144
FXUS65 KRIW 181743
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1143 AM MDT Sat Oct 18 2025

.KEY MESSAGES...

- Rain and snow are coming to an end across Wyoming this
  morning. Skies will quickly clear through the afternoon, with
  chilly temperatures in the 40s and 50s.

- An approaching Pacific system will bring light to possibly
  moderate snow to the northwestern mountains late Sunday and
  Sunday night.

- Gusty to strong wind is expected Sunday into Monday across
  much of the area.

&&

.DISCUSSION...
Issued at 258 AM MDT Sat Oct 18 2025

It has always been my preference with things I don`t like, if I have
a choice, is that I get it over with early. And if you don`t like
active weather and prefer more tranquil, quiet and more pleasant
autumn weather, this forecast will be similar. Almost all the active
weather in this forecast is contained in the first 72 hours, with
relative quiet conditions for the remainder.

The have two systems to talk about. The first, in the form of a
Canadian cold front, is now dropping southward through Wyoming.
Radar does show some showers with it.  However, we have no
highlights with it. For one, it is of continental origin and does
not have an ample amount of moisture to work with. It also a fast
moving system, with all showers over by around noon. The chance of
any accumulating snow of over an inch of snow or more is restricted
to the northern mountains. The chance of over 3 inches of snow is at
most 1 out of 3 in the southern Absarokas with almost zero chance of
6 inches. However, in areas expected to see the most showers,
especially portions of Johnson and Natrona Counties, see some snow
in the air this morning and possibly a small coating on non paved
surfaces. As for total precipitation amounts, only the area from the
Bighorns through Johnson County has a greater than 1 out of 2 chance
of a tenth of an inch or more, excluding the western mountains. Wind
will be gusty with the frontal passage, with a greater than 2 out of
3 chance of wind gusts past 30 mph in the favored northwest flow
locations, like Greybull, Buffalo as well as Rock Springs. Wind
should decrease as the front moves away in the afternoon though. It
will bring cooler temperatures though, around 10 to 15 degrees
cooler than on Friday.

After a dry period this afternoon through Sunday morning, the second
system, this one a Pacific trough and cold front, will approach from
the west. The concerns are similar with this one, mainly
precipitation and wind. We will tackle each one individually.

As for precipitation, with the Pacific origin, it does have more
moisture to work with than this mornings front. However, most
guidance shows it splitting as it approaches Wyoming. And as a
result, this should limit amounts somewhat. Most probabilistic
guidance is focusing mainly on southern Absarokas, where there is
around a 3 out of 5 chance of 6 inches or more. However, there are
basically no people here and as a result impacts look rather
minimal. The one area of concern may be Togwotee Pass, where there
is a 1 out 2 chance of 6 inches or more as well. Elsewhere, it is
less than 1 out of 2. Like the previous system, it also a fast mover
with most rain and snow falling an a 12 to 18 hour period, with most
through the area by sunrise on Monday. As for the lower elevations,
there is a 4 out of 5 chance of less than a quarter of an inch of
precipitation in the lower elevations. With the westerly flow with
the system, downsloping flow may keep many locations East of the
Divide mainly dry. The best chance will be across northern Wyoming,
but even here, amounts should be generally light, except for the
Bighorns where upslope flow may bring should bring a few inches of
snow.

Now for the windy part of the system. The main area of concern for
this looks to be across the southern half of the area, which will
closer an 140 knot jet core moving across that region. The main time
of concern looks to be Sunday afternoon and evening in southwest
flow, prefrontal locations, like Rock Springs, Casper and even
Lander. Guidance is showing some 50 knot wind barbs at 700
millibars, and with the front approaching there will be ample mixing
as well. Probabilistic guidance is on the fence though. Casper
itself has only a 2 out of 5 chance wind wind gusts past 55 mph. The
areas that have the best chance are higher elevation locations that
have little impact. For now, we will hold off on any highlights. The
most impacts would not be until Sunday afternoon. The day crew can
take a another look and issue watches and we can upgrade tomorrow
night if needed. As for the post-frontal, northwest flow locations,
like the Wind River Basin, Big Horn Basin and Johnson County, the
chance of wind gusts past 55 mph is again, less than 2 out of 5 for
the most part. We will let the day crew re-evaulate. Wind should
decrease in the southwest flow areas Sunday night, but continue in
the northwest flow locations much of the night.

After a mild day Sunday, temperatures will again drop behind the
front for Monday. Some showers will continue in the unstable,
northwest flow, but any amounts would remain light. It will feel
chilly though with temperatures 10 to 20 degrees cooler than Sunday
Another jet max moving over the area Monday will keep the wind going
in northwest flow area, but the chance of gusts past 50 mph drops to
at most 1 out of 3 on this day.

We then enter the more tranquil portion of the forecast as flat
ridging builds over the state for the rest of the week, bringing
near normal temperatures and mainly dry conditions. There will be
some locally breezy conditions in the favored locations, but noting
notable. One small fly in the ointment is a wave passing over
Colorado that could bring a few showers to far southern Wyoming
Wednesday night, but this is far from certain as guidance is all
over the place. The next decent chance of precipitation would likely
hold off until next weekend as the next Pacific system approaches
from the west.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1142 AM MDT Sat Oct 18 2025

Low clouds and snow showers continue to exit the region to start the
period. KCPR and KLND will hold onto the SCT to BKN decks near FL030
at the start of the period, but will see those decks scatter out by
20Z. Only FEW to SCT high clouds will remain and VFR conditions will
prevail at all terminals through the period. KBPI, KPNA, and KRKS
terminals will see gusty west winds during the afternoon, with gusts
around 25kts expected. These will decrease after 00Z and light winds
(less than 10kts) will then prevail through the night. Winds at most
terminals will begin to increase late in the period as another quick-
moving weather system pushes in.

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.

&&

$$

DISCUSSION...Hattings
AVIATION...Hensley