Area Forecast Discussion
Issued by NWS Riverton, WY

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826
FXUS65 KRIW 180903
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
203 AM MST Sat Nov 18 2017

.SHORT TERM...(Today through Monday night)
Issued at 200 AM MST Sat Nov 18 2017

Imagery now shows bookend ridges ovr each coast in this still
progressive pattern with a deep trof through the center of the
CONUS. A large flat upper high still sits over MX including the
oceans on each side. The upper trof axis is current cutting through
cntrl/swrn WY pushing a cold front deep into the scntrl Plains while
post frontal high pressure builds across the west. A few lingering
light snow showers and some gusty west/southwest winds over the
usual spots are all that is left of the exiting system.

Today and tonight: Today, the upper levels become nwrly while high
pressure builds west and lee troffing east creates/maintains gusty
west to southwest winds over the usual spots...nrn/cntrl mountains
and foothills (G35-50kts) in addition to the Wind Corridor(25-
40kts). A High Wind Warning exists for zones 3 and 16 (Upper WR
Basin and Cody Foothills) through Tonight.

Sunday will see a similar wind pattern with a better chance for High
Wind conditions across the Absaroka Mountains and Cody Foothills
Sunday night with strong SFC P, T, and Omega Grads under
increasingly favorable mountain wave production aloft ahead of the
next approaching jet/SW trof. Isolated High Wind could also be found
across the Wind Corridor from late Sunday afternoon through the day
Monday. Precip chances will remain out of the FA through Sunday
night before returning across western WY by mid-day Monday. With the
region already under nw flow aloft, another approaching strong jet
(120-150kts) and associated embedded shortwave will start (nearly)
all precip out as snow when it first arrives later Monday morning,
then possibly mix with rain in the valleys in the afternoon. A low
enough dew point depression may keep wet bulb temps low enough to
keep it as all snow. It`ll be fine line. Only modest moisture with
this system as it moves through a ridge to the west. Possible low
end Advisory conditions across a few of the western mountain groups
through Monday night.

.LONG TERM...(Tuesday through Saturday)
Issued at 200 AM MST Sat Nov 18 2017

Tuesday and Wednesday will see NW flow over the area. GFS and
ECMWF models keep moisture in the flow through Wednesday
afternoon. This leads to some snow at times in the Western WY
mountains. Expecting mainly rain at times in the far west valleys
due to the expected high temps. The rest of the region will be dry
with breezy areas in the usual wind prone locations of central WY.
High temps look to remain on the mild side Tue and Wed. Precip in
the west decreases Wed night.

Thanksgiving Day looks dry and very mild for the region. The
models are brining a weather system into the region next Friday
through Saturday morning. The 00Z runs are more bullish with the
prospects of rain and snow. Will have to watch this evolve over
the coming days. Have added a chance of precip to many areas based
on a blended solution. Weather conditions improve next Saturday
afternoon. High temps will be a little cooler Fri and then colder
next Saturday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday)
Issued at 200 AM MST Sat Nov 18 2017

Expect VFR conditions to continue through the forecast period.
Gusty wind will occur at some locations today with the wind
decreasing after 00Z.

&&

.FIRE WEATHER...
Issued AT 200 AM MST Sat Nov 18 2017

Fuels remain at critical levels across over portions of Fremont,
Johnson and Natrona Counties.

Fire weather conditions will be relatively low today below seasonal
temperatures and minimum RH values ranging above 30 percent at all
locations. No precipitation expected today. Winds, however will
remain quite gusty again today...especially across the central/
northern mountains and foothills in addition to eastern Sweetwater
County. Sunday, some enhancement to fire weather conditions can be
expected as temperature warm slightly and the surface/boundary layer
dries out further with afternoon RH values dropping into the upper
teens to mid 20s (percent) east of the Divide and across southern
Wyoming while winds gust out of the southwest 25 to 40 mph at times
across the critical fuel zones (see above).

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

High Wind Warning until 5 AM MST Sunday for WYZ003-016.

&&

$$

SHORT TERM...Braun
LONG TERM...AR
AVIATION...Troutman
FIRE WEATHER...Braun



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