Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 190136

Area Forecast Discussion
National Weather Service Cheyenne WY
736 PM MDT Wed Apr 18 2018

Issued at 731 PM MDT Wed Apr 18 2018

We are becoming more concerned about the potential for Red Flag
conditions tomorrow mainly around Saratoga. This area had a fire
earlier this week, and it looks as if the afternoon humidities
will be quite low with deep mixing anticipated. The models are
showing some mid cloud decks from the disturbance moving in
towards evening which may reduce the wind speeds during the early
evening. For now, we have decided to issue a Fire Weather Watch
for Saratoga for Thursday afternoon.


.SHORT TERM...(This evening through Friday night)
Issued at 220 PM MDT Wed Apr 18 2018

Tonight...Quiet night as a ridge axis aloft moves overhead and into
western Nebraska by dawn.

Thursday...Southwest flow aloft strengthens in advance of the
approaching powerhouse upper low. In response, surface low pressure
strengthens over western Colorado, producing increasing southeast
winds over our counties in the afternoon. The atmosphere still looks
too dry to support any precipitation. Maximum temperatures in the
mid 50s to mid 60s at lower elevations.

Thursday night...Expect isolated to scattered showers to develop,
particularly after midnight, as the upper trough moves into eastern
Utah, and diffluence aloft moves overhead along with a passing
shortwave trough aloft. With the boundary layer saturating, will
likely see areas of fog after midnight where rain does not fall from
Rawlins to Cheyenne to Kimball.

Friday...The upper trough moves into central Colorado with plenty of
low and mid level moisture over our counties, helping to spawn
scattered to numerous coverage of rain, with snow over the higher
mountain peaks. With the high snow levels, mountain snow
accumulations may be less than advisory criteria.  Later shifts will
need to assess this high mountain snowfall potential. Will be a
cool, breezy and wet day with deep upslope east and southeast winds
and plenty of low and mid level moisture available for precipitation.

Friday night...Widespread precipitation will continue, especially
east of a Lusk to Laramie line, and with rain changing over to snow
at most locations, we may need some Winter Weather Advisories to be
issued for the mountains, and possibly over our eastern lower
elevation locations.

.LONG TERM...(Saturday through Wednesday)
Issued at 220 PM MDT Wed Apr 18 2018

Light rain/snow Saturday morning will end during the day as the
upper low continues to move east over the southern plains. Dry and
warmer Sunday as upper ridging shifts across the area. Next upper
trough makes its approach to the CWA Monday and should bring sctd
rain and snow showers. GFS showing its typical fast bias and
leaned more on the slower EC which brings the trough across the
CWA early Tuesday.  Dry and milder weather again for Weds.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 437 PM MDT Wed Apr 18 2018

Surface high pressure will settle over the northern plains tonight
bringing forth light wind speeds over much of the TAF sites. A
strong upper level disturbance is expected to approach western
Colorado by tomorrow evening. The surface high will depart the
region tomorrow, but this disturbance coming from the west will
cause wind speeds to increase over much of the TAF sites again
after 15z tomorrow. However, VFR conditions will be the rule.


Issued at 220 PM MDT Wed Apr 18 2018

Minimal concerns based on expected winds and humidities,
especially Friday and beyond.


WY...Fire Weather Watch Thursday afternoon for WYZ306.



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