879
FXUS65 KRIW 031116
AFDRIW

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

.KEY MESSAGES...

- Rain and snow will end this morning, with increasing sunshine
  through the afternoon.

- 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.

&&

.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 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 /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 414 AM MST Tue Mar 3 2026

Precipitation remains limited to KRKS this morning, with low
clouds, fog, and snow continuing there through about midmorning.
Remaining sites have all shifted to VFR as skies have quickly
begun to clear. Expect VFR at all sites by 18Z, and continuing
at all sites through the next 24 hours.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 8 AM MST this morning for WYZ027.

Winter Weather Advisory until 11 AM MST this morning for
WYZ028>030.

&&

$$

DISCUSSION...Hattings
AVIATION...Straub