597
FXUS65 KRIW 250852
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
252 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 of areas will 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 /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 949 PM MDT Fri May 24 2024

Prevailing VFR conditions through about the first half of the
period. Two rounds of showers move through the area over the next 24
hours. The first occurs at the start of the period, with most likely
impacts at KRKS through about 15Z. Models have shifted the best
precipitation chances southward, so KRKS could see very little
precipitation. Have kept prevailing rain in the TAF for now, but
confidence is lower. KCPR has about a 10% chance to see a shower.

The next round comes Saturday late afternoon through the evening.
Showers and thunderstorms are possible with this push of moisture.
High-resolution models have a slightly better grasp on starting
times, but struggle with the speed of the system and how long
precipitation chances linger into the evening and early night. Have
attempted to put average start and end times in the TAFs but would
not be surprised to see timings adjust a few hours in either
direction for future issuances.

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...Wittmann