Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 192135
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
335 PM MDT Sat Oct 19 2019

.SHORT TERM...(This evening through Sunday)
Issued at 335 PM MDT Sat Oct 19 2019

Forecast remains on track for widespread high wind event and
mountainous heavy snowfall. Biggest changes in this forecast
period are the upgrading of all remaining High Wind Watches to
High Wind Warnings for remaining zones in southeastern Wyoming and
all of the Nebraska Panhandle along with the transition for the
North Laramie Range to a Winter Storm Warning from its preceding
High Wind Warning. This transition was deemed necessary given the
forecasted snowfall amounts of over a foot while providing an effective
hazard messaging given potential impacts.

While the forecast for hazard impacts remain some minor
differences amongst model members still persist with overall track
of the low pressure system and position of center low. Most models
suggest a slight deepening into the northern portions of Niobrara
County while others keep motion progressing into the western
Black Hills. While this difference of under 100 miles may seem
insignificant, the stacked isobars are slightly off meaning the
high wind potential depending upon which model used means either a
shorter or longer lived duration of high winds. In either case,
high winds are expected for wind gusts up to 70 mph possible with
likely travel impacts for those with high profile vehicles and
towing trailers.

Moisture advection and overall QPF blended closer to national
partners at the Weather Prediction Center and given the
northwesterly to northerly flow pattern gives high confidence in
the potential for heavy snow in the mountain ranges of over a foot
of snow. High winds coupled with snowfall even in the valleys and
foothills especially around the Sierra Madre and Snowy Ranges will
see blizzard conditions that will severely limit and delay
travelers including those along Interstate 80 between Elk Mountain
and Arlington. Biggest concern regarding the blizzard warnings
will be the persistent of blizzard criteria given the 2-4 inches
of snow possible being blown around by the +60 mph gusts.

.LONG TERM...(Monday night through Friday)
Issued at 254 AM MDT Sat Oct 19 2019

Tuesday...Significantly warmer as 700 mb temperatures rise to near 0
Celsius with downslope west winds under brisk northwest flow aloft.
Perhaps enough moisture for some mountain showers over the Snowy and
Sierra Madre Ranges, otherwise dry.

Wednesday...A fast moving shortwave trough aloft in the northwest
flow aloft will bring a cold front and a chance for rain and snow
showers to the counties, along with a breezy day.

Thursday...Quite cold under the broad trough aloft and with surface
high pressure settling over our counties. Cyclonic flow aloft and
adequate moisture will help produce a chance of snow showers,
primarily in the morning hours, with lesser precipitation chances in
the afternoon.

Friday...Expect a drying and warming trend in the wake of the
shortwave trough passage, and with surface lee troughing becoming
better established, producing downslope warming winds.

&&

.AVIATION...(For the 18Z TAFS through Sunday morning)
Issued at 1125 AM MDT Sat Oct 19 2019

Expect VFR conditions for most southeast Wyoming terminals and all
western Nebraska terminals through tonight and into early Sunday
morning. The only exception will be KRWL and KLAR, which will likely
have a period of IFR/LIFR conditions and snow/low CIGS sometime
between 00z to 07z this evening once the main cold front rapidly
moves across the area. Most favorable location for some prolonged
IFR conditions will be KRWL and vicinity. Further east, do not
expect much with the initial band of snow/rain due to
developing downslope winds.

The primary concern will, of course, be winds.  Gusty west to
southwest winds are expected today before winds weakening a bit this
evening. Forecast guidance continues to show gusts of 45 to 55 knots
for most locations late tonight and into Sunday morning as winds
shift into the northwest, which will be earlier in the day (12z to
18z) closer to KRWL and KLAR, and after 18z for western Nebraska


&&

.FIRE WEATHER...
Issued at 303 PM MDT Sat Oct 19 2019

Strong low pressure system tracks into the region later this
evening with potent pressure gradients in the trowal region to
produce widespread high winds. Area wind gusts will be in excess
of 60 mph and into the 70 mph range. In addition given the
northwesterly to northerly flow, any available moisture will be
enhanced specifically by topographic uplift along the area
mountains producing snowfall with highest elevations expecting to
see over a foot of snow. Areas of significant blowing snow are
expected creating near-zero visibility and blizzard conditions in
the Saratoga valley and the foothills of the Snowy Range including
Arlington and Elk Mountain. Conditions expected to improve as high
pressure builds in behind on Monday. Remainder of the week to be
near-normal temperatures and drier conditions.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from 3 AM to 6 PM MDT Sunday for WYZ101-102-
     107-108-118-119.

     High Wind Warning from 11 PM this evening to 6 PM MDT Sunday for
     WYZ104>106-109-115>117.

     Winter Storm Warning from 9 PM this evening to noon MDT Monday
     for WYZ103-112-114.

     Blizzard Warning from 11 PM this evening to 6 PM MDT Sunday for
     WYZ110-113.

NE...High Wind Warning from 3 AM to 6 PM MDT Sunday for NEZ002-003-
     019>021-054-055-095-096.

&&

$$

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


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