Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 250336
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
836 PM MST Fri Feb 24 2017

.UPDATE...
Issued at 836 PM MST Fri Feb 24 2017

The recent snowfall will provide plentiful moisture and with very
cold temperatures tonight, freezing fog will develop across the
North Platte River Valley. Freezing fog has already begun to
develop at Alliance bringing visibility down to 1/2 mile. Based
on the latest hrrr guidance fog for the rest of the North Platte
River Valley beginning around 6Z. All areas will begin to
dissipate by 12Z tomorrow morning.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 243 PM MST Fri Feb 24 2017

Forecast concerns in the short term deal with winds and blowing
snow.

Currently...Still getting some wrap around moisture from the storm
system that moved through the area yesterday and last night.
Light snow echoes being observed on radar mainly east of the
Laramie Range. Aerial coverage is shrinking, so do not think we
will have any more concerns with snow this afternoon. Allowed all
headlines to expire from the winter storm at 11AM today.

Attention turns to tonight as westerly winds return. GFS 700mb
winds increase to 30kts by 06Z and over 40kts by 12Z Saturday
morning. Local high wind guidance showing Craig to Casper
850/700mb height gradients increasing to the mid 40s after 06Z
tonight. WRKGHT guidance slightly higher with close to 50mtrs.
Lots of loose snow out there across the wind prone areas. Thought
it prudent to issue a Blowing Snow Advisory for the wind prone
areas.

One thing the evening and night crew to keep an eye on is strength
of wind. Did go over guidance on winds for the wind prone areas by
10-15 knots. May need to go higher on the overnight forecast. If
we get much higher, we may need to upgrade the advisories to maybe
a ground blizzard warning for the wind prone areas.

Advisories may need to be expanded Saturday after sunrise as
soundings showing 35kts mixing down at Cheyenne, Laramie and
Rawlins.

.LONG TERM...(Saturday night through Friday)
Issued at 243 PM MST Fri Feb 24 2017

Dry but still chilly Sunday with most locations not going above
freezing except for maybe the southern Nebraska Panhandle for
afternoon highs. We start a gradual warmup Monday as the surface
to midlevel flow goes more west to southwesterly ahead of an
approaching shortwave that will cross the area late Monday into
Tuesday. That next shortwave brings our next chance for snow in
across our western areas Monday into Tuesday, with midlevel winds
40 to 50 kts setting the stage for more mountain snow. If stronger
midlevel winds pan out as some model guidance suggests, we could
see a foot of new snow in the Sierra Madre Range with less than
that in the shadowed Snowies. Although not as windy as what we
are expecting for Saturday, the wind prone areas of SE Wyoming
will see wind gusts 40 to 50 mph just about each day with perhaps
Tuesday into Wednesday being a little stronger.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 508 PM MST Fri Feb 24 2017

Occasional MVFR cigs will continue through sunset, then should
trend up to VFR through the remainder of the evening. One concern
for tonight will be fog formation in the Laramie Valley including
KLAR and river valleys across the panhandle tonight including
KCDR, KBFF and KAIA. Latest high resolution guidance shows fog
developing near these locations, with highest confidence at KBFF
and KAIA. Added mention of either VCFG or prevailing IFR fog at
all four locations during the overnight period. Blowing snow
could then be an issue due to winds 20G35kt tomorrow for
KCYS, KLAR and KRWL, but right now it looks like the stronger
winds won`t mix down until after the boundary layer inversion
breaks around 18Z or shortly thereafter.


&&

.FIRE WEATHER...
Issued at 243 PM MST Fri Feb 24 2017

Widespread snow pack will keep fire weather concerns in check
across southeast Wyoming and Nebraska Panhandle through the
weekend. Cold daytime highs will aid in slow snowmelt, so snowpack
could persist into the middle of next week. No fire weather
concerns expected at least through Wednesday next week.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 5 PM MST Saturday for WYZ106-110-
     116-117.

NE...None.
&&

$$

UPDATE...RJM
SHORT TERM...GCC
LONG TERM...JG
AVIATION...RJM
FIRE WEATHER...GCC



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