366
FXUS65 KRIW 251732
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1132 AM MDT Sat May 25 2024

.KEY MESSAGES...

- An unsettled start to the holiday weekend with scattered
  showers and isolated thunderstorms spreading from southwest to
  northeast.

- Conditions improve after that, with showers restricted to the
  north and east Sunday.

- After a dry and pleasant Memorial Day, unsettled weather
  returns for midweek. Details on timing of precipitation this
  far out remains uncertain.

&&

.DISCUSSION...
Issued at 250 AM MDT Sat May 25 2024

Long time residents of western and central Wyoming know that
Memorial Day weekend is known for being rather unsettled and wet,
and at times cold with snow. And, portions of this weekend will be
no exception. But there is not all bad news. The good news is that
all areas will have at least one nice and dry day, and many areas
will have two. The bad news is most areas will not have all
three remain dry.

Satellite imagery is showing some moisture moving into the area as I
write this around 2 am. The chance of showers and thunderstorms
today looks to progress from southwest to northeast, with areas with
like Buffalo and Casper seeing it last. As for the strength of
storms, there is some CAPE (Up to 500 J/Lg). However, lifted indices
only top out around minus 2 and there is not a ton of jet support.
Clouds spreading over the area will also limit instability somewhat.
For today, it looks the western and southern portions of the area
will see the most showers and storms today (topping out at around a
3 in 4 chance) with tapering chances further east (dropping to less
than a 1 in 5 chance). Many area East of the Divide may be dry most
of the day. With the cloud cover, temperatures will average slightly
below normal. And yes, in the mountains above 8000 to 8500 feet,
there will probably be some snow, but amounts should remain light
for the most part.

The Pacific system bringing the showers will move across the state
tonight, and the chance of showers will shift more northeastward,
with southern Wyoming drying out. A trailing shortwave will then
brush by northeastern portions of the area. This wave has little
moisture to work with, but does have better upper level support with
a 90 knot jet moving into northern Wyoming. This will bring another
chance of showers and thunderstorms across roughly the northeastern
third of the area, roughly north of a Jackson to Thermopolis to
Casper line.  Areas further south will likely have a dry day. There
will be enough downward momentum from the right front quadrant of
the jet to bring a gusty breeze, the central Wyoming, but nothing
close to high wind is expected. As for chances of showers, they
range from around 2 out of 5 around Buffalo then lessening
southwestward, with higher POPS in the mountains. These showers
should end fairly quickly Sunday evening.

Monday definitely looks like the nicest day of the holiday weekend
as ridging moves over Wyoming and brings a day of sunshine and near
normal temperatures. Uncertainty then increases from later Tuesday
through much of the week. The ridge then shifts east as another
upper level low moves onshore in the Pacific Northwest and moves
eastward. Guidance remains divided on the timing of the shortwaves
and how far south impacts can set in this area. Odds definitely
favor northern Wyoming at this time. But details on timing of the
waves and how far south showers can get remains in flux.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1132 AM MDT Sat May 25 2024

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

A convective line along the western Wyoming border late Saturday
morning will traverse the western terminals between 18Z-
21Z/Saturday, lingering until 23Z in the vicinity of KRKS. Gusty
outflow wind of 20-30kts accompanies the stronger convection. While
there could be brief MVFR conditions, VFR prevails for the most
part. Any persistent showers will fade between 01Z-03Z/Sunday with
the setting sun, and clouds dissipate and rise as shortwave
energy clears the region after 06Z/Sunday. Mid-level cloud deck
of 060-090 prevails much of the night at KJAC. Gusty westerly
wind increases late in the period at the three southwest
terminals in favorable west-northwest flow aloft. KJAC wind
increases to southwest 10-20kts after 16Z/Sunday. Mountain tops
occasionally obscured through 03Z/Sunday.

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

Convective line to the west makes its way east of the Continental
Divide during the afternoon hours, generally between 20Z-23Z in the
lee of the Absaroka and Wind River Ranges. Temperature-dew point
spreads favor 25-35kt outflow gusts, with KRIW the most favored
given expected outflow from the west-northwest. KCPR sees the
remnants of this convection between 01Z-04Z/Sunday as shortwave
energy reaches central Wyoming. Light showers linger in the
vicinity of KCOD into the early morning hours. Otherwise, drier
west-northwest flow envelops the region for Sunday. Westerly
wind does increase late Sunday morning at most terminals.

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

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Hattings
AVIATION...CNJ