112
FXUS65 KRIW 111011
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
411 AM MDT Sat Oct 11 2025

.KEY MESSAGES...

- Widespread rain showers and isolated thunderstorms today,
  primarily along and west of the Divide. Periods of heavy
  rainfall could bring locally heavy rain and possible localized
  flash flooding (up to 15% chance) across western and
  northwestern Wyoming.

- Snow levels over the west will be dropping from 10000 ft to
  6000 ft through the evening as a cold front moves through.
  This could result in a wet slushy snow in the Jackson and Star
  Valleys before midnight.

- Winds will be increasing as the cold front progresses eastward
  tonight. Expect gusts of 35 to 50 mph across much of the area.
  Locally higher gusts to 60 mph will be possible in wind prone
  locations.

- Temperatures 15 to 20 degrees colder Sunday with isolated
  precipitation chances (30%) along and west of the Divide,
  mainly in the morning.

- Sub freezing temperatures Sunday night/Morning morning, with
  widespread readings in the 20s. The western valleys and Upper
  Green River Basin will drop into the teens to near 20 degrees.

&&

.DISCUSSION...
Issued at 133 AM MDT Sat Oct 11 2025

Relatively quiet across the CWA as of 05Z, with most of clouds from
earlier Friday streaming further east over southeastern portions of
the state and the Central Plains. Additional clouds/moisture
associated with the remnants of Hurricane Priscilla are currently
over UT and are expected to reach far southern portions of the
forecast area by 13Z. Showers and embedded thunderstorms will
continue to move toward the northeast through the rest of the
morning and into the afternoon. Locally heavy rain will be the main
threat as PWATs with this airmass will be up to 0.9". For reference,
0.68" is the max values and 0.51" is in the 90th percentile.
Obviously, this is well above normal for this time of year. These
showers will continue to move to the northeast through the afternoon
and exit/end over Johnson County by late afternoon. The second area
of focus will be over western portions, as a storm system approaches
the area. Showers will begin to develop over these areas by 15Z,
with a 50-80% for showers and thunderstorms expected after 18Z.
These storms will be a bit stronger as they will be more dynamically-
driven, due to the proximity of the cold front over eastern ID and
the right exit region of the PFJ. Additionally, CAPE values of 200-
600 J/kg and LI`s around minus 2 will be in place. Even though PWATs
will be around 0.50" in this area due to the more Pacific origin of
the moisture, locally heavy rain and possible localized flash
flooding will be the main threats. Small hail also cannot be ruled
out. These showers and storms will move over areas near Cody and
Rock Springs late in the afternoon. Precipitation will begin to fill
in across the west after sunset this evening, while at the same time
showers and embedded thunderstorms ahead of the cold front move over
the central basins. Snow levels will be quickly dropping over the
western mountains during this time, from 10,000/11,000 ft to about
6000 ft by midnight. Travelers over Togwotee, Teton and Salt Passes
should be prepared for rain changing over to snow early in the
evening. This trend is expected between 03Z and 06Z (9pm to
midnight) in the Jackson and Star Valleys.

The focus will shift to wind tonight, as most of the precipitation
will be exiting/ending across the CWA after 06Z. The cold front will
quickly make its way from one end of the forecast area to the other
(west to east) between 00Z and 12Z Sunday. As such, the strength of
the front and the tightening of the sfc pressure gradient will lead
to gusts of 35 to 50 mph to occur with the passage of the cold
front. Wind prone locations like Clark and Hwy 258 on the south side
of Casper could have gusts up to 60 mph. The focus for these winds
will shift to the east slopes of the Absaroka and Wind River
Mountains, the Bighorns, as well as areas from Jeffrey City to
southern Johnson County Sunday morning. Gusts up to 45 mph will be
common in these areas, with locally higher gusts up to 55 mph
possible. These winds will gradually decrease Sunday afternoon, as
the main storm system moves over western ND. Any precipitation
Sunday will be confined to the northern mountains and Yellowstone,
with chances decreasing through the afternoon. Cold conditions will
be in place Sunday night in the wake of this storm, with widespread
readings in the 20s and the colder spots west of the Divide dropping
into the teens. A Freeze Watch will be issued for eastern portions
of the Bighorn Basin and northern Johnson County as a result.

Dry conditions will be in place Sunday night into Monday as a ridge
builds over the region. This will be irt a strong closed upper low
from British Columbia digging south just off the West Coast. This
will lead to increased southerly/southwesterly flow across the
Cowboy State and gusty winds across the Wind Corridor (Rock Springs
to Casper) as well as southern Lincoln County. Chances for showers
will begin to increase across the south Monday night, spreading
northward across areas west of the Divide, as moisture increases
across the area once again. This trend will continue Tuesday as
the upper low begins to move onshore over northern CA, with
western portions of the CWA having the best chances for
precipitation. Snow levels over the western mountains will rise
to 8500 to 9500 ft by this time. Gusty winds will continue over
the Wind Corridor, the southwest flow pattern remains in place.
The storm system will continue to approach the region Wednesday,
with precipitation chances becoming a bit more widespread.
However, western portions will continue to have the better
chances. Forecast confidence begins to drop by Wednesday, mainly
due to timing issues, but expect cooler/wetter conditions
Wednesday through Friday. The confidence in timing could be
applied as early as Monday, as this forecasted system will be
the fourth such storm in as many weeks. Each of these storms had
been forecasted to move over the area too fast, so would expect
the forecast to slow this system down.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 358 AM MDT Sat Oct 11 2025

Multiple rounds of precipitation expected across Wyoming
through around 07Z Sunday. First round should be moving into
the KJAC vicinity around 12Z. These will continue through mid-
morning. Second round moves across southern in the morning and
central Wyoming during around midday and continues into the
afternoon. Main impacts will be to KRKS. The third round of
more convective- style precip moves into western Wyoming around
18Z, with showers and a few thunderstorms continuing at
KJAC/KBPI/KPNA for most of the afternoon and then spreads north
and east into the evening hours. This line looks to break
quickly around 06Z/12 as the best forcing moves away, so
precipitation will not continue the rest of the night, and is
not expected to reach KCPR. Mainly dry conditions are expected
after this. Patchy fog may develop after 06Z, especially in the
western TAF sites where more substantial rain should fall but
not enough confidence to include in the forecast at this time.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Freeze Watch from late Sunday night through Monday morning for
WYZ004-006-010.

&&

$$

DISCUSSION...LaVoie
AVIATION...Hattings