Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 202104

Area Forecast Discussion
National Weather Service Cheyenne WY
204 PM MST Sat Jan 20 2018

.SHORT TERM...(This evening through Monday)
Issued at 230 PM MST Sat Jan 20 2018

Currently...Winter headlines look on track this afternoon as water
vapor showing upper low ejecting out of the desert southwest.
Seeing on infrared imagery rapidly cooling cloud tops across
Carbon and western Converse Counties at 1PM. Observations
underneath these cooling cloud tops shows Rawlins and Douglas at
3/4 mile while Saratoga was down to 1/2 mile in moderate snow.

Upper low tracks into south central Colorado this evening with our
CWFA in favorable upper level diffluence to the north of the low.
This is when the heaviest snow should beginning out west,
spreading east through 12Z.

Models appear in very good agreement this evening with track of
low and dynamics. Entire CWFA in broad are of 700mb lift of 6-10
ubars. Strong isentropic lift forecast on the NAM 295 and 300K
pressure surfaces from around 09Z tonight through at least 03Z
Monday (Sunday night). Heaviest snowfall rates look to occur from
12Z through say 00Z tomorrow.

Going to be some wind associated with this system Sunday as GFS
850mb winds increase to 30-35kts out in the Panhandle and 700mb
winds 25-30kts across southeast Wyoming. Should see areas of
blowing snow Sunday. Given the winds are not any stronger than
that, do believe we should stay below Blizzard warning criteria.

Upper low tracks into western Kansas Sunday night into Monday
morning. Perhaps our strongest winds to occur Sunday evening
across the Panhandle as the low exits east. 850mb winds in the
Panhandle up to 35-40kts. But given the snow ending towards mid
evening Sunday, not too concerned with with blizzard conditions
during that time.

Winds begin to ease Monday morning with all snow ending and winds
becoming more northwesterly. Upper ridge begins to build back into
the area Monday afternoon.

.LONG TERM...(Monday night through Friday)
Issued at 439 AM MST Sat Jan 20 2018

Models bring a weak shortwave down the northwesterly flow aloft
late Monday which may kick off some snow showers in the higher
elevations of Carbon and Albany counties, but right now this
system doesn`t look overly significant. We note a modest warm-up
midweek, then another storm system progged to move in from the
west late in the week when we will see our next chance of snow.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1032 AM MST Sat Jan 20 2018

A period of deteriorating and poor aviation conditions upcoming
through this TAF cycle. KRWL has already reported snow, with
lowering CIGS at KCYS. This trend will continue through the rest
of the afternoon, as snow slowly spreads northwest to southeast
across the region. The main adjustments for this issuance was to
delay the onset of the heaviest snow at KCYS and western Nebraska
airfields by 2-5 hours. Otherwise, expect snow to continue
developing and become heavy at times, especially overnight and
Sunday morning. As a result, expect widespread LIFR conditions at
most sites. This storm will also cause mountain obscurations
through the period as well.


Issued at 230 PM MST Sat Jan 20 2018

Widespread heavy snowfall expected through the next 24 to 36
hours. Low pressure tracking across Colorado tonight and Sunday
will bring this widespread snow to everyone in southeast Wyoming
and nebraska Panhandle. Fire weather concerns are going to be
non-existent with this widespread snow pack. Snow ends from
northwest to southeast with the southern Nebraska Panhandle ending
Monday morning.


WY...Winter Storm Warning from 5 PM this afternoon to 6 PM MST Sunday
     for WYZ108-118.

     Winter Storm Warning until 2 PM MST Sunday for WYZ101-102-106-

     Winter Storm Warning from 11 PM this evening to 11 PM MST Sunday
     for WYZ119.

     Winter Storm Warning until 2 PM MST Sunday for WYZ103>105-

NE...Winter Storm Warning from 5 PM this afternoon to 6 PM MST Sunday
     for NEZ002-003-019-095-096.

     Winter Storm Warning from 11 PM this evening to 11 PM MST Sunday
     for NEZ020-021-054-055.



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