483
FXUS65 KRIW 301700
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1100 AM MDT Fri Oct 30 2026

.KEY MESSAGES...

- Shower potential increases for areas west and southwest
  Wyoming late this afternoon and overnight. Precipitation (20%
  to 30% chance) pushes into northern and central Wyoming early
  Saturday morning.

- Shower activity is forecast to be more isolated to scattered
  Saturday afternoon and evening, with overall dry conditions
  for trick-or-treating activities!

- A potent weather system reaches western Wyoming early Sunday
  morning and slowly shifts east Sunday afternoon into Monday.
  Most low elevations are expected to see rain whereas snow will
  be confined to the higher elevations.

- Temperatures through Sunday are forecast to be in the upper
  40s to 50s each afternoon. Widespread cooler temperatures
  arrive Monday with highs in the 40s for most.

&&

.DISCUSSION...
Issued at 230 AM MDT Fri Oct 30 2026

It is now October 30th. Where I grew up, in southern New England,
this was know as Mischief Night. This was a night when young people
did mostly harmless pranks, like shaving cream on a car or toilet
paper one someones house or trees. We do have a couple of systems
that will be moving through over the next few days, so it looks like
the weather could cause some mischief as well.

We are dry right now. However, deeper moisture is noted over Nevada
and Utah. And this moisture will ride northeastward, along with a
shortwave that will start to bring some showers. However, today
should be dry for most areas, especially East of the Divide. For
most here, the day looks like a decent one with a mix of clouds and
sun and above normal temperatures. There will be a bit of breeze at
times as well in the wind prone areas from Rock Springs to Casper as
flow will be southwest. Any showers today should be confined to
western Wyoming, but even here chances are generally 1 out of 3 or
less with most locations remaining dry.

The deeper moisture from this wave should arrive tonight into
Saturday and bring a better chance of showers. The main area of
showers will be West of the Divide. Almost all locations East
of the Divide have a 1 in 3 chance or less of a tenth of an inch
of rain from Friday night through the day on Saturday. The only
areas with a greater than 1 in 2 chance of a quarter of an inch
or more are the western mountains. And, with the southwest
flow, this will be a warmer event. The 700 millibar temperatures
are expected to remain at 0 celsius or higher, with the warmest
temperatures further east. This would keep snow levels above
8500 feet with any snow accumulation limited to above 10000 feet
in the western mountains. So, travel problems are not expected
through this timeframe. And there is some good news for trick or
treating or holiday parties. It looks like most of the area
will be in between systems for most of Saturday evening and even
late at night, so most areas should be rain free. There is a
small chance of showers in far western Wyoming but the chance is
less than 1 out of 3 until after around 3 am.

The main show still looks to be from Sunday into Monday, and this is
where some mischief in the weather would most likely be found. The
players remain the same as yesterday, with a longwave trough and
upper level low moving eastward and another low with a feed of
Pacific moisture moving in from the southwest. All in all, reasoning
looks the same as yesterday at this time. The systems are expected
to phase. The heaviest precipitation should remain to the south of
Wyoming. Most of the area, with the exception of portions of the Big
Horn Basin, Wind River Basin and southern Green River Basin have at
least a 1 in 2 chance of a quarter of an inch of precipitation or
more. The greater than 1 in 2 chance of 0.75 inches of liquid is
generally restricted to the mountains. In the lower elevations, the
best chance would be in areas favored by northerly upslope flow,
places like Casper, Lander and south of Worland. Buffalo may also
see more, where there could be wrap around precipitation as the low
moves to the east. Timing is coming more into focus as well. The
steadiest precipitation in western Wyoming looks to be from midday
Sunday through Sunday evening. East of the Divide, the steadiest
would be Sunday night into Monday morning. All precipitation should
end Monday night as the low moves into the Plains States.

The next question is, what about snow and how much? Somewhat cooler
air will move into western Wyoming during the day on Sunday, but
will really spread across the entire area Sunday night into Monday.
At this time, the lower elevations look to be largely rain. The
colder air in most locations doesn`t get deep enough until most of
the moisture is east of the area. Snow levels look to be around 6000
feet by Monday morning. Places like Dubois may see some snow, and
some lower elevations may see some flakes in the air Monday morning,
but accumulation looks slim to none. The western valleys will likely
see some snow, but again, accumulations at this time look like a
coating at the most. The mountains obviously look more interesting.
Most locations above 10000 feet have at least a 1 in 2 chance of 6
inches of snow or more, but the chance of a foot or more is
generally restricted to above 11500 feet. It could get slick over
some of the higher passes though, especially Togwotee and Granite
Passes, and possibly Powder River or Teton Passes. We may need some
advisories for the higher elevations (greater than a 1 in 2 chance).
However, since the main impacts are still more than 48 hours away,
we will hold off for now.

Following this, ridging should build over the area and bring mainly
dry conditions Tuesday and Wednesday. A weak system may bring a few
showers later in the week. However, as of now, no major systems are
expected past Monday for most of the next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1100 AM MDT Fri Oct 30 2026

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals.

High clouds continue to increase today with the approach of the next
weather system. Shower chances will be on the increase after 00Z,
with more confidence in precipitation beginning in the 02Z to 06Z
time frame. Have nudged the timing of the showers forward a bit and
increased likelihood of precip at all sites tonight into Saturday.
Expect a mix of rain and snow later tonight into Saturday morning,
which will draw down some of the visibilities. MVFR ceilings will
accompany precipitation, with KJAC approaching IFR flight conditions
around 10Z, which will continue through most of the morning
Saturday. Frequent mountain obscurations can be expected.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals.

High clouds continue to increase today with the approach of the next
weather system. The greater precipitation chances exist across
western Wyoming, but there is generally a 30 percent chance of rain
showers at most East of the Divide terminals after 08Z Saturday.
MVFR ceilings are forecast to accompany any precipitation. PROB30
groups have been added to reflect the precipitation chances.
Confidence is much lower (around 15 percent) at KCPR, so opted to
not mention in TAF at this time. Mountain obscurations are
possible after 08Z Saturday.

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...Hattings
AVIATION...Straub/Gerhardt