Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 081159
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
459 AM MST Thu Dec 8 2016

.SHORT TERM...(Today through Friday night)
Issued at 457 AM MST Thu Dec 8 2016

Brutally cold temperatures and wind chills are widespread across
the forecast area early this morning. Most sfc observation
stations are reading below zero temperatures, with the coldest
temperatures so far (as of 4am) Laramie at minus 21F and Deer
Creek along I-25 at minus 24F. Expect to see these reading drop a
few more degrees as we finish out the morning, with temperatures
today only warming into the teens. Thankfully some sunshine today
might help to somewhat relieve the deep chill in the air.

The deep upper trough will shift east today, with heights and
temperatures aloft rising. A weak disturbance will move across
Wyoming tonight, promoting sfc pressure falls along the spine of
the mountains while sfc high pressure persists in western
Colorado. The sfc pressure gradient will strengthen as a result,
with windy conditions developing over southcentral Wyoming as
this occurs. This pattern isn`t quite ideal to see widespread
strong winds, but WAA aloft could cause trapping of stronger
winds in the gap areas of the north Snowy Range foothills. Gusts
in excess of 55 mph are therefore quite possible as H7 winds are
progged to be 45 to 55 kts, so issued a High Wind Watch for this
area tonight through Friday morning, which includes Arlington and
the I-80 corridor from Elk Mountain to Arlington.

Strong westerly flow combined with increasing moisture from the
west will produce orographic snow over the Snowy and Sierra
Madres, with a few light snow showers perhaps moving off the peak
over the I-80 corridor near Arlington. Therefore, the strong
winds and light snow could make for slippery conditions here late
tonight through Friday morning. The mountains could see moderate
snow at times, with accumulations of 6 to 9 inches or so in this
pattern. Large scale forcing looks to be relatively weak so not
anticipating much more than this. Went ahead with a Winter
Weather Advisory starting this evening and continuing through
early Friday evening for snow and blowing snow. Snow should
diminish later on Friday as winds aloft weaken, but may
not completely taper off as westerly upslope flow will not
completely die off either. With the winds and WAA pattern,
temperatures will steadily rise through the night across the high
country, with highs for Friday back into the 20s and 30s across
the board.

.LONG TERM...(Saturday through Thursday)
Issued at 457 AM MST Thu Dec 8 2016

Persistent zonal jet stream will bisect the lower 48 thru the first
half of next week. Shortwave trofs embedded within this progressive
flow will yield periodic bouts of windy conditions, mountain snows
along with leaving the CWA vulnerable to Canadian cold fronts.
Winds will be the main concern on Saturday. Widespread belt of 50-55
knot 700mb peak during the morning hours, while slowly lessening
during the afternoon. KCAG-KCPR H85/H7 gradients sufficiently exceed
the 60 meter threshold during this time as well. Will likely need a
high wind hilite in time for favored wind prone regions of southeast
WY. These strong westerlies will combine with moisture associated
with embedded shortwave energy to produce mountain snows beginning
as early as late Saturday continuing on thru Sunday. At this point
would expect the need for a low end winter headline for Snowy/Sierra
Madre Ranges. There is some indication that light snow will spread
east onto the plains late Saturday night and on Sunday morning as
well. Have steered snow chances upward some for areas south of the N
Platte River on the SE WY plains. Snow ends late Sunday as the
shortwave trof departs. Aside from perhaps some light orographic
snows, dry conditions are expected Monday. Both the ECMWF/GFS
continue to hint at the next, albeit brief, cold air mass will
arrive Tuesday. Have continued trending forecast highs lower on
Tuesday. These will need to be dropped over the coming days should
model cooling trends continue. Models become out of phase quickly by
the middle of next week as the GFS attempts to amplify the large-
scale pattern. Until confidence increases, have trended Wed-Thu
towards normal temperatures and drying conditions. High temperatures
will generally be in the 20s and 30s for most of the period, with
the exception of teens in areas Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 459 AM MST Thu Dec 8 2016

VFR conditions will prevail through the period with just some
increasing clouds thru the day, especially for southeast Wyoming
terminals. Winds are expected to be less than 10 knots through the
day.

&&

.FIRE WEATHER...
Issued at 447 AM MST Thu Dec 8 2016

Windy conditions will develop across the district this weekend,
with the highest speeds expected in the wind prone areas of
southeast Wyoming. No fire weather concerns are expected though
due to cool temperatures and high humidities.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Wind Chill Advisory until 9 AM MST this morning for WYZ101-102-
     104-106>109-116>119.

     Wind Chill Warning until 9 AM MST this morning for WYZ103-105-
     110-113>115.

     Winter Weather Advisory from 6 PM this evening to 6 PM MST
     Friday for WYZ112-114.

     High Wind Watch from this evening through Friday morning for
     WYZ110.

NE...Wind Chill Advisory until 9 AM MST this morning for NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...RJM
LONG TERM...CAH
AVIATION...CAH
FIRE WEATHER...RJM



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