Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 251751 AAA

Area Forecast Discussion...Update
National Weather Service Riverton WY
1151 AM MDT Thu May 25 2017

.SHORT TERM...Thursday through Saturday night

There certainly were some strong wind gusts yesterday as the front
blew through the area. In addition, thunderstorms developed as the
front sagged southward and interacted with the right rear quadrant
of a jet streak. As of around midnight we still have some
convection but it is slowly weakening as we lose the upper level
support. By morning, there will still be some showers around in
southern areas but nothing heavy is expected.

As for today, it looks much quieter with the front to the south of
the area. With the boundary near the southern border, there will
still be some showers and thunderstorms along the southern border.
In addition, another weak shortwave moving through Montana may
bring a few thunderstorms to the western and northern mountains.
However, coverage will be less than yesterday as a rule. With
cooler temperatures and lower wet bulb zero levels, the main
threat will shift to small hail. In addition, steering flow across
the north will be rather light so most storms should stay in the
mountains. The most noticeable things will be less wind and
cooler temperatures for most people.

Friday at this point looks to be the wettest of the three days
across the area. A mid level area of low pressure is expected to
develop and move across Wyoming. This will likely turn flow to the
northeast and increase upslope across the area. This will lead to
a cool and cloudy day with periods of showers and possibly a
thunderstorm, although heavy amounts of precipitation are not
expected at this time. And yes, it will likely be cold enough for
some of that precipitation to fall as snow in the mountains. This
steadier precipitation should end across the area later Friday

For the start of the Memorial Day weekend, there should some
improvement in the weather. Temperatures should begin a gradual
warming trend with chances of precipitation decreasing. However,
notice how I said decreasing, not ending. With northwest flow across
the area, there will be a chance of mainly afternoon and evening
thunderstorms across the area each day. However, they should be
fairly sparse with most areas dry most of the time. And as it is
with convection, it will be very difficult to pinpoint where the
storms pop up.

.LONG TERM...Sunday through Thursday

A relatively moist northwest flow will be across the area through
Tuesday between an upper ridge over the West Coast/Intermountain
West, and a longwave trough over the central/eastern U.S. Models
show enough moisture and instability with peak heating for daily
showers and thunderstorms forming over the mountains and trying
to push southeast into the basins/valleys. This activity could be
enhanced at times with some subtle waves in the flow and local
convergence zones. Another concern is for convection to put out
gusty outflows well away from their parent convection which could
cause choppy lakes and reservoirs from distant thunderstorms.

By Wednesday and Thursday, models are generally showing a flat
ridge sliding east across the Northern Rockies as a shortwave
trough/upper low digs off the Pacific Northwest Coast. Still
enough moisture and instability for at least diurnal driven
mountain convection possibly pushing into the lower elevations.

Temperatures are expected to be seasonal early next week becoming
5 to 10 degrees above average by mid-week


.AVIATION...18Z Issuance

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

The last of the area of thunderstorms over extreme southern
Sweetwater County will be exiting the area shortly. An upper level
disturbance will move across the northern Great Basin into SW
Wyoming 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

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 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.



Today will be a much cooler day following the passage of a cold
front. Temperatures will average 15 to 20 degrees cooler for most
areas. Relative humidity will also be higher and remain above
critical levels for all areas. Wind should remain light to moderate
for most areas but could remain gusty in portions of southwestern
Wyoming. Mixing and smoke dispersal will be generally good to very
good. An approaching area of low pressure could bring a wetting rain
to some area Friday with some snow possible in the higher





SHORT TERM...Hattings
LONG TERM...Murrell
FIRE WEATHER...Hattings is the U.S. government's official web portal to all federal, state and local government web resources and services.