Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 252026
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
226 PM MDT Thu May 25 2017

.SHORT TERM...(This evening through Sunday)
Issued at 200 PM MDT Thu May 25 2017

Cold front from Montana has moved south into northern Fremont and
northern Natrona county with clouds and light showers, colder air
and northerly winds moving south behind the cold front. An upper
level low pressure storm center moving over western Idaho will
move southeast tonight and Friday enhancing dynamics and lift
over the front with a significant increase in precipitation with
the potential for heavy snow in the Absaroka and Wind River
mountains and the northern Bighorn mountains above 8800 feet.
Isolated thunderstorms will be possible with local heavier
rainfall/ snowfall. The precipitation will continue through Friday
night and then taper off Saturday morning as colder air in
northerly flow aloft moves in. Int the Southern Absaroka and
Winder River mountains above 9000 feet, snowfall of 6 to 12 inches
is possible. Some clouds and lighter showers will linger over the
area through Sunday with the greatest coverage in the mountains.
Temperatures will be cold with little snow melt above 8500 feet.

.LONG TERM...(Sunday night through Thursday)
Issued at 200 PM MDT Thu May 25 2017

From Sunday night through Tuesday we will remain on the back side of
the main trough under a dirty northwest flow. Memorial Day will turn
out to be a fairly nice day except for a few afternoon and evening
thunderstorms. Tuesday the coverage of late day thunderstorms will
increase as lifted indices drop to minus 6 in some areas ahead of a
glancing weak backdoor frontal boundary ahead of a 1022mb sfc high
sliding southeast into the Northern High Plains. There will be less
coverage of storms once you move east of the Wind River and Absaroka
Mountains Tuesday afternoon with the influence of the more stable
air behind the boundary. Any storms that occur over the Big Horn
Mountains could produce some snow or snow and rain above 9500 feet
both Monday and Tuesday evening. The south will not see much in the
way of activity where slightly drier conditions will exist. As the
next ridge tries to build in from the west, the flow will become
more confluent with less convective activity by Wednesday. By mid
week, the Canadian, GFS, and Euro all diverge in the solns for the
speed of the ridge building in from the west. The GFS is the fastest
already placing the ridge axis over us on Wednesday and then under a
southwest flow by next Thursday. The Canadian is the fastest with
the Euro in the middle placing the ridge over us by Thursday so will
go with that soln. Have therefore trended late day pops for late day
t storms down gradually Wednesday through Thursday. Temps will
rebound nicely through the extended with highs in the 60s and 70s at
the lower elevations Monday rising to the 70s and 80s by Wednesday.
The far west could be a little cooler by Thursday as clouds from the
west ride up and over the ridge along with isold storms.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 200 PM MDT Thu May 25 2017

West of the Continental Divide...KBPI/KJAC/KPNA/KRKS Terminals

An upper level disturbance will move across the northern Great Basin
into SW Wyoming for the rest of this afternoon. Scattered showers
and thunderstorms are expected to remain south of KRKS toward the
Utah/Colorado border, moving NE into south central and southeast
Wyoming. Isolated showers will be confined mainly to the mountains
further north this afternoon and evening.  A second upper level
disturbance will bring increasing clouds and showers into Far West
Wyoming early Friday morning with areas of MVFR and lcl IFR
conditions along with mtn obscn. These conditions should persist
through much of the day Friday.

East of the Continental Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

A northerly low level flow and slight instability will result in
increasing cumulus and isolated showers and thunderstorms for the
rest of this afternoon into early evening, with most of this
activity in the vicinity of the Continental Divide, vicinity KCOD-
KLND and along the Bighorn Mountains. Showers and isolated
thunderstorms will dissipate around sunset.  Upslope easterly flow
may result in areas of MVFR, local IFR ceilings developing early
Friday morning, vicinity KCPR-KLND. These conditions should persist
through much of the day Friday.

&&

.FIRE WEATHER...
Issued AT 200 PM MDT Thu May 25 2017

Cold front from Montana has moved south into northern Fremont and
northern Natrona county with clouds and light showers, colder air
and northerly winds moving south behind the cold front. An upper
level low pressure storm center moving over western Idaho will
move southeast tonight and Friday enhancing dynamics and lift
over the front with a significant increase in precipitation with
the potential for heavy snow in the Absaroka and Wind River
mountains and the northern Bighorn mountains above 8800 feet.
Isolated thunderstorms will be possible with local heavier
rainfall/ snowfall. The precipitation will continue through Friday
night and then taper off Saturday morning as colder air in
northerly flow aloft moves in. Int the Southern Absaroka and
Winder River mountains above 9000 feet, snowfall of 6 to 12 inches
is possible. Some clouds and lighter showers will linger over the
area through Sunday with the greatest coverage in the mountains.
Temperatures will be cold with little snow melt above 8500 feet.
With cold air, low clouds and precipitation mixing heights will be
low with generally poor smoke dispersal through Sunday. Some
windier areas may get enough smoke transport for fair afternoon
dispersal, especially on Sunday.

&&

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

$$

SHORT TERM...Baker
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...Baker


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