626
FXUS65 KRIW 301040
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
440 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 /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1055 PM MDT Mon Apr 29 2024

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

A shortwave pinwheeling around an upper-level low to our northwest
will move east of the Continental Divide early in the forecast
period. Rain showers linger longest in the vicinity of KRKS, but
those will come to an end by 08Z/Tuesday. Other than some
intermittent MVFR at KRKS and KPNA to begin the period, VFR
conditions prevail through at least 00Z/Wednesday. Jet energy
remains overhead Tuesday with widespread westerly wind 15-25kts
from late morning 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. Mountain tops frequently obscured
over northwest Wyoming after that time.

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

All terminals to be VFR through the forecast period. Shortwave
energy combined with left-exit region jet dynamics will allow for
rain showers and mid-cloud decks to linger in the vicinity of KCPR
until 09Z/Tuesday. Other terminals see decreasing clouds early in
the period as the shortwave exits the region by 12Z/Tuesday.
Westerly jet remains overhead Tuesday producing 15-25kt surface wind
for most terminals during the afternoon. These winds diminish
between 00Z-02Z/Wednesday. Otherwise, only increasing high clouds
through the afternoon and evening ahead of the next shortwave.

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...Jones