Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 251831 AAA
Area Forecast Discussion...uPDATE
National Weather Service Riverton WY
1231 PM MDT WED MAY 25 2016
.Short Term...Monday through Wednesday night
The weather pattern over the next few days remains me of a statement
you see on a laundry tag. The phrase is "Wash, Rinse and Repeat."
Basically, we will be locked into this same cool and unsettled
weather pattern for the next few days. However, just like you use
different water temperatures and detergents for different loads of
clothes, there will be subtle differences each day.
As for today, the coverage of showers and thunderstorms could be a
bit more widespread that yesterday. It could also be an earlier show
for a lot of areas. Temperatures will also be a bit cooler however,
and with more cloud cover for many areas instability may be a bit
more limited. Especially the NAM, which has almost no CAPE. In
addition, jet support is a bit less. As a result, thunderstorms
would be a bit less strong than on Tuesday. There could still be
some small hail or gusty winds though, but that describes almost
every thunderstorm in Wyoming. There could also be some snow at the
higher elevations, but above levels that would be a concern for
Thursday could turn out to be the least active day of the three.
Heights do creep a bit higher and this could put more of a cap on
the atmosphere. In addition, there will be little jet support with
mainly light winds for many areas. This could keep much of the
convection close to the mountains and adjacent foothills with the
light steering winds. We still have at least isolated POPS for all
areas, but our gut feeling is that most areas will remain dry
most of the day.
Friday could turn more active once again as another shortwave rounds
the base of the everlasting western trough. This would like enhance
thunderstorms once again. This time however, the models are
indicating that the best chance of convection would shift east of
the divide for that day. As a result, we dried out portions of the
southwest and increased POPS in the east. Temperatures will remain
below normal through the period.
.Long Term...Saturday through Wednesday
Synopsis...A trough of low pressure over the northwest U.S. will
continue to bring cool and unsettled weather to the area through
the holiday weekend. A cold front will push across the area on
Memorial Day bringing increased coverage of showers and
thunderstorms with a few strong to severe storms possible across
central and eastern Wyoming. This will be followed by a Canadian
cold front on Monday night and Tuesday that may bring several
inches of snow to the northern mountains. Drier and warmer weather
is expected on Wednesday.
Discussion...Medium range models in good overall agreement
through the period. Strong upper high pressure will remain over
Alaska with strong downstream ridging over eastern North America
through the weekend. This will result in a blocking pattern with
upper trough trapped in between over the northwest U.S. A
shortwave will rotate northeast across the northern Rockies on
Saturday bringing scattered showers and thunderstorms across most
of the area with the best coverage across the north. Moderate
instability across northeast Wyoming may result in a few
strong/severe thunderstorms along and east of the Bighorn Range.
A southwest flow between shortwaves is expected to result in less
moisture and instability across the area on Sunday with afternoon
and evening thunderstorm activity expected to be more isolated
across the area. Main upper trough is expected to be shoved across
the area Memorial Day and Tuesday in a rather messy fashion. A significant
chunk of this trough will translate Wyoming on Memorial Day
bringing another round scattered showers and thunderstorms through
the area with some strong to severe thunderstorms possible across
central and eastern Wyoming. This will be followed by a trailing
upper low diving southeast across northern Wyoming Monday night.
Snow levels may lower to near 7500 feet across northern Wyoming
with this system Monday night into Tuesday morning with several
inches of snow possible across Yellowstone National Park,
Beartooth Pass area and the Bighorn range. This system will clear
the area Tuesday night with some ridging and warmer and drier
weather expected on Wednesday.
West of the Continental Divide...KJAC/KRKS/KPNA/KBPI Routes
Another upper level disturbance will is producing scattered to numerous
Showers and thunderstorms that will move east into the area early this afternoon
...lasting through the day before finally decreasing in coverage then clearing
out later this evening. Brief periods of MVFR/IFR ceilings and mountain
obscurations may be experienced with any heavier shower or storm. Yet, another
upper level disturbance will be swinging through the area Thursday resulting
in another round of numerous showers and thunderstorms, with the greatest coverage
of shower activity in the afternoon resulting in local mvfr/ifr ceilings along with
mountain obscurations. Some small hail is likely with any storms that develop
East of the Continental Divide...KCPR/KCOD/KRIW/KWRL/KLND Routes
Scattered showers and thunderstorms are expected this afternoon and will last into the
mid evening period before decreasing in coverage along with skies clearing.
Brief periods of MVFR/IFR and mountain obscurations will be experienced with any
heavier shower or storms. A repeat of mostly scattered afternoon and evening thunderstorms
can be expected by Thursday afternoon as yet another upper level shortwave comes through.
Some small hail is likely with any storms that develop through Thursday.
There will be few fire weather concerns through Thursday. A
persistent trough will keep the chance of showers and
thunderstorms around today, with the most numerous storms in the
afternoon and evening. Snow remains possible in the higher
elevations. Relative humidity will remain above critical levels. A
gusty breeze will continue from the Red Desert through Natrona
County. Mixing and smoke dispersal will generally be good to very
good outside of areas of precipitation.