288
FXUS65 KRIW 242000
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
200 PM MDT Fri May 24 2024

.KEY MESSAGES...

- Dry through the end of the day.

- Unsettled conditions return this evening with showers moving into
  southern Wyoming.

- Widespread showers and thunderstorms expected Saturday.

- Sunday will see lingering showers east of the Divide.

- Warmer and drier Memorial Day through the middle of next week.

&&

.DISCUSSION...
Issued at 156 PM MDT Fri May 24 2024

Transitory ridging has taken over in the wake of yesterday`s system.
This has led to a warmer and drier day across the area, though highs
will still peak about five degrees below normal for this time of
year. Returning southwest flow near the surface will make for a
breezy afternoon for most locations while mixing down drier air that
has moved in aloft. This will lead to a few hours of slightly
elevated fire weather conditions for portions of central and
southern areas where humidity will drop below 20 percent.

The quiet weather will be short-lived as unsettled conditions return
this evening. Pacific moisture will increase with the arrival of a
shortwave within the southwest flow. This should lead to some light
showers overnight, mainly limited to the southern half of the area.
This first wave will be quickly followed by a stronger shortwave
trough that will move into western Wyoming by late morning. This
will bring a reinforcing shot of moisture that will contribute to
fairly widespread convection. Showers and thunderstorms will move
from west to east through the afternoon. Hi-resolution models have
been keying in on southern portions of the CWA for the best
parameters for a few stronger storms by mid-afternoon (CAPE over 500
J/kg and bulk shear 30-45 knots). There is some uncertainty on how
quickly clouds can clear from the first wave there which could
limit instability later on. Otherwise, this system is not very
cold, and high temperatures won`t be too much different than
today. Snow will be limited to the mountains with only light
accumulations. The entire area has a good chance (~60 percent)
of at least a little rain, with the most accumulation along and
west of the Divide (40-60 percent chance of a quarter inch or
more).

Showers will mostly come to an end Saturday evening save for some
lingering activity across northern Wyoming into Sunday morning due
to another quick shortwave clipping the area. Sunday continues to
trend drier for most locations with Saturday`s wave moving off to
the east. The exception will still be across northern Wyoming, and
especially the Bighorns and the Powder River Basin. These areas will
see another weak wave dipping down from Montana, as well as a better
moisture pool for an additional round of showers in the afternoon.

Memorial Day will be dry as stronger ridging returns to the area.
Temperatures will return to around or a few degrees above normal.
Further out, ensemble guidance still favors ridging to persist
through midweek before weakening by the weekend. This would keep
drier conditions and temperatures around or above normal
through much of next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1134 AM MDT Fri May 24 2024

Relatively quiet weather expected through the first 18 hours of the
forecast period. Westerly winds gusting 20 to 25kts will be possible
at most terminals through the afternoon, diminishing by sunset.
Otherwise, VFR conditions prevail at all terminals with only FEW to
SCT mid- and high-clouds through the evening hours. Cloud cover
begins to increase overnight, especially west of the Divide as the
next shortwave pushes into the region. Models indicate two separate
waves of moisture with this system. The first, looks to impact KRKS
overnight, between 09Z and 14Z Saturday. Have kept VFR for now, but
occasional MVFR conditions are certainly possible (30% chance)
during heavier showers. There is also a 20% chance of showers
reaching KLND, KRIW, and KCPR with this wave, but have left any
shower mentions out of the TAF due to low confidence. With the
second wave, hi- res models are struggling to resolve exact
timing, but for now, no impacts are expected before the end of
the TAF period.

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...Myers
AVIATION...Hensley