Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 280912
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
312 AM MDT SUN AUG 28 2016

.SHORT TERM...Today through Tuesday night

...Critical fire weather and Red Flag Warnings today across
northwest WY...

Imagery shows relatively flay trof across the northern half of the
CONUS...deeper trof with center over AZ over the south with broad
high pressure from the mid Atlantic eastward. SFC has weak high
pressure across the desert SW, Great Basin and into the Rockies
with a weak trof extending from eastern MT through eastern WY and
into eastern CO. No precip across the FA.

Today, the primary focus of the forecast has to do with another day
of marginal near extreme fire danger mainly across northwest WY. As
local Red Flag has been issued for fires in Yellowstone, current Red
Flag from this office matches it well and also includes the Absaroka
mountain chain and southern foothills to the Dubois area. RH values
will lower to around 15 percent over favored areas while west winds
increase to 15 to 20 mph gusting 25 mph for a 3 to 4 hr window this
afternoon. Slight chance for an isolated shower/storm over the
extreme northwestern zones.

Monday through Tuesday night, upper level ridging begins and
continues through the end of the forecast period while the surface
translates from weak high pressure Monday to weak troffing across
western WY by the end of Tuesday. Most lower elevations remain quite
dry through Monday before some moisture increase is felt across the
eastern zones on Tuesday. However, winds look to remain below
critical levels for a Red Flag Warning across zones where RH values
do bottom out below 15 percent. Otherwise, only very isolated
chances for showers/storms will be possible mainly over the higher
mountain terrain.

.LONG TERM...Wednesday through Sunday

Southwest flow aloft Wednesday with some mid level moisture in the
flow. This would lead to some afternoon and evening showers and
thunderstorms over the mountains...then drifting northeast over
the lower elevations. Warm to hot over the area on the last day of
August. Thursday continues a southwest flow aloft and the
potential for some showers and storms in the mountains and the
adjacent lower elevations. Locally breezy in the afternoon and
still warm to hot over the area. Southwest flow Friday through
next Sunday with some model differences with respect to potential
cooling each day. The GFS model is more aggressive with the cooling
while the ECMWF model holds on the warmth Friday, then cooling
Sat/Sun. Have blended the solutions for now and see how things
look in the coming days. Isolated showers/storms for the most part
Fri and Sat, then potentially more activity next Sunday.

&&

.AVIATION.../12Z ISSUANCE/

VFR conditions will occur through the forecast period with
considerable high cloudiness at times with some mid-level
cloudiness. Very isolated convection are possible late this
afternoon and early evening across far northwest Wyoming...mainly
near the Montana border. Winds will be the strongest this morning in
some locations such as KCPR before the gradient relaxes and winds
veer and weaken in the afternoon.

&&

.FIRE WEATHER...

...Critical fire weather and Red Flag Warnings today across
northwest WY...

Fire weather conditions critical across the northwest forecast area
today...including Yellowstone NP and the Absaroka mountains/valleys
south to the Dubois area. Conditions elevated for all other
locations. Warm and dry conditions will allow RH values to drop
quickly again today, ranging from the single digits to lower 20s
(percent) for most locations across the forecast area. However,
winds with the best potential for gusting to 25 mph will lay across
the those same northwest zones...combining with the very dry
conditions and critically dry fuels to give near extreme fire
weather conditions. Elsewhere, while the air mass will also be very
dry, the winds will generally gust just below critical levels or
reach Red Flag conditions for only a short period of time. Dry air
will remain around the forecast area through Tuesday, however winds
will generally blow/gust less than 20 mph over most critically dry
locations.

&&

.RIW Watches/Warnings/Advisories...

Red Flag Warning until 9 PM MDT this evening for WYZ140-286.

&&

$$

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


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