515
FXUS65 KRIW 290553
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1153 PM MDT Wed Oct 28 2026

.KEY MESSAGES...

- Clear skies and light winds overnight into Thursday morning
  that will give way to a chilly start with most below freezing
  even east of the Divide.

- Mainly dry and tranquil weather will continue Thursday, with
  all but far western Wyoming remaining dry through Friday.
  Temperatures will average 8 to 12 degrees above normal on
  Friday from Rock Springs to Casper and Buffalo.

- A weather system may bring more substantial rain and mountain
  snow Sunday into Monday, but details in placement and amounts
  of the heaviest rain and snow remain rather uncertain.

&&

.UPDATE...
Issued at 1132 AM MDT Wed Oct 28 2026

Precipitation amounts of 0.05" to 0.15" occurred last night from
southern Lincoln County to Fremont and Natrona counties with the
passage of the cold front. Locally higher amounts up to 0.2" between
Kemmerer to South Pass. Low clouds/fog in the Upper Green River
Basin to South Pass this morning will continue to lift and scatter
out through 20Z (2pm). Otherwise, conditions will remain dry with
mostly clear skies and light winds. Wind gusts of 25 to 30 mph will
occur from South Pass to Casper and over the mountains/Yellowstone
through the afternoon. Freezing temperatures will be widespread
tonight under mostly clear skies and light winds. Similar conditions
from today will return Thursday with lighter winds and increasing
clouds in the afternoon.

&&

.DISCUSSION...
Issued at 303 AM MDT Wed Oct 28 2026

The forecast is again working out fairly well this morning as
some jet enhanced precipitation is currently working its way
across roughly the southern half of the area, including here at
the humble Riverton Weather Abode. It is rain at our office
right now, but there has been some snow in places like Pinedale
and Big Piney. A few lightning strikes have also been noted.
Almost all showers should end by sunrise today. However, there
will likely be some slick spots on roads that saw snow. And, a
few locations have seen the fog monster crawl out of this lair
to feed on the moisture from the precipitation.

Once the showers end, ridging should build across the area and
bring at least two days of fairly tranquil weather with many
areas having three days of fairly quiet weather, lasting through
Friday. There will still be somewhat of a pressure gradient in
the wind prone areas from Muddy Gap through Casper so a gusty
wind will continue there, but not nearly as strong as yesterday.
Wind should decrease through Friday as well. Temperatures will
also be on the rise. The temperatures in the forecast today are
probably the coolest it will be. I could see it 3 to 5 degrees
higher on each day. The warmest day looks to be Friday when
places like Casper may be well up into the 60s.

The next chance of showers will begin to move into western
Wyoming as a trough rotates around an upper level low off of the
Pacific Northwest Coast and brings increasing moisture to the
area. There continues to be disagreement in the guidance in
regards to placement and intensity of the showers, with some
models, like the GFS, keeping things mainly dry through most of
Saturday. For now, most areas have some chance on Saturday but
most places should be dry most of the time.

The most interesting feature of the forecast though is from
Sunday into Monday. There is an interesting and complex
situation setting up. We have two main players. The first is the
aforementioned upper level low that will get kicked eastward
into the Rockies Sunday night and into Monday. Another player is
an area of low pressure from further south in the Pacific Ocean
that will move into southern California on Sunday and track
east to northeastward into the Southern Rockies. The big
question is how will these systems interact, how much moisture
from the much wetter southern system can get drawn northward and
if the systems phase and where will they phase. The guidance of
both the deterministic and ensemble varieties, continues to
have a rather wide spread in regards to all of these variables.
In the deterministic realm, the ECMWF phases the systems
further eastward and is slower, which would mean a wetter
solution. The GFS is faster and drier, with the phasing and
deepening of the low further east. So, although we are fairly
confident of at least some unsettled weather across the area,
precipitation amounts and the placement and timing of
precipitation remains highly uncertain. A first look at the NBM
ensemble gives at least a 1 in 2 chance for most areas to get at
least a quarter of an inch or QPF from Sunday morning through
Monday evening. As for snow, the 1 in 2 chance of 6 inches over
the same time frame is largely confined to the mountains above
8000 feet. It could get cold enough for lower elevations to see
the first snowflakes of the year, but chances of decent
accumulations of greater than 2 inches remains low, under 1 out
of 4 at this time. But remember, this is still 5 days out so a
lot can and probably will change. Stay tuned as we get closer
to the event for more clarity. After this system departs, there
is good model agreement in ridging building over the area,
possibly bringing dry and tranquil conditions for much of next
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1152 PM MDT Wed Oct 28 2026

VFR conditions expected through the entirety of the period at
all TAF sites. Light winds overnight into Thursday morning with a
few high clouds pushing in from the southwest. Winds increase to 8-
10kts after 16-18Z with daytime heating and mixing to the surface, a
bit stronger at CPR with gusts up to 18kts. Increasing high clouds
through the afternoon and evening as winds decrease after 00Z
towards sunset with radiational cooling. Dry conditions expected
with no other weather elements at this time.

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...
None.

&&

$$

UPDATE...LaVoie
DISCUSSION...Hattings
AVIATION...Lowe