215
FXUS65 KRIW 291800
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1200 PM MDT Thu Oct 29 2026

.KEY MESSAGES...

- A pleasant day today with increasing high clouds and highs in
  the 50s to low 60s. A similar day is in store on Friday.

- Shower chances (20% to 50%) increase across western and
  southern Wyoming Friday afternoon through Saturday morning.
  Precipitation amounts are forecast to be under 0.10" during
  this time frame.

- There is fairly high confidence in widespread showers Sunday
  into Monday, with a 60% chance of moderate snow in the
  mountains.Exact timing and placement of the heaviest
  precipitation remains somewhat uncertain.

&&

.UPDATE...
Issued at 1200 PM MDT Thu Oct 29 2026

Midday satellite imagery shows high clouds over the Great Basin
shifting northeast into Wyoming. These upper level clouds and
moisture coincides with a weak shortwave embedded within the
southwest flow aloft. As the shortwave treks northeast this
afternoon and evening, anticipate high clouds to increase. Despite
the increasing cloud cover, temperatures are forecast to reach the
50s and low 60s for most low elevation areas. However, if cloud
cover increases faster than expected, temperatures will be a few
degrees cooler than what is currently forecast.

The aforementioned shortwave will traverse over Wyoming from roughly
midnight through sunrise Friday. As it does so, there may be just
enough moisture and orographic lift for light snow to fall across
Yellowstone National Park. A stray light rain shower cannot be ruled
out (less than 15 percent chance) across the Green River and Wind
River Basins after sunset tonight. Otherwise, another shortwave
approaches Wyoming on Friday afternoon. There will be a bit more
moisture accompanying Friday`s shortwave, thus precipitation chances
(20% to 50%) exist across southwest and western Wyoming Friday
afternoon through Saturday morning. Only a few hundredths of
precipitation are forecast Friday into Saturday morning, but don`t be
spooked if you see a wet ground Saturday morning!

&&

.DISCUSSION...
Issued at 205 AM MDT Thu Oct 29 2026

Early this morning, I am listening to old school rhythm and
blues. When I turned to the station, it was a rather convenient
coincidence that the first song I listened to describes the
weather across much of the area today. Shortwave ridging will
build across the area today, and bring a dry day with above
normal temperatures for late October. Some mid to high level
clouds will move in at times, but nothing other than that. If
you are still wondering about what the song that describes the
weather today, it is "Lovely Day" by the late, great Bill
Withers. So if you can, get out an enjoy it. Dry weather will
continue through tonight, but more clouds may keep temperatures
a bit warmer than Wednesday night.

The pattern begins getting more active following today. Clouds will
increase Friday as moisture deepens ahead of a shortwave moving in
from the southwest. Guidance continues to trend slower with the wave
though. Most of the area will have a dry Friday with another day of
above normal temperatures. Some locations, like Casper, will be well
up into the 60s. As for precipitation, we can`t rule out a shower in
southwestern Wyoming. However, the chance is less than 1 out of 6
and most showers would not occur until after sunset Friday night.

Guidance has also trended somewhat drier for Saturday. The main
showers will be across western and southern Wyoming again, with
diminishing chances further north and east. But even in the west,
amounts look rather light, generally a tenth of an inch or less.
Although the forecast East of the Divide is dry right now, we
can`t rule out a shower in some locations. Chances are rather
low at this time though, generally less than 1 out of 7, and
most locations East of the Divide would likely remain dry
through at least Saturday evening. As for the trick or treating
weather, most guidance shows mainly dry conditions for most of
the area Saturday evening with at most a 1 in 4 chance and that
would be in the far west. It will be another fairly mild day as
well. So, things look good for all the kiddos to get their
annual sugar rush from the various forms of candy (save a
Snickers bar for me).

All eyes are still looking at what will happen Sunday into Monday.
We continue to have a complex set up, and details still remain
somewhat uncertain at this time. There is a bit more agreement at
this time though with the general pattern. The two main players are
an upper level low that will drop southward along the Pacific
Northwest Coast and move onshore in northern California Saturday
night and another, much wetter low that will move onshore in
southern California on Sunday. It looks like these two systems will
phase to the south of Wyoming and continue East, with lee
cyclogenesis occurring over Colorado Sunday night. The deepest
moisture will remain to the south of Wyoming, over the desert
southwest and over portions of Utah and Colorado. This should keep
amounts down somewhat. And continuing the trend, the system is
slower. All areas will have a chance of showers on Sunday, but most
will be across western Wyoming. The wettest period looks to be
Sunday night into Monday morning as the low moves eastward. There is
a new wrinkle in a few of the models for Monday. It is that some
ensemble runs, as well as the operational European model, show a
good area of wrap around moisture that could impact areas East of
the Divide Monday into Monday night. This is the first run showing
it though, so I`m not completely buying into it yet. We will
continue to watch it though to see if it persists though.

Now we move on the precipitation amounts, in the 48 hour period
ending Tuesday at 6 am, the NBM ensemble guidance shows most areas
having at least a 1 in 2 chance of a quarter of an inch of
precipitation, with the highest chance in the mountains. Areas with
a greater than 1 out of 2 chance of 0.75 inches or more are
generally confined to the mountains. The greatest chance will be in
the western mountains, where a period of orographic enhancing
westerly flow will bring heavier amounts, as well as in the
Bighorn Range, more from the possible wrap around moisture.

And the question more people are wondering about, will there be snow
and how much and where? One change today is the most guidance has
trended warmer, so the chance of accumulating snow in the lower
elevations is looking less likely (less than a 1 out of 3 chance at
this time). Snow levels look to remain fairly high through Saturday
night. The 700 millibar temperatures are expected to remain
near to above 0 degrees celsius, putting snow levels at 8500
feet or higher. This could still impact some mountain passes
though, especially Togwotee Pass. Colder air then moves into the
area as the low passes and flow turns to the north. There is
still a difference on the models with snow levels past this
though, with differences of up to 1500 feet. At this time, most
guidance shows some snow in the western valleys, although
amounts will be on the light side. As for the first guess of
accumulations, there is a greater than 1 in 2 chance of 6 inches
of new snow across most of the mountain ranges above 9000 feet
through the event. The chance of a foot or more is largely
restricted to the highest elevations though. My first guess
would be that we may need some winter weather advisories for
some of the mountains with the impact to passes but nothing
more. As for the East of the Divide lower elevations, the best
chance would be above 6500 feet on Monday as the cooler air
moves in. This would include places like Dubois or possibly the
south side of Casper, but accumulations would be light, an inch
or less.

Following this, ridging will build back over the Rockies for much of
next week. This bring a period of tranquil weather with near to
somewhat above normal temperatures and dry conditions. Looking way
out, the next chance of showers might be next weekend, but details
are obviously impossible to nail down this far out.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1047 AM MDT Thu Oct 29 2026

VFR conditions to prevail across all terminals through the TAF
period. Winds remain light around 5 to 10 knots with occasional
gusts nearing 15 knots at locations such as KCPR and KRKS. High
level clouds gradually build in through the afternoon with
ceilings lowering by Friday ahead of a nearing disturbance.
Conditions remain dry for the period with precipitation chances
beginning to increase by the end of the TAF period. Mountains
should remain mostly unobscured for nearly if not all of the TAF
period.

&&

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

&&

$$

UPDATE...Gerhardt
DISCUSSION...Hattings
AVIATION...Dziewaltowski