Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 201801
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1201 PM MDT Fri Oct 20 2017

.SHORT TERM...(Today through Saturday night)
Issued at 330 AM MDT Fri Oct 20 2017

Concerns will focus on near-critical fire weather conditions
today, then on winds tonight and especially Saturday night into
Sunday.

One more unseasonably warm day across the CWA today ahead of an
upper trough moving over the northwestern CONUS. Looking pretty
windy out west as a favorable southwesterly mid level flow mixes
down with wind gusts around 50 mph possible in that area. Breezy
over the adjacent high plains of SE WY this afternoon bringing
increased fire danger but it appears humidities will be a little
higher today.

The upper trough will move across the Rockys into the plains
tonight and Saturday. It will push a strong cold front across the
CWA this evening and bring some rain and snow showers to mainly
the mtns aided by orographics. Saturday will be windy and much
cooler with max temperatures about 20-25 degrees cooler along with
healthy northwesterly winds of 20 to 30 mph and gusty. Mainly
clear and mild Saturday night and Sunday but it appears a decent
wind event will develop Saturday evening as lee troughing deepens
over the high plains and a favorable upper jet position allows
for strong winds to reach the surface, especially in the wind-
prone areas of southeast Wyoming where 7H winds increase to around
60 kts. With good downward omega progged over the mtns have opted
to post a high wind watch for the favored areas Saturday night
into Sunday.

.LONG TERM...(Sunday through Thursday)
Issued at 330 AM MDT Fri Oct 20 2017

Strong zonal flow aloft continues through Sunday night as a 140kt
upper jet and associated mid level waves traverse across the
northern Rockies. Pattern becomes a bit more amplified on Monday
into Tuesday as ridging builds along the west coast

Main concern for the long term will be the continuation of very
strong winds for parts of SE Wyoming especially in the wind prone
areas of Arlington, Bordeaux, and the South Laramie Range.  Low
level CAG-CPR gradients through Sunday night remain above 60 meters
and 700mb winds continue to be around 50-55kt.  Should see solid
high wind criteria for the above mentioned wind prone areas through
at least Sunday. Will also likely see strong gusts in Cheyenne on
Sunday as well since forecast soundings indicate 50kt winds as low
as 1000ft AGL on Sunday morning and any mixing at all will allow
strong wind gusts to the surface.  Lapse rates are marginal but
there is some indication of low level subsidence which could help
focus stronger winds closer to the ground.  For now, kept winds
below high wind criteria for Cheyenne and Rawlins but it could be a
close call.

Winds should diminish somewhat on Monday as the pattern becomes more
amplified and a weak surface cold front backs southward through the
plains, turning winds more northerly.  A few weak showers are
possible across the northern counties on Monday as a mid level
disturbance passes to the north along with a strong jet max.  Low
level downslope flow should limit shower chances further south.
Tuesday and Wednesday will begin a warming trend with tightening low
level gradients continuing windy conditions along and west of I-25.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1147 AM MDT Fri Oct 20 2017

Gusty winds will persist across KRWL this afternoon in advance of
a cold front moving through western Wyoming. This front will pack
quite the punch with strong gusty northwest winds developing
behind it. This front should move through KRWL around 02z and
KLAR/KCYS (03Z-04Z), and the Nebraska Panhandle sites between
05z- 07z. Not expecting much in the way of precipitation with this
boundary, due to a very dry boundary layer.


&&

.FIRE WEATHER...
Issued at 330 AM MDT Fri Oct 20 2017

Unseasonably warm for one more day today. Conditions may get
close to critical levels this afternoon over the plains due to
some breezy winds but it appears humidities will stay generally
above critical levels. A strong cold front will sweep across the
districts this evening bringing windy conditions along with much
cooler temperatures for Saturday. Not much precipitation expected
other than a couple inches of snow possible over the higher
mountains tonight. A period of strong winds looks a good bet
around the mountains Sunday night into Monday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from Saturday evening through Sunday afternoon
     for WYZ106-110-116-117.

NE...None.
&&

$$

SHORT TERM...RE
LONG TERM...DEL
AVIATION...REC
FIRE WEATHER...RE



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