672
FXUS65 KRIW 072154
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
354 PM MDT Mon Apr 7 2025

.KEY MESSAGES...

- Rain and/or snow chances (30-60%) exist across western and
  northern Wyoming late tonight through Wednesday.

- Elevated fire weather conditions are possible Tuesday and
  Wednesday with windy and dry condiditons.

- Warm, near record high temperatures forecast Thursday through
  Saturday.

&&

.UPDATE...
Issued at 148 PM MDT Mon Apr 7 2025

Satellite water vapor imagery (20Z) shows the upper-ridge that
has kept us dry and sunny the past few days, is beginning to
push east and flatten. The forecast remains on track for a broad
trough to push into the Intermountain West region late tonight.
An increase in Pacific moisture into the region, with the aid
of a strengthening upper-level jet, will bring scattered snow
and/or rain chances to western Wyoming late tonight. By mid-day
Tuesday, the nose of a 80-100 knot jet pushes over Wyoming.
This jet combined with 700-mb westerly winds between 20-30
knots will create gusty winds areawide. Precipitation chances
Tuesday will largely be confined to western and northern
Wyoming; however, an isolated light shower outside of these
areas cannot be ruled out. There also remains thunderstorm
potential across northern Wyoming Tuesday afternoon where
instability is greatest due to the area being in the left exit
region of the jet (divergence aloft).

Ensemble guidance remains in consensus that the flow aloft will
go from zonal to more northwesterly on Wednesday as a ridge
begins to build in. As this shift occurs, the upper-jet core
(100-120 knots) will be directly over the state, leading to
another day of gusty conditions. No high wind highlights have
been issued at this time with the threat remaining marginal.
Atonally, with gusty winds and drier air, elevated fire weather
conditions remain possible both Tuesday and Wednesday.

&&

.DISCUSSION...
Issued at 139 AM MDT Mon Apr 7 2025

The axis of the current ridge passes over the state moves through
today. This will bring the warmest temperatures of the next few
days, with highs in the mid-50s to around 60 degrees west of the
Continental Divide (around 50 degrees for western valleys) and mid-
60s to around 70 degrees east of the Divide. A clear sky remains
through the morning, with clouds beginning to move into western
Wyoming mid-day as the next weather system approaches.

Winds begin to increase this morning, notably over the central
mountains (Absarokas and Wind River Ranges) and the Wind Corridor
(roughly Rock Springs through Casper). Afternoon gusts near 30 mph
will be common for these locations, with wind favored areas a bit
higher. Winds decrease some tonight, remaining gusty over the
mountains. Afternoon minimum relative humidities (RH) drop to around
15 to 20 percent, so areas of elevated fire conditions are possible.

A broad trough begins moving into the area late today, flattening
the current ridge over the area. The aforementioned wind is one part
of this system, the other being precipitation. Rain/snow chances
increase across western Wyoming between around 7pm and 9pm MDT. With
the warmer temperatures in place, snow will be limited to the
mountains, though a little snow may mix with rain at times for the
western valleys. Precipitation chances mainly remain over the
western mountains and valleys through Tuesday morning, but chances
spread across northern Wyoming (namely the Bighorn Mountains) later
Tuesday morning and afternoon. Recent high resolution models have
precipitation remaining over the higher elevations (and to a lesser
extent, the western valleys), with 20 to 30 percent chances for the
lower elevations of the Bighorn Basin and Johnson County, with about
15 percent chances around Casper. Precipitation chances linger into
Wednesday, though look more limited to northern Wyoming. There may
be some isolated thunderstorms Tuesday and Wednesday as well.

For wind, Tuesday and Wednesday will be quite gusty. Starting with
Tuesday, widespread gusts over 30 mph occur, in a generally west to
northwest wind. Some locations will have gusts up to around 50 mph,
like the Wind Corridor, or possibly around Cody as winds come off
the Absarokas. Winds trend up for Wednesday as the jet stream moves
over the state. Widespread gusts of about 30 to 50 mph occur, with
favored areas nearing 55 or 60 mph. Will have to watch trends if any
high wind highlights are needed. For now, it`s too marginal to make
a call.

Another ridge follows for Thursday, with much lighter winds compared
to Wednesday. This will also start bringing temperatures up again.
The GFS and ECMWF are in fair agreement of 700mb temperatures
Friday, with 6 to 10 degrees Celsius over the area. Friday continues
to look like the warmest day, though Saturday will be comparable.
Highs Friday are in the 70s for most areas. Long range models are
showing a possible cold front moving in for Sunday, which would
bring cooler temperatures and possible precipitation chances. With
the warmer temperatures, we continue to monitor river levels, though
nothing looks concerning at this time, with river forecasts showing
snowmelt rises, as is usual for spring.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 345 PM MDT Mon Apr 7 2025

VFR conditions for the entirety of the period for all TAF sites
with some mid level ceilings throughout. Some rain/snow shower
activity at KJAC between 05Z-11Z (60-70%) and between 06Z-10Z
(30-40%) at KBPI/KPNA with the next weak wave skirting to the
north of the CWA. VFR conditions should still prevail with lower
ceilings/visibility but staying above the MVFR threshold.
Otherwise, winds will diminish after sunset around 02Z picking
up once again after 16Z at KCPR/KRKS around 25kts spreading to
KRIW/KLND/KCOD/KJAC after 18Z with a stronger gradient than
Monday. Winds up to 30kts at KRKS and 35kts at KCPR after 18Z
remaining through the end of the period before diminishing after
sunset Tuesday evening.

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

&&

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

&&

$$

UPDATE...Gerhardt
DISCUSSION...Wittmann
AVIATION...Lowe