wednesday so do not expect any major
impacts until Thursday at the earliest. Models show a strong jet
stream stretching from California northeast towards Wyoming and
Montana. This jet will split into two pieces Tuesday and Wednesday
as it translates eastward...with the northern jet across central
Wyoming and the southern branch further south into New Mexico and
Colorado. The southern branch of the jet will be a key player in
the potential late week storm system. Expect mountain snow showers
Tuesday and Wednesday...with some activity moving into the high
valleys and eastern plains in the form of light rain. The colder
air will not push into central Wyoming until early Thursday
morning...so precip should be mostly rain below 7500 feet. The
only other concern for early/mid next week will be potential
strong winds across the wind prone areas late Monday/early Tuesday
morning. High wind headlines are possible...but should be
confined to the wind prone areas with breezy conditions elsewhere.

Models show the Pacific cold front moving across the area
Wednesday night and then stall somewhere across the forecast area.
An upper level trough will finally push inland and dig southeast
near the four corners region by early Thursday morning. The
position of the front and how far south the trough digs will be
key for potential cyclogenesis Thursday and Friday. Even without
rapid cyclogenesis across the high plains...models indicate strong
frontogenesis near the mountains as well. At this time...all
models show some potential of at least light to moderate snow
accumulations across most of the area through late Thursday night.
Can not get too specific with the details at this time due to
model disagreement with the evolution and movement...but it will
definitely turn colder late next week along with a good potential
for snowfall. Increased POP with values between 50 to 80 percent
on Thursday which looks like the most favorable time period to see
widespread precipitation due to the vicinity of the front along
with llvl instability. There is potential for heavy snow along and
east of the Interstate 25 corridor...but the exact position of
this area of heavier snow is uncertain at this time. Temperatures
will be 20 to 30 degrees colder Thursday and Friday with highs
struggling to reach 30 degrees during the day.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1115 AM MST Sat Feb 18 2017

Wyoming TAFS...VFR, except at Rawlins where MVFR occurs from
09Z to 15Z. Winds gusting 20 to 30 knots through 01Z, then from
23 to 25 knots after 15Z Sunday.

Nebraska TAFS...VFR. Winds gusting 20 to 27 knots through 01Z,
then again to 20 knots after 15Z Sunday.

&&

.FIRE WEATHER...
Issued at 300 AM MST Sat Feb 18 2017

Fire weather concerns expected to remain low into early next week
with mild temperatures and some precipitation. There will be
periods of gusty winds around the mountains...mainly Sunday night
through Tuesday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

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


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