Area Forecast Discussion
Issued by NWS Cheyenne, WY

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972
FXUS65 KCYS 210517
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1017 PM MST Mon Feb 20 2017

.UPDATE...
Issued at 308 PM MST Mon Feb 20 2017

Based on wind gust reports, we have decided to move up the timing
of the high wind warning to now for the Southern Laramie Range,
the I-80 Summit between Laramie and Cheyenne and nearby foothills.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 203 PM MST Mon Feb 20 2017

Tonight...Wind gusts already nearing 50 mph near Arlington and
Bordeaux as the gradient strengthens. Models indicate the low and
mid level height gradients strengthening as evidenced by the 850 mb
and 700 mb Craig to Casper height gradients and 700 mb winds
progged. Subsidence also showing healthy trends, thus it appears
that high winds again will be likely beginning late this evening
over the I-80 Summit and nearby foothills, as well as over much of
the lower elevations east of a Douglas to Laramie line late tonight,
so we have upgraded high wind watches to high wind warnings. Perhaps
some mid level moisture producing a chance of late night snow over
the Sierra Madre Range late. Relatively mild overnight due to winds
and cloud cover.

Tuesday...Strong low and mid level gradients along with winds at mid
levels and subsidence suggests high winds continuing across much of
southeast Wyoming through the afternoon. Somewhat fortunately,
strong downslope warming and progged thicknesses suggest mild
temperatures well into the 60s to mid 70s east of I-25.

Tuesday night...Next progressive shortwave trough aloft and its
associated cold front enters our counties in the evening with
widespread snows developing over and near the Snowy and Sierra Madre
Ranges, with a chance of snow elsewhere at lower elevations west of
a Douglas to Laramie line. Downsloping will severely limit snow
chances along and east of I-25.

Wednesday...Chances for snow will decrease west of a Douglas to
Laramie line during the day as the depth of low and mid level
moisture decreases. Continued windy and colder in the wake of the
cold front with progged low and mid level gradients and forecasted
700 mb temperatures and thicknesses.

.LONG TERM...(Wednesday night through Sunday)
Issued at 203 PM MST Mon Feb 20 2017

Main forecast concern in the extended period is the storm system
that the models show impacting the region from late Wednesday
night through Thursday night. The GFS/ECMWF are in rather good
agreement showing a potent shortwave digging into eastern UT by
12Z Thurs with excellent QG ascent spreading over the CWA,
especially in areas along the Colorado border. Good midlvl
frontogenesis and elevated instability is also depicted in areas
near Interstate 80. With the models continuing to target our CWA
with the best forcing from this system, have widespread likely
pops from Thursday morning through the evening. Went ahead and
issued an SPS, highlighting the upcoming winter weather
conditions. Strong winds, and thus blowing snow, do not appear to
be a major concern with this system with gusts mostly below 30
mph. It will begin to dry out by Friday afternoon, however a cold
airmass will remain in place through the weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1014 PM MST Mon Feb 20 2017

VFR conditions with strong winds developing overnight into Tuesday
across southeast Wyoming and Nebraska Panhandle.

&&

.FIRE WEATHER...
Issued at 203 PM MST Mon Feb 20 2017

Minimal concerns based on projected humidities the next several
days, along with expected precipitation on Thursday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning until 6 PM MST Tuesday for WYZ106-110-116-117.

     High Wind Warning from 4 AM to 6 PM MST Tuesday for WYZ101-102-
     105-107-108-115-118-119.

NE...None.
&&

$$

UPDATE...RUBIN
SHORT TERM...RUBIN
LONG TERM...ZF
AVIATION...GCC
FIRE WEATHER...RUBIN



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