576
FXUS65 KRIW 012245
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
345 PM MST Sun Nov 1 2026

.KEY MESSAGES...

- Widespread lower elevation rain and mountain snow occurs
  through Monday. All locations will likely (60% chances or
  greater) see moisture. Minor winter travel impacts for
  mountain passes.

- Gusty winds move in tonight, continuing through Monday
  afternoon as a cold front pushes through from the north.
  Strongest winds occur for the Bighorn Basin and Johnson
  County, where gusts 50 mph or greater are likely.

- Seasonal temperatures with limited precipitation chances
  Tuesday through Friday.

&&

.UPDATE...
Issued at 1132 AM MST Sun Nov 1 2026

Widespread precipitation is ongoing, with an overcast sky and green
returns on radar. Current webcams show snow at the higher
elevations, such as Togwotee Pass. Things seem to be on track.

A couple additional highlights were added this morning. Starting
with snow, a Winter Weather Advisory was added to both the eastern
Wind River Mountains and the eastern Bighorn Mountains. As
confidence has increased with the weather system`s track, upsloping
precipitation is likely to bring snow totals of 6 inches or greater
to these mountain locations. The highest totals occur for the far
northern Bighorn Mountains, at elevations above 9000 feet near Cloud
Peak - totals around a foot. However, mountain passes will see less
snow, so an advisory seems appropriate given the combination of snow
and wind.

For wind, have upgraded to a High Wind Warning for northern
Johnson County for winds 55 to 60 mph tonight and into early Monday
afternoon. Consideration was given to Big Horn County, but
confidence in widespread gusts of 60 mph is not high. Perhaps a gust
may get close with frontal passage. The other consideration was for
the southern half of Johnson County. Strong winds over 55 mph will
likely occur into the middle of the county, but are not expected
further south towards places like Kaycee, so have kept the warning
to just the northern half.

&&

.DISCUSSION...
Issued at 136 AM MDT Sun Nov 1 2026

The weather has cooperated for the most part for evening activities
for Halloween. We are now entering what I call the 151 days (or 152
if it is a leap year) of winter in western and central Wyoming. This
is when we usually start expecting more wintery precipitation than
rain. I say usually because the past couple of winters have been
unusually warm and dry. We will have the precipitation, and there
will be some snow, but not really in the lower elevations. Going to
try something different tonight with the discussion, I will discuss
the overall weather pattern over the next couple of days first with
the players. Then, I will focus on the three main impacts,
precipitation amounts, potential snowfall and amounts and finally
potential for strong to high wind in portions of the area.

The low that will be bringing the precipitation today is now moving
onshore in northern California and will open a trough crossing the
Rockies late tonight and into tomorrow. The latest model trends have
been downward somewhat though with QPF, with the bulk remaining to
the south over Utah, Colorado and Arizona. We will see some here
though, with the heaviest precipitation in the west through midnight
tonight, tapering off after midnight after the trough axis passes
through the area. For areas East of the Divide, although there will
be some showers around this morning, the most numerous should be
tonight through Monday morning. Lee cyclogenesis will occur over
eastern Colorado late today and then the low will strengthen as it
moves northeastward into the Northern Plains states. This will
likely bring some wrap around moisture that will keep precipitation
going somewhat longer. However, it will also introduce a dry slot
that could keep amounts down somewhere. And this complicates the
rain and snow forecast somewhat. And finally, with the deepening
flow, the pressure gradient will tighten across the area. This will
bring the likelihood of strong wind to much of the area and
potentially high wind to portions of Johnson County. These main
impacts should end Monday evening as the low moves away to the east.
Now for the individual forecast elements.

Precipitation amounts...As was stated earlier, these have trended
down somewhat with core of the moisture remaining to the south.
However, all areas should see some precipitation. The wettest areas
at this time look to be 1) Far southern Wyoming, which will be
closer to the core of the deeper moisture; 2) The western facing
slopes in the western mountains with a period of favorable
orographic flow and 3) Favored northerly upslope flow areas East of
the Divide like the Wind River Basin south of Riverton and the
Lander Foothills, around Casper, the southern end of the Bighorn
Basin and the eastern Bighorns. As a counter, the least amounts
would be in 1) far northern Wyoming, which will be away from the
core moisture and 2) Areas of downslope, like the eastern Bighorn
Basin, the northern Wind River Basin and the Green River Basin.
However, there are still model differences on the placement of the
heaviest rain and the potential dry slot. Other differences are with
the amount of wrap around, as some have it further west than others.
As for amounts, most areas have at least a 1 in 2 chance of a
quarter inch of QPF or more, with the exception of the
aforementioned downslope areas. As for greatest chance of three
quarters of an inch or more, this would be mainly in the
aforementioned upslope areas. Some areas will likely see more than
an inch of QPF through the system though. Most should end by sunset
Monday, with all precipitation finished by sunrise on Tuesday.
CONFIDENCE IN AMOUNTS...Moderate to low.

Snow...For the most part, this looks like only the mountains for
this. Snow levels remain fairly high through this afternoon, ranging
from 8000 feet in the far west to 9500 to 10000 feet in eastern
portions of the area. The cooler air then works in as flow turns
north, falling as low as minus 3 to minus 4 by Monday afternoon.
This would drop snow levels down to 7000 to as low as 6500 feet.
However, the deepest moisture would be out of the area by then.
There could be some snowflakes mixed in or possibly a brief period
of wet snow in a place like Dubois, Meeteetse or areas along US 20
26 like Hiland, but accumulation would be slim to none. Most
mountains will see at least some accumulation though. The amount we
are most concerned with is 6 inches, which is needed for most
advisories. In the western mountains, this is largely restricted to
the highest elevations, so we will not issue highlights here. The
southern Absarokas have a 1 in 2 chance, but these are in areas with
no population and no impact. The Wind River Range does but we
already have an advisory for the western Wind River Range. I thought
about extending it to the eastern Winds but will hold off for now.
The other area of concern is the Bighorn Range, mainly the northern
portion west of Buffalo and northward. There is an area of a greater
than 1 in 2 chance of over 12 inches but it is in a relatively small
area with few people of impacts. In addition, the worst impacts
would not be until after midnight tonight. So, we will hold off of
issuing highlights for now. One complicating factor is the potential
for strong wind to increase impacts, we will touch on that in the
next section. And finally, we have Casper Mountain. There could be a
period of upslope flow here, but a lot depends on how much wrap
around moisture is present. Almost all snow here would be on Monday,
so we will hold off on any potential highlights for now. There is a
1 in 2 chance of 6 inches or more above 8500 feet on the highest
portions of the mountain. Almost all snow should end by sunset
Monday.
CONFIDENCE IN AMOUNTS AND PLACEMENT...Moderate.

Wind...Wind should remain fairly light through the day today except
for the favored southwest flow areas, even here is nothing unusual
for Wyoming though. The main time of concern will be from later
tonight after the flow turns northward and the pressure gradient
tightens, especially across northern Wyoming. There will be around
12 to 14 millibar pressure gradient from the eastern border of
Wyoming to Greybull. The 700 millibar winds are also rather
impressive, increasing to 50 knots across Johnson County from 12Z to
21Z on Monday. The NBM ensemble guidance gives a greater than 4 out
of 5 chance of wind gusts past 55 mph across northern Johnson
County. With this, we will hoist a high wind watch for this area
starting at 3 am and ending at 5 pm Monday. I also gave thought to
one for Bighorn County, but with the chance less than 1 out of 2 and
the main chance in the higher elevations I held off. The day shift
will have to watch this though and a warning may be needed if the
wind speeds trend up. Most areas east of a Cody to Riverton Line as
well as portions of southwestern Wyoming have at least a 1 in 2
chance of gusts past 40 mph so most places will see a blustery and
cool day, it will definitely feel like November in Wyoming. Wind
should decrease after sunset Monday as the low moves away and the
pressure gradient decreases.
CONFIDENCE IN WIND SPEED AND TIMING...Moderate to high.

Tuesday sees a return to more tranquil weather with somewhat warmer
temperatures. The next potential maker will be a fast moving low
moving in for Tuesday night into Wednesday. There is a rather
substantial model spread on this though, with some bringing some
showers to the state Wednesday and others keeping the system south
of the area as high pressure builds in from the north. Riding should
then bring mainly dry weather for the end of next week with near to
somewhat above normal temperatures.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 339 PM MST Sun Nov 1 2026

Light rain continues to overspread western Wyoming, and will
bring lower vis and cigs through the nighttime hours. Still
expecting all sites to be below 1500 ft through the night, with
most locations holding at or below IFR conditions. KCOD LIFR
cigs and vis will last through sunrise, with some rain/snow mix
around that time. Conditions west of the Divide will start to
improve between 12Z and 14Z, with an end of precip and gradual
thinning of cigs. North to northwest winds will also increase
overnight as the cold front sweeps southward. Most areas will be
gusting 25 to 30kts for a few hours around frontal passage, with
a gradual decrease during the day Monday.

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...
Winter Weather Advisory from 1 AM to 9 AM MST Monday for
WYZ009.

Winter Weather Advisory from 3 PM to 5 PM MST Monday for
WYZ009-015.

High Wind Warning from 3 AM to 3 PM MST Monday for WYZ010.

Winter Weather Advisory until 5 AM MST Monday for WYZ014.

Winter Weather Advisory from 8 PM this evening to 9 AM MST
Monday for WYZ015.

&&

$$

UPDATE...Wittmann
DISCUSSION...Hattings
AVIATION...Straub