273
FXUS65 KRIW 250350
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
950 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 /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...Myers
AVIATION...Wittmann