Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 151206
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
506 AM MST Fri Dec 15 2017

.SHORT TERM...(Today - Sunday)
Issued at 312 AM MST Fri Dec 15 2017

Today...Wind speeds slowly increasing in our wind prone locations,
where a High Wind Warning is in effect. Boundary layer wind
forecast, as well as the Craig to Casper 850 mb gradients near or
over 60 meters today suggest winds should continue to slowly
increase today, thus will continue the warning.

Quite a drastic warming trend today as the flow aloft backs to
northwest and heights and thicknesses increase significantly. 700 mb
temperatures near 4 Celsius will yield maximum temperatures in the
mid 40s west of I-25, with primarily 50s east of I-25.

Tonight...The flow aloft continues to back to west as the next
shortwave trough aloft approaches from the Pacific Northwest,
helping to produce a more mild night with a moderating airmass and
downslope westerly winds, producing a relatively mild overnight
along I-25 from Wheatland to Cheyenne along the eastern slopes of
the Laramie Range.

Saturday...Shortwave trough aloft digs across Utah helping to
produce surface upslope north and northeast winds across our
counties, and producing a colder day with increasing cloud cover
from north to south. NAM is now slower in advancing the
precipitation shield to the south with best chances for afternoon
snow north of a Rawlins to Lusk line where deeper moisture will
exist with frontal lifting.

Saturday night...Energy with the upper trough splits with an upper
low cutting off over Arizona and the northern trough over eastern
Montana and northern Wyoming. Still though, with adequate low and
mid level moisture and the passing cold front, will see at least
scattered snow showers over our counties, though with minimal
accumulations.

Sunday...Decreasing snow chances during the day as the atmosphere
begins to dry out, and upward vertical motion ends. Continued cold,
however, since 700 mb temperatures will only reach near -7 Celsius,
yielding maximum temperatures in the 30s.

.LONG TERM...(Sunday Night - Thursday)
Issued at 312 AM MST Fri Dec 15 2017

A slightly warmer and drier weather pattern is expected to develop
into early next week. The GFS/ECMWF are in good agreement w/strong
WNW flow aloft on the southern fringe of a strong mid level short-
wave/clipper tracking across the Northern Plains Mon-Wed. Pressure
falls to the north should support strong low-lvl gradients and the
potential for high winds in the typical wind corridors. Low chance
for any precipitation early in the period with the bulk of any mid
level energy well to the north of the CWA. Snow chances increasing
Wed-Thu with a cold fropa associated w/a rather strong disturbance
digging into the Great Basin mid-week. Current guidance suggests a
fast-moving/progressive system with limited snow amounts. However,
both the GFS/ECM hint at a low closing off over the 4 Corners late
in the week. If this does occur, any notable differences in timing
or location could significantly impact sensible weather across the
CWA. We will need to closely monitor this system over the next few
days as it has at least a small potential to impact holiday travel
across the region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 500 AM MST Fri Dec 15 2017

VFR prevails through the TAF period. SCT-BKN cloud cover at 15k to
20k feet AGL can be expected today, becoming BKN-OVC around 10k ft
by 06z Saturday. Windy conditions will occur over the southeastern
Wyoming terminals today through about 01z with common gusts of 30-
40 knots along with moderate mountain-wave turbulence.

&&

.FIRE WEATHER...
Issued at 312 AM MST Fri Dec 15 2017

Minimal concerns, except for relatively low humidities this
afternoon from 15 to 20 percent across far southeast Wyoming and
the southern half of the Nebraska panhandle.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning until 9 PM MST this evening for WYZ106-110-116-
     117.

NE...None.
&&

$$

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



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