Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 220536
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1036 PM MST Sat Jan 21 2017

.SHORT TERM...(This evening through Monday)
Issued at 250 PM MST Sat Jan 21 2017

Current KCYS radar loop shows bands of light snow moving northeast
across the mountains as an upper level disturbance moves eastward
across the southern Rockys. Current SNOTEL obs not showing much in
the way of accumulation so far...so will not issue any headlines
at this time as snow accumulations will generally remain under 6
inches across the Snowy and Sierra Madre ranges. Kept POP between
60 to 80 percent in the mountains. Would not be surprised if some
of this snow moves into the valleys and eastern plains adjacent to
the Laramie Range. Increased POP up to 20 percent along most of
I80 through Cheyenne for isolated snow shower activity and
flurries.

For tonight...will need to keep an eye on winds for our wind prone
locations with very windy conditions expected...especially around
Bordeaux. However...llvl pressure gradients are below critical
thresholds so will just word forecast for winds between 25 to 35
mph and gusts up to 55 possible through early Sunday morning.
Brief lull in the snowfall activity on Sunday as we will be in
between Pacific systems...with highs in the 40`s east of the
Laramie Range but remaining in the 20`s to near 30 west of the
Laramie Range.

For Sunday night and Monday...attention shifts towards the
Pacific storm system approaching the central Rockys. Models show
high amounts of mountain snow/valley rains for
California...Nevada...and Arizona as the system moves onshore.
Models indicate snow redevelop over the Snowy and Sierra Madre
ranges Sunday night with snow becoming more steady on Monday. The
valleys may start to see some snow by noon Monday as the initial
energy lifts northeast. Do not expect much precipitation for the
high plains through Monday afternoon...so kept POP low along and
east of I25 for now. May need a Winter Storm Watch for the
mountains over the next 24 hours for a prolonged snow event. For
the valleys and east central high plains...there is still quite a
bit of uncertainty with snow amounts but will consider a winter
weather advisory with 2 to 4 inches of snow. This forecast may
change quickly due to the uncertain position of the low pressure
system. As of right now...it looks pretty progressive as it
redevelops east of Wyoming Monday night.

.LONG TERM...(Monday night through Saturday)
Issued at 131 PM MST Sat Jan 21 2017

Monday night/Tuesday...Low level cold front moves south across our
counties with the cold air gradually deepening. Aloft, upper level
diffluence and a shortwave will rotate northward across our
counties. With a moist atmosphere overhead, we expect areal coverage
of snow to increase overnight Monday night with best coverage across
the Snowy and Sierra Madre Ranges and also over the northern Laramie
Range. Best upward vertical motion and lift progged to occur Tuesday
morning with best lift moving into Colorado in the afternoon.
However, looks like enough lift and deep enough moisture to produce
30 to 60 percent POPS.

Wednesday...Will see a drying out period as the flow aloft turns
northwest, though still with orographic snow showers over our Snowy
and Sierra Madre Ranges on somewhat moist mid level flow. Continued
cold with 700 mb temperatures progged to only be near -16 Celsius.

Thursday...Cold air remains entrenched across our counties with
cyclonic northerly flow aloft and progged 700 mb temperatures near
-16 Celsius. Enough low and mid level moisture in the flow aloft
for some snow showers over the Snowy and Sierra Madre Ranges.

Friday...Continued cold with a slow warming trend due to northerly
flow aloft. Breezy to windy day based on progged low and mid level
gradients. Limited low and mid level moisture for a mostly dry day.

Saturday...Slow warming trend continues though temperatures will be
limited by northerly flow aloft, retarding warming. Continued dry
with limited low and mid level moisture.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1031 PM MST Sat Jan 21 2017

MVFR conditions are expected to persist at KRWL through 10z w/snow
showers in the vicinity. Otherwise, VFR prevails w/ ceilings 5k to
10k feet AGL overnight. Expect increasing winds tonight for the WY
terminals with frequent gusts between 20-30 knots. Improvement for
Sunday, but expect lowering ceilings again after 00z with a chance
for snow west of the Laramie Range.

&&

.FIRE WEATHER...
Issued at 204 PM MST Sat Jan 21 2017

No Fire Weather concerns through next week with chilly
temperatures...high relative humidities...and areas of
snow cover. Another round of snow is expected Monday and Tuesday
as another storm system moves across the area.

&&

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

$$

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



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