782
FXUS65 KRIW 301132
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
532 AM MDT Tue Apr 30 2024

.KEY MESSAGES...

- Elevated to near critical fire weather conditions expected across
  most of central and southern Wyoming this afternoon.

- Showers will be more limited to western and northern Wyoming
  today. Light mountain snow is expected through this evening,
  likely reaching the western valley floors overnight.

- Unsettled and cooler than normal conditions continue through
  the end of the week.

&&

.DISCUSSION...
Issued at 436 AM MDT Tue Apr 30 2024

There are a few showers scattered around eastern portions of the
area early this morning as yesterday`s wave departs. This activity
will mostly wane near sunrise, though Johnson County may see
lingering showers through mid-morning. Upper flow will become more
westerly today as a broad, fairly diffuse trough swings to our
north. This will keep isolated convection limited to northern and
western Wyoming through the afternoon. There is not much moisture to
work with, though, and the majority of the area will remain cooler
and dry. It will also be another windy day as an upper level jet and
tightening west to east surface pressure gradient lead to widespread
gusts of 25 to 35 mph. Additionally, the wind will help/combine with
relative humidity dropping into the teens this afternoon to create
near-critical fire weather conditions across the basins.

Cyclonic flow increases this evening as the trough to our north
becomes more organized and ejects a wave toward Wyoming. This will
help advect in a little more Pacific moisture, leading to additional
showers for the overnight hours. This will be most widespread across
western Wyoming, where snow levels will drop to the valley floors as
reinforcing cooler air arrives. Accordingly, light accumulating
snow is possible across Jackson Hole and Star Valley; the latest
HREF run suggests a 40 to 50 percent chance of at least a quarter
inch overnight.

On Wednesday flow becomes southwesterly as the trough axis begins to
push into the area. Precipitation will become more widespread,
though still focused the most on western Wyoming. Additional light
snow will make it to the western valleys through the day, though
warming temperatures above freezing should limit most impacts.
Otherwise, it will be another windy day, especially along the Wind
Corridor; elevated to near-critical fire weather conditions will
return across most of central and southern areas for the afternoon.

Temperatures will cool further Wednesday night, with 700mb
temperatures reaching around -8C by Thursday morning behind the
trough passage. This will bring snow levels down to the basin
floors; we can`t rule out some light accumulation across lower
elevations east of the Divide Wednesday night through Thursday
morning. However, drier air will be moving in at the same time,
limiting available moisture and keeping QPF light. In fact, much of
the area will likely stay dry.

Unsettled conditions and cooler than normal temperatures appear
likely to continue through the end of the week. The forecast
reflects a messy upper flow pattern, with precipitation chances
spread across the entire area Thursday and Friday. Light snow
chances will continue as well, possibly down to the basins again
during the overnight hours. Further out, guidance currently favors a
warmer and drier weekend as transitory ridging moves in ahead of the
next system.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 532 AM MDT Tue Apr 30 2024

Jet energy remains overhead Tuesday with widespread westerly winds
gusting 20 to 30 kts through about 02Z/Wednesday. The next shortwave
arrives in northwest Wyoming late in the period. KJAC ceilings fall
to BKN040-060 and showers develop over the northwest after 01Z
Wednesday. Hi-res models indicate a period of steadier -SN between
04Z and 09Z Wednesday night, however, have only included -SHSN in
the TAF for now due to low confidence in steady precipitation. If
the steadier period of precipitation does occur, expect to see vsby
reductions to IFR levels at times for KJAC terminal. Across other
terminals only increasing high clouds through the afternoon and
evening ahead of the next shortwave. Mountain tops frequently
obscured over northwest Wyoming after 00Z and especially after 04Z.

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