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000
FXUS65 KRIW 222328
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
528 PM MDT Mon Apr 22 2024

.KEY MESSAGES...

- A passive weather pattern keeps skies mostly clear and mild
  today.It will be very dry this afternoon, so fire weather
  conditions will be elevated.

- A moisture surge will bring some isolated to scattered rain
  showers/thunderstorms to southern WY Tuesday afternoon.

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

&&

.DISCUSSION...
Issued at 134 PM MDT Mon Apr 22 2024

Skies are clear across the area today, which is allowing for
temperatures to warm nicely this afternoon. It will be slightly
cooler than yesterday, today. This is thanks to some colder air
moving in overhead as an upper-low passes to the north. A lack of
moisture and with all the energy to the north of the state means
skies will remain clear, and very dry surface conditions will
continue. Breezy to windy conditions are developing this afternoon
as well, especially from southern Lincoln County through Sweetwater
County. This is leading to elevated fire weather conditions across
the area, especially for the southern half of the state. This will
be discussed more in the fire weather discussion below.

Tomorrow the upper-low will slide well east of the state into the
Great Lakes Region and a dirty ridge will replace it. Moist
southwesterly flow will occur 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 Tuesday. 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 on the order of 500
J/kg of CAPE is likely (80%), so expect lightning to occur Tuesday
afternoon/evening. 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 RH/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, but that could certainly change (RH has been
quite a bit lower today than initially expected). Wednesday/Thursday
look to be the warmest days, with highs in the upper low to middle
70s east of the Continental Divide and 50-60s wet of the 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 0.5-0.7" and plentiful lift there will be good rainfall
amounts for portions of the forecast area. The best moisture is
likely (70%) to be east of the Continental Divide and current
forecasted QPF is on the order of 1-1.5" in the Wind River Basin,
with up to 0.5" west of the Continental Divide (excluding YNP), and
about 0.5-1" elsewhere (including YNP). 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. 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. The active weather pattern will keep it cool across the
area from Friday through this weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 526 PM MDT Mon Apr 22 2024

VFR conditions will continue through the next 24 hours with only
scattered to broken mid and high clouds. Gusty winds, with frequent
gusts above 25kts at the TAF sites will begin to diminish after 02Z.
KJAC will see lesser gusts, but still up to 20kts possible. KRKS is
gusting 35 to 40+ knots. KBPI and KPNA will also see occasional
higher gusts 30 to 35 knots.

Wednesday morning will see another increase in wind speeds as early
as 14Z, but mainly after 20Z. The increased winds won`t be as
widespread with KRKS, KBPI and KPNA seeing the highest gusts, but
only to 20kts or so. Skies will remain partly cloudy in the mid and
high clouds.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued at 134 PM MDT Mon Apr 22 2024

Elevated fire weather conditions are occurring this afternoon as RH
values have dropped/will drop into the low teens across southern
zones. Wind is also gusting 30+ mph in the same areas. RH values
will continue to drop low (15-25%) Tuesday/Wednesday afternoon, but
wind will be lighter, only gusting to 15 mph, Tuesday afternoon, and
20 mph Wednesday afternoon. So, elevated fire weather conditions
will persist through Wednesday afternoon before more moisture moves
into the area on Thursday. Isolated to scattered rain
showers/thunderstorms will develop across southern Sweetwater County
Tuesday afternoon/evening, but little rain accumulation is expected.
Dry lightning is possible (20-30%) in Sweetwater County Tuesday
afternoon/evening. A more widespread chance of isolated rain
showers/thunderstorms is forecasted for Wednesday afternoon, but
chances will remain low (10-30%) for most of the area. Dry lightning
is also possible (20%) Wednesday afternoon. It is looking quite wet
across the area from Friday through this weekend.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Rowe
AVIATION...Swanson/Myers
FIRE WEATHER...Rowe