Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 110510
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1010 PM MST Sun Dec 10 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 1219 PM MST Sun Dec 10 2017

High clouds will begin to increase from the northwest as an
Alberta Clipper now tracking southeast across Montana approaches
from the northwest and tracks southeast across the Northern Plains
through Monday, swinging a shortwave trough across the area. This
weather system will only increase the northwest winds somewhat and
will not produce any precip. Only a brief cool down will occur in
any areas that are already mixed. Otherwise, expect a
continuation of a strong temperature inversion in the western and
central basins and valleys through Tuesday. Another round of
valley fog is expected in the far west valleys and around Boysen
Reservoir in northeast Fremont County late tonight and Monday
morning. By Tuesday night and Wednesday, the next well defined but
compact vort max is expected to track southeast across the Northern
Plains, with the GFS bringing it through the fastest on Tuesday
night and the Euro/Canadian swinging it through 12Z Wed and a bit
stronger. Nevertheless, it will only enhance the nw winds. Then
the next shortwave will follow quickly afterward which will
produce spotty light precip in the northern mtns late Wednesday
along with a gradually increasing gradient and nw wind as we begin
to transition to a more progressive flow as the high along the
Pacific Coast begins to get pinched off.

.LONG TERM...(Wednesday night through Sunday)
Issued at 1219 PM MST Sun Dec 10 2017

Major pattern change is still shaping up towards the second
half/end of the medium range period and beyond as strong wrn NA
ridge flattens and transitions to strong nw flow (trending
cyclonic early next week as ridge redevelops in the ern Pacific).
Shortwave coming down the front side of the ridge into Wednesday
evening may be strong enough for a few flurries/very light snow in
the nrn mtns but that`s about it. Otherwise, still dealing with
the ridge through Thursday before it starts to flatten.
Strong/high wind event is still shaping up for the Cody Foothills
Thursday night into Friday with winds increasing across the lee of
most mtn ranges and the wind corridor. First significant
shortwave to impact the area as the ridge flattens is Friday
night/early Saturday. The models differ slightly on where this
system originates from (Kamchatka region or Bering Sea) but they
both show it blasting through around Friday night with a shot of
snow out west and a chance of snow east of the divide, especially
north and east. Very strong to high winds will likely develop as
this system moves east of the divide. Snow never really ends out
west as upglide/warm advection quickly develops by Saturday night
in advance of our Sunday system. Strong wnw/nw flow develops with
potential for significant snow out west later Saturday night
through Sunday night along with strong wind. Strong to high winds
in many areas east of the divide, especially lee of the mtns, wind
corridor and Sweetwater Count, Cody Foothills and Dubois to
Riverton area. The quiet weather will be coming to a screeching
halt later in the week and beyond for our forecast area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday)
Issued at 1000 PM MST Sun Dec 10 2017

VFR conditions will prevail through Monday night. Patchy fog or low
clouds are possible once again in the far west valleys and
Yellowstone National Park area through Monday morning.

&&

.FIRE WEATHER...
Issued AT 1219 PM MST Sun Dec 10 2017

Expect patchy freezing fog in the far west valleys and perhaps
vcnty of Boysen Reservoir in Northeast Fremont County late tonight
and Monday morning. A temperature inversion will remain in place
for most locations across the forecast area. Winds will be
relatively light for much of the area except for Natrona and
southern Fremont Counties as well as along portions of the
foothills east of the Continental Divide, which could see winds
gusting out of the west and southwest 20 to 30 mph...causing some
brief elevated fire conditions during the remainder of this
afternoon. Tonight/Monday morning, a dry cold front will cause
some gusty winds over the Bighorns and portions of northern/eastern
Johnson County.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Lipson
LONG TERM...Skrbac
AVIATION...Skrbac/AR
FIRE WEATHER...Lipson



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