Area Forecast Discussion
Issued by NWS Cheyenne, WY

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101
FXUS65 KCYS 030528 CCA
AFDCYS

Area Forecast Discussion...Corrected
National Weather Service Cheyenne WY
1025 PM MST Fri Dec 2 2016

.UPDATE...
Issued at 838 PM MST Fri Dec 2 2016

Latest water vapor loop showed the mid/upper shortwave trough
axis from east through south central WY this evening. Lift ahead
of trough across portions of southeast WY was waning, indicative
of diminishing radar reflectivities. HRRR showing similar trend this
evening, with a few snow flurries still possible. Lowered PoPs to 10
percent or less for the remainder of the evening. With light
southerly flow tonight, cannot completely eliminate fog potential
for low lying/valley locations. If it forms, it will be brief as
winds shift to southwest toward morning. High winds still on target
by Saturday morning at Arlington and Bordeaux, so no changes to the
warnings. Lowered temperatures a few degrees for areas east of I-25.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 147 PM MST Fri Dec 2 2016

Light snow showers have been falling from Laramie to Cheyenne
over the past few hours ahead of a weak upper trough that is
positioned across western WY. Still not expecting much
accumulation through the evening as lift is rather weak. Snow will
come to an end by the late evening as subsidence moves into
southeast WY behind the shortwave. The weather concern in the
short term will be the increase in winds by late tonight into
Saturday morning over the wind prone areas of southeast WY. The
850mb CAG-CPR gradient rises to 55-60 meters shortly after sunrise
on Saturday. This looks like a favorable pattern for Bordeaux with
the sfc trough just to the east of the Laramie Range. The office
wind model is giving some high probs of high winds for Bordeaux.
Went ahead and upgraded to a High Wind Warning for Arlington and
Bordeaux, but left the southern Laramie Range out. Confidence was
not high enough to include that zone even though isolated gusts to
50-60 mph will be possible.

It will be a breezy day over much of southeast WY, but winds will
decrease some over the wind prone areas by aftn as the gradient
weakens. Zonal flow aloft will prevail through Sunday. It will be
the warmest on Sunday with highs rising into the 40s to the east
of the Laramie Range. The CAG-CPR gradient will remain around 50
meters, so it will still be windy over Arlington. The precip
threat will remain slim after the snow showers wind down this
evening.

.LONG TERM...(Sunday night through Friday)
Issued at 230 PM MST Fri Dec 2 2016

Confidence remains fairly high that we will be experiencing some
of the coldest temperatures we have seen so far this season by
midweek, confidence remains good that we will see snow over the
mountains late Sunday through Wednesday...but fairly low on
seeing significant snowfall across our eastern areas early to mid
next week. The pressure gradient Sunday night should increase with
strong west to southwesterly winds for areas along and west of
I-25 Sunday night into early Monday ahead of an approaching Arctic
cold front. We have good agreement amongst the 12Z guidance that
we will see that front move quickly southeast across our region
during the day on Monday, with readings dropping into the teens
on the plains and subzero to single digits west of I-25 by Tuesday
morning. Coldest readings by mid-week look to be -10 to zero for
elevations above 6000 ft msl Wednesday morning and single digits
for the lower elevations. Basically, the current forecast doesn`t
have the lower elevations in the eastern areas going above
freezing until Friday. The snowfall forecast is a bit trickier.
The general trend of the models is to have the heavier snow over
Colorado but the ECMWF still depicts more widespread heavier snow
farther north Tuesday into Wednesday across southeastern Wyoming
and the western Nebraska Panhandle while the GFS remains less
robust. Carried higher snow chances in the Snowy and Sierra Madre
Ranges starting Sunday night through Tuesday night with a chance
of snow east along and north of the Colorado border with lesser
chances farther northeast towards the South Dakota border. With
westerly 700 mb winds around 35 kts during the day Monday through
Wednesday, the models are not hitting the mountains as hard
amount-wise with orographic snow production. Our most likely
scenario as we can see it now would be for a few inches to fall
over the Sierra Madre and Snowy Ranges with lesser amounts
eastward. This far out that can change so stay tuned.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday evening)
Issued at 1025 PM MST Fri Dec 2 2016

Low cigs /MVFR-ocnl IFR/ will continue overnight, mainly from LAR to
CYS. There may be brief MVFR cigs at RWL thru 08Z. Elsewhere, VFR
cigs will prevail. Light southerly winds overnight will shift to the
southwest and become breezy after shortly before sunrise Saturday
with gusts 20-30 kt. Higher gusts will be possible between LAR and
RWL, and between CYS and DGW.


&&

.FIRE WEATHER...
Issued at 300 AM MST Fri Dec 2 2016

Minimal fire weather concerns will continue through next week as
cold temperatures will remain over the area. Winds will increase
Saturday as low pressure begin to approach from the west. Another
winter storm system set to move into the area Monday into
Wednesday that may bring widespread accumulating snow.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from 3 AM to 3 PM MST Saturday for WYZ106-110.

NE...None.
&&

$$

UPDATE...MAJ
SHORT TERM...ZF
LONG TERM...JG
AVIATION...MAJ
FIRE WEATHER...GCC/ZF



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