Area Forecast Discussion
Issued by NWS Riverton, WY

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505
FXUS65 KRIW 220440
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1040 PM MDT Mon May 21 2018

.SHORT TERM...(This evening through Thursday)
Issued at 119 PM MDT Mon May 21 2018

A Pacific low pressure trough extending south from the Pacific
Northwest into the Great Basin will deepen and continue to move
east spreading moisture and instability across the area producing
scattered showers and isolated thunderstorms with small hail and
gusty winds this evening.  Clouds and precipitation will become
more widespread on Tuesday with areas of heavy rain along and east
of the Continental divide. Temperatures will cool on Tuesday
with elevated relative humidity as precipitation becomes more
widespread on Tuesday.  Showers will continue with decreasing
thunderstorm activity on Wednesday as temperatures continue to
cool.  The heaviest precipitation will be over central, north and
east areas, with the least in the south. Some showers and
thunderstorms will linger over the area on Thursday with some
warming.

.LONG TERM...(Thursday night through Monday)
Issued at 119 PM MDT Mon May 21 2018

We should see gradually building heights to start the medium range
period beyond our pesky early to midweek upper low which finally
exits stage north later Thursday. There is still some moisture and
instability to start the period Thursday evening for some lingering
convection. Even with warming mid level temps Friday, there is still
some forecast mid level moisture resulting in some building capes
over the far west and possibly far nrn Johnson Friday afternoon. So
some thunderstorm threat in these areas. Otherwise, dry and warm.
The next upper low then begins to enter onto the CA coast Friday
night into Saturday before slowly heading our way over the Memorial
Day weekend. Mean ridge holds to the west so initial feeling is that
system will bump into the ridge and lift more ne across Western WY
late in the Memorial Day weekend or possibly stall out just to our
west which is what the new Euro shows. It initially starts to lift
nnewd on Sunday but then redevelops swd over UT on Memorial Day. The
GFS just stalls it out over UT Sunday through Memorial Day. Either
way, an unsettled period with a high probability of showers and
thunderstorms for much of the area late in the weekend into Memorial
Day. Still a long way off so it will have to be watched closely over
the next couple days. In addition, the warming ahead of this system
with cause rapid snowmelt and if this is followed by more
significant rain, we could see serious river rises on what will be
high water levels to begin with.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1040 PM MDT Mon May 21 2018

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

VFR conditions to prevail into Tuesday afternoon. Expect scattered
SHRA/TSRA to develop at the TAF sites after 20Z with more
predominant TSRA expected toward 01Z, continuing through around
06Z. Local MVFR conditions will occur with some thunderstorms.
Mountains will be obscured at times. Wind gusts to 30 knots and
small hail will occur with stronger storms.

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

Expect showers and thunderstorms to be on the increase Tuesday
afternoon with widespread showers and thunderstorms Tuesday night.
Some storms will be quite strong to severe, especially in the eastern
zones. MVFR ceilings will be predominant at most locations after
02Z.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued AT 119 PM MDT Mon May 21 2018

A Pacific low pressure trough extending south from the Pacific
Northwest into the Great Basin will deepen and continue to move
east spreading moisture and instability across the area producing
scattered showers and isolated thunderstorms with small hail and
gusty winds this evening.  Clouds and precipitation will become
more widespread on Tuesday with areas of heavy rain along and east
of the Continental divide. Temperatures will cool on Tuesday
with elevated relative humidity as precipitation becomes more
widespread on Tuesday.  Showers will continue with decreasing
thunderstorm activity on Wednesday as temperatures continue to
cool.  The heaviest precipitation will be over central, north and
east areas, with the least in the south. Some showers and
thunderstorms will linger over the area on Thursday with some
warming. Mixing heights will be favorable even with relatively
light transport winds to produce good or better smoke dispersal
each afternoon through Thursday except in areas receiving heavier
precipitation where poor smoke dispersal will occur.

&&

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

$$

SHORT TERM...Baker
LONG TERM...Skrbac
AVIATION...Troutman
FIRE WEATHER...Baker



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