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000
FXUS65 KRIW 232336
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
536 PM MDT Tue Apr 23 2024

.KEY MESSAGES...

- A moisture surge will bring some isolated to rain showers and
  an isolated thunderstorm to southern Sweetwater County this
  afternoon.

- Relative humidity remains low today and tomorrow, so elevated
  fire weather conditions continue. Wind will mostly be light,
  so conditions are not expected to exceed elevated levels.

- Rain/thunderstorm chances increase beginning Thursday as
  several weather systems impact the state through this
  weekend.

&&

.DISCUSSION...
Issued at 141 PM MDT Tue Apr 23 2024

Today an upper-low slid well east of the state into the Great Lakes
Region and a dirty ridge has now replaced it. Moist southwesterly
flow is occurring as this ridge slides east and a large upper-low
meanders off the coast of CA. PWAT values will approach 0.5" across
southern portions of the area late this afternoon into tonight. At
the same time a little bit of lift in the form of WAA and some
PVA/CVA will bring chances for isolated to scattered rain
showers/thunderstorms to southern portions of the area. Instability
doesn`t look as impressive this afternoon, so the chance of
lightning has decreased to (15%) for a brief period late this
afternoon. Model soundings show it remaining quite dry in the low-
levels, so strong downdrafts are possible (50%). The majority of the
forecast area will remain dry thanks to that dry air in the low-
levels.

A better chance for rain/thunderstorms exists for Wednesday
afternoon as the upper-low off the coast of CA moves onshore and
begins to impact the area. This will mainly be across
southern/western portions of the forecast area. Elevated fire
weather conditions seem likely for Wednesday afternoon, once again.
Still not looking like wind criteria will be met in critical fuel
zones for Red Flag Warnings, so no plans on issuing a Fire Weather
Watch at this time. Wednesday looks to be the warmest day, with
highs in the low to middle 70s east of the Continental Divide and
low 60s to low 70s west of the Continental Divide.

Thursday into this weekend is looking very unsettled with a large
trough and several upper-lows/shortwaves with plenty of lift and
moisture. The finer details still need to be hammered out at this
time, because it looks like a messy pattern. With model forecasted
PWAT`s of 0.4-0.7" and plentiful lift there will be good rainfall
amounts for portions of the forecast area. The axis of heaviest
rainfall/greatest QPF keeps shifting as model guidance tries to
resolve the timing, location, and interaction among the systems.
This looks like a longer duration more stratiform rain event, so
flooding concerns are low at this time. Not a ton of cold air with
this trough, especially with the first shortwave, so snow will
mostly be confined to elevations above 7500 ft AGL. Certainly can
see substantial snow amounts where p-type is snow with the moisture
that will be available, so the highest elevations of mountain ranges
could see a couple feet of snow. There is potential for minor snow
accumulations across western valleys and the Upper Green River
Basin, but temperatures are very marginal (700 mb temps as low as -4
C Saturday night and surface lows in the upper 20s to low 30s), so
most will melt on contact with surfaces. The active weather pattern
will keep it cool across the area from Friday through this weekend.

The trough slides east Saturday night and most precip is expected to
end early Sunday as a weak ridge tries to develop behind the trough.
This ridge looks short-lived as a jet streak associated with an
upper-low ejects into the state. The strength and location of this
jet streak is uncertain at this time, so impacts range from isolated
showers across western WY to widespread rain showers/thunderstorms
across western WY and isolated rain showers/thunderstorms
elsewhere.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 534 PM MDT Tue Apr 23 2024

VFR conditions through the period with mainly light winds. A weak
shortwave within the westerly flow will bring some isolated showers
to southwestern Wyoming Tuesday afternoon. KRKS is the only station
that could see potential impacts with showers, but they still look
to stay to the south. Only going with VCSH at this time. As the
activity moves to the it will bring increased high clouds will
across the area.

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...Rowe
AVIATION...Swanson/Myers