466
FXUS65 KRIW 031842
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1142 AM MST Tue Mar 3 2026

.KEY MESSAGES...

- The remainder of today is mild and sunny, with light winds.

- Mild and dry Wednesday, with elevated fire weather from Muddy
  Gap through Natrona County.

- The next weather system has good potential to bring
  accumulating snow to much of the area Thursday and Friday.

&&

.UPDATE...
Issued at 1139 AM MST Tue Mar 3 2026

No notable changes to the forecast for the next 24 hours. Today
remains a pleasant day, with sunshine, mild temperatures, and light
winds. Tomorrow, ahead of the next incoming weather system, winds
increase across the usual locations, like mountains and Wind
Corridor. Relative humidities (RH) also drop, especially east of the
Divide. For fire weather concerns, the areas of greatest concern
would be Johnson/Natrona Counties, where RHs are lowest and winds
highest. However, the stronger winds will be over Natorna County,
with the lowest RHs over northern Johnson County. Though there could
be isolated areas where critical fire conditions occur, this seems
more like a widespread elevated fire day, so have held off on
highlights for now.

In regards to the winter system Thursday and Friday, models have (as
predicted) slowed the onset of snow over the west to be late
Wednesday night to early Thursday. There is still some uncertainty
with the track of the system, so have held off on any highlights. It
should be noted that snow totals have not changed much, so there is
a little consistency now.


&&

.DISCUSSION...
Issued at 242 AM MST Tue Mar 3 2026

It is often said that sports are a matter of inches, with games
being decided by a very small margin. That remains me of the
forecast I made last night for rainfall amounts in central
Wyoming, but in a matter of a small number of miles versus
inches. It called for a quarter to a half an inch of rain in
places like Casper and Riverton. Well, that has not materialized
with only light rain and very light amounts. However, just go
to 25 miles to the south and Lander has around a quarter of an
inch or rain and it is still raining as of 2 am. I have to eat
a little crow on this.

As expected, the heaviest is across southern Wyoming. The area of
low pressure shows up across southwestern Wyoming, working its way
slowly to the east near the Wyoming / Colorado line. There is some
decent snow falling in Lincoln County at this time with some
enhancement by the left front quadrant of a jet streak, a bit more
than I thought last night. We will go ahead and issue a short term
Winter Weather Advisory for snow. Of more concern is Sweetwater
County, including Interstate 80. The HREF ensemble is showing a
greater than 1 in 2 chance of 3 inches to east of Rock Springs.
Amounts are borderline, but for impacts, especially to
Interstate 80, we will again issue a Winter Weather Advisory.
Elsewhere, rain and snow should end from north to south and be
basically over by around noon with increasing amounts of
sunshine following that. Temperatures will remain mild in areas
with no snow, again averaging well above normal.

Wednesday looks like a quiet day as well, for the most part. The one
concern is from Muddy Gap through Casper where a gusty wind will
develop ahead of the next system moving in from the west. As for
fire weather highlights, we will definitely have the wind with some
gusts to 40 mph possible. The question is humidity. As of now,
HREF ensemble guidance is only giving less than a 1 out of 2 chance
of relative humidity falling below 20 percent, with only a 1 out of
10 chance below 15 percent. So, we will hold off on any fire weather
highlights for now. If conditions worsen, the day shift can issue a
watch and we can upgrade if needed tomorrow night.

Then we look toward what looks to be the main story for the rest of
the week. This is in the form of another Pacific system that will
approach from the west. At this point, this one looks to have a good
setup for a decent snow across much of the area. There will be lee
cyclogenesis occurring over Colorado, turning flow more
easterly then northerly, bringing in moisture and then good
north to northeasterly upslope flow. The 700 millibar low may be
tracking across the Wyoming-Colorado border, a good location
for a decent storm. Details are still highly uncertain in
regards to placement of timing of heaviest precipitation though,
as the GFS and European have performed a Freaky Friday swap and
are polar opposites of what they showed yesterday. A few things
I am fairly confident on. One is that the timing in the current
forecast is the fastest the precipitation would move into
western Wyoming. Personally, I think all areas will stay largely
dry through midnight with only light precipitation through late
Wednesday night. Even most of Thursday should stay dry East of
the Divide, with the bulk of the precipitation holding off until
after sunset. It will also start warm, so the precipitation may
begin as rain before changing to snow, in most areas by
midnight Thursday night and all locations by sunrise Friday and
then possibly continuing through the day. As for a first guess
at amounts, most ensemble guidance gives at least a 2 out of 3
chance of 3 inches or more for most of the area, with at least a
1 in 2 chance of 6 inches or more in the favored northerly
upslope areas like Thermopolis, Lander and Casper. We will
almost certainly need some highlights for this storm but it is
too early at this time. Following this, high pressure should
bring dry weather for the weekend. Temperatures may be lower
than what is in the forecast given the fresh snow cover, but
with the Pacific origin of the air, it will not be bitterly
cold. This, combined with the strong March sun, should begin
melting the snow over the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1009 AM MST Tue Mar 3 2026

A few areas of lower clouds linger over KPNA and KRKS to start
the period. However, conditions are expected to quickly improve
with all terminals to see VFR conditions for the remainder of
the period. Skies will gradually clear with SKC for numerous
terminals with high level clouds building in late this evening.
Winds are forecast to remain light across all terminals with a
few breezes around 20 knots possible at KCOD and KRKS. Winds
increase slightly late Wednesday morning with KCPR seeing winds
around 25 knots by the end of the TAF period. Some areas of
mountain obscuration will be possible through the first half of
the TAF period as clouds continue to dissipate.

&&

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

&&

$$

UPDATE...Wittmann
DISCUSSION...Hattings
AVIATION...Dziewaltowski