194
FXUS65 KRIW 200506
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1006 PM MST Wed Nov 19 2025

.KEY MESSAGES...

- Periodic isolated snow showers over portions of western and WY
  are possible (20% chances) tonight into Thursday morning.

- Patchy to areas of fog are possible (20 to 30% chances) across
  many basins and valleys Thursday morning. Greatest chances for
  widespread dense fog will be across western WY valleys (30%
  confidence).

- Temperatures 5 to 10 degrees above normal are expected persist
  through the weekend.

- Chances for colder temperatures and precipitation may return
  to the region for the second half of next week.

&&

.UPDATE...
Issued at 1137 AM MST Wed Nov 19 2025

The forecast remains on track today. Skies will become mostly cloudy
as a shortwave moves through. This will bring some light showers and
snow showers to the west through the afternoon and evening.
Accumulations will remain light (an inch or two across the highest
peaks). Snow levels will decrease through the evening, so there is a
chance that some lower elevation locations such as Jackson and Star
Valley and even Pinedale towards Bondurant could see a light coating
of snow from those snow showers after sunset this evening.

As the shortwave exits, WAA and building high pressure behind it, in
combination with clearing skies, fog chances will exist across
most basin/valley locations that are usually susceptible to fog.
This includes river valleys and basins with unfrozen larger
lakes and reservoirs. This would include the Wind River Basin,
especially near Boysen reservoir, the North Platte River valley,
and even possibly the Bighorn River valley. There is low
confidence (20% chances) for fog development. This is generally
riding on how quickly skies clear tonight behind the shortwave.
Some model depictions hold onto clouds much longer than others.
If skies remain mostly cloudy, fog will be less likely. Western
WY basins and valleys also may see fog development overnight,
especially those that see any shower activity during the
afternoon and early evening. Cloud cover will again be the
primary factor in fog development, but giving western valleys a
30% chance of fog for Thursday morning. Any fog that does
develop, should scatter out with mostly clear skies after 1100L.


Thursday, as the low pushes towards the Four Corners, flow across
east of the Divide locations and southern WY turns easterly.
Moisture getting advected up into the region could result in some
weak shower chances (10 to 20%) Thursday late morning into the
afternoon. Any accumulations will be minimal to none with these
showers. More likely chances (20 to 30%) come overnight, and
especially towards Friday morning. Chances do overall remain low, as
there is not much moisture to work with and the parent low will be
too far south to bring much influence into WY. Something perhaps
worth watching especially for Friday into Saturday would be
persistent low clouds that often come with easterly flow across
portions of Natrona County and Johnson County. Especially with
temperatures remaining above normal, any showers and added low-level
moisture could exacerbate this concern.

&&

.DISCUSSION...
Issued at 137 AM MST Wed Nov 19 2025

Near seasonable temperatures and mainly uneventful weather will
start today and likely persist into the weekend. Temperatures remain
at or slightly above normal today with highs in the low to mid 40s
west of the Divide and low to mid 50s east of the Divide. Much of
the state looks to see quiet conditions with partly to mostly cloudy
skies. The exception to this will across portions of western and
southern WY. A weak shortwave will interact with moisture that is
being funneled into the region by a cutoff low from the southwestern
CONUS. This will lead to periodic showers throughout the day today.
The best chances (20-50%) for showers is expected to be across
western WY with lesser chances (10-30%) for parts of southern WY.
Showers gradually dissipate with coverage lessening by the morning
hours on Thursday. The highest elevation mountain ranges of western
WY may see a light coating or at most an inch or two of fresh
snowfall by this time.

The second half of the week into the weekend will see temperatures
remain near to slightly above seasonable with mostly quiet and dry
weather prevailing. This is due to two upper level lows managing
to navigate their way around the area, which seems to be the
theme of November so far. The cutoff low mentioned earlier
currently is over the southwestern CONUS and will gradually
shift east through the second half of the week. This shift looks
to quicken due to another low digging south from the PACNW and
replacing the first low leading to it stagnating over the same
area by Thursday into Friday. The first low is ejected to the
east remaining well to the south of the state to see any
widespread or noteworthy impacts. At most a few showers may be
possible over southern WY (10-30%) late Thursday night into
Friday. The weekend currently looks quiet as the second low
settles in over the southwestern CONUS and zonal flow developing
over the area. The second low will gradually shift east through
the weekend, once again remaining well to the south to see any
impacts here.

Looking ahead to the start of next week, the jet stream is expected
to become active again. This translates to the possibility of
multiple rounds of disturbances moving into and through the region.
However, similar to this week the track and setup will be the key
factors in determining if the state may see any impacts. Along with
the possibility for precipitation there may be a strong push of
cold arctic air for the second half of the week. Models differ
with the track of this cold air with some keeping the coldest
temperatures to the north and east of the area. Overall, many
locations are still awaiting the first real snowfall of the
season, especially east of the Divide. The late arrival of the
first measurable snowfall (1" or more) is starting to near
record values. One location for example is Lander where as of
November 18th is sitting within the top 10 for latest first
measurable snowfalls. If the close calls with disturbances
continues through next week, its very possible Lander may be
within the top 5 latest dates on a record which goes back to
1891. That being said, there may be some chances for
precipitation late next week and with Thanksgiving next Thursday
it bears monitoring.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 957 PM MST Wed Nov 19 2025

Main update this evening is to add some tempo FG to KBPI/KPNA
late tonight. There`s enough of a signal that the low clouds
currently around those two sites may lower enough to bring lower
vis to the sfc briefly around sunrise. There is also a hint of
similar conditions at KCPR, but with a lack of a good
southeasterly moisture push, confidence in sfc FG remains very
low, so will omit this for tonight. Remaining sites will see
some lower clouds, but any fog will remain away from aerodromes
for tonight. Cloud cover lifts through the morning, with most
sites going SCT or better through the day. Low clouds will move
into KRKS late afternoon, but should remain above VFR limits
through 06Z/21.

&&

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

&&

$$

UPDATE...Hensley
DISCUSSION...Dziewaltowski
AVIATION...Straub