Area Forecast Discussion
Issued by NWS Cheyenne, WY

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234
FXUS65 KCYS 182141
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
241 PM MST Wed Jan 18 2017

.SHORT TERM...(This evening through Friday)
Issued at 141 PM MST Wed Jan 18 2017

Tonight...Inherited high wind warning for Bordeaux still in decent
shape. Although wind gusts have remained in the 50 to 57 mph range,
with a peak of 57 mph at 1235 pm, the sustained winds have been
almost consistently from 40 to 45 mph for a handful of hours. With
the Craig to Casper 850 mb height gradient continuing to relax
through early this evening, our 6 pm expiration time looks good for
now.

Tranquil overnight expected with our counties in between systems.
Locally warmer along the I-25 corridor and lee of the Laramie Range
due to low level winds.

Thursday...Despite increasing cloudiness, temperatures will remain
mild with highs from the mid 30s to near 50 degrees at lower
elevations based on projected 700 mb temperatures near 0 Celsius.
Dry weather prevails as the low and mid levels become more moist but
still not enough to support precipitation initiation.

Thursday night...Initial shortwave rotates northeastward across our
western counties ahead of the Great Basin trough aloft, helping to
generate scattered to widespread snows over our western counties and
especially our Snowy and Sierra Madre Ranges where orographics will
combine with dynamics from the shortwave. Dry elsewhere.

Friday...Cooler in the wake of the shortwave and its associated cold
front, though still above normal temperatures for this time in
January. Looks like a lull in snowfall activity due to downward
vertical motion in between shortwaves, though orographic snows will
continue over and near our Snowy and Sierra Madre Ranges with a
slight chance of snow in the Douglas and Converse county areas
with the departing shortwave. Dry elsewhere.

.LONG TERM...(Friday night through next Wednesday)
Issued at 225 PM MST Wed Jan 18 2017

A longwave upper level trough will remain in place through the
long term period resulting in near or slightly cooler than normal
temperatures as well as a few chances for snowfall. Models are
hinting towards a shift in the longwave pattern by late next
week...but there is still the potential for a major snow event
Monday/Tuesday before this pattern shift takes place.

Models still indicate a Pacific shortwave disturbance slowly
moving across east of the forecast area late Friday and Friday
night. Mountain snow showers will linger Friday night as this
disturbance moves east across the central Rockies, then northeast
into the central/northern Plains. Other than a brief period of
snow and rain...not much is expected outside the mountains with
this event. It will turn colder for the weekend...but still near
normal. It will be breezy across southeast Wyoming with gusts
around 45 mph for the wind prone locations along I80 and
I25...especially on Sunday. A shortwave ridge aloft will then
move overhead for Saturday and Sunday ahead of the next Pacific
storm system moving onshore.

For next week...the potential still exists for a significant
winter storm across most of the area. Timing still looks good for
snow to begin on Monday west of I-25...and sometime Monday
night/early Tuesday for the eastern Plains. The new 12Z ECMWF
shows some major differences however...with the storm system
failing to organize as it crosses the central Rockys and
accelerates eastward into the Great Plains. The 12Z GFS still
shows the system developing rapidly across eastern Colorado with
widespread snowfall across all of southeast Wyoming and western
Nebraska. Based on current model data...it appears locations along
and east of I25 will see the highest snowfall rates and snow
accumulation. This might chance over the next few days
though...especially with the ensemble runs showing a wide variety
of possible tracks of the surface low and upper level low. In
fact...all of the ensemble solutions are less progressive and
slower with the upper level low compared to the operational
GFS...which suggests a longer duration of snowfall for the
forecast area. For now...lowered temperatures a bit Tuesday and
Wednesday but made no changes to weather and POP due to the
inconsistent ECMWF.

&&

.AVIATION...(For the 18Z TAFS through Thursday morning)

Other than some patchy fog in the Laramie valley possibly producing
brief periods of MVFR/IFR visibilities for KLAR tonight...expect VFR
to prevail for all terminals today with winds generally below 15
knots.

&&

.FIRE WEATHER...
Issued at 123 PM MST Wed Jan 18 2017

No concerns based on projected winds and humidities.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...High Wind Warning until 6 PM MST this evening for WYZ106.

NE...None.
&&

$$

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



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