447
FXUS65 KRIW 162236
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
336 PM MST Sun Nov 16 2025

.KEY MESSAGES...

- Scattered western mountain snow and valley rain chances
  (30-60%) through the afternoon hours today, with mainly dry
  conditions elsewhere.

- Rain and mountain snow chances (60-100%) spread south to north
  across the state after sunset Sunday and continue through
  midday Monday. The heaviest precipitation is expected during
  the early Monday morning hours.

- A Winter Weather Advisory is in effect for the Teton and Gros
  Ventre Mountains, the Salt and Wyoming Mountains, and the
  western Wind River Mountains from 5 PM Sunday through 5 PM
  Monday. The heaviest snow is forecast between 11 PM tonight
  and 7 AM Sunday.

- The upcoming week is trending toward near normal temperatures
  and a more active period of showers (40-60% chance),
  specifically Wednesday into Thursday. There remains
  uncertainty in exact timing as well as rain and snow amounts.

&&

.UPDATE...
Issued at 114 PM MST Sun Nov 16 2025

A few changes have been made this forecast package as guidance has
become a bit more aligned in the track and moisture content of the
Sunday night weather system. 19Z water vapor satellite imagery shows
a Pacific low now onshore and circulating over Nevada as well as
a vorticity maximum over western Wyoming. This vorticity maximum
combined with an influx of moisture, thanks to the
southwesterly flow, will support an area of scattered mountain
snow and valley rain through sunset Sunday.

As the western precipitation chances wane, the upper-level low will
approach southwest Wyoming. Abundant moisture will accompany the
upper low given it`s Pacific origin. In fact, 12Z precipitable water
amounts at southwest CONUS upper air locations range from 0.54" to
0.58" associated with this upper low, roughly in the top decile of
climatological observations. Given the moisture content, forecast
QPF has been increased across the forecast area, especially across
the Salt and Wyoming Ranges and the western Wind River Range.
There is an 80% chance of at least 1" of liquid water amounts
over the Salt River Mountains, and a 70 to 90% chance of 0.5" of
liquid water over the remaining western mountain ranges.

Guidance is in better consensus Sunday in showing the upper low
trekking from southwest to northeast Wyoming tonight and Monday. The
associated 700mb low will track from southwest Wyoming across
the Wind River Basin to the Black Hills. Widespread
precipitation chances (60-100%) exist tonight and Monday as the
low moves eastward. The heaviest precipitation is forecast to be
between 11 PM tonight through 7 AM Monday, with mountain snow
and low elevation rain. Because the QPF has been increased today
and given the timing of heaviest precipitation, snow amounts of
6 to 11 inches will be common across the previously mentioned
mountains. Thus, the Winter Weather Advisory has been expanded
to include the Salt and Wyoming Ranges and the western Wind
River Range. Rain is forecast to change to snow across portions
of Sublette and Sweetwater Counties given the relative higher
elevations (6K to 7K feet MSL), dynamic cooling, and colder air
filtering in behind the low. Amounts will generally be less than
one inch.

However, this system is not too cold with 700mb temperatures
still forecast to only drop to around -3C west of the Divide
and -1C east of the Divide at the time of precipitation. This
reflects snow levels around 7,000 ft west of the Divide and
8,000 ft east of the Divide. Overnight lows east of the Divide
will struggle to fall below 35F-40F degrees given dense cloud
cover. So, precipitation will fall as a good soaking rain for
the Wind River Basin with liquid amounts of 0.25"-0.5" through
Monday evening. Other areas can expect around 0.10"-0.25"
through Monday evening. Rainfall east of the Divide is expected
to come in two waves. The first wave impacts central Wyoming
between 11 PM Sunday and 4 AM Monday as lift is enhanced with
the 700mb low passing overhead. The second wave of rain quickly
arrives behind the low as flow becomes more northwesterly
between 5 AM and 9 AM Monday. Precipitation should largely end
or become more isolated by Monday afternoon as cooler and drier
northwest flow filters in.

&&

.DISCUSSION...
Issued at 112 AM MST Sun Nov 16 2025

It looks like the honeymoon of the unusually mild weather we
have had for the first half of November is coming to an end and
the weather will be giving us a slap back into reality. Radar is
showing some echoes across western Wyoming this morning, but
basically none are reaching the ground as of 1 am. Today
continues to look drier as guidance continues to slow the
arrival of the precipitation. As a result, we have lowered PoPs
and QPF through the daylight hours. Today will be one more mild
day, especially east of the Divide which will likely be dry
through the daylight hours. Many locations will see highs in the
60s, likely for the last time this calendar year. A gusty
breeze will again develop across the Wind Corridor from Muddy
Gap through Casper, but high wind is not expected.

Precipitation will overspread much of the area between tonight and
Monday, with the steadiest and heaviest expected from midnight
through noon on Monday as the best upper level divergence and jet
support move over the state. The reasoning of the forecast
remains fairly similar to yesterday. The area of most concern
will be the Tetons, where Teton and Togwotee Pass have a
greater than 1 in 2 chance of 6 inches of snow or more through
the period. Given the possible impacts to travel over Teton and
Togwotee Passes, we went ahead and issued a Winter Weather
Advisory for this zone, although it was borderline. Other areas,
like the highest elevations of the Salt and Wyoming Range as
well as the western Wind River Range also have at least a 1 in 2
chance of 6 inches of snow or more. However, these are away
from the passes and with impacts expected to be limited we
elected to hold off for now. The day shift can take another look
and see if any additional highlights are needed since the
greatest impact would not be until later tonight.

This will be mainly a mountain snow event though. The 700 millibar
temperatures generally only fall to around minus 3 Celsius,
which would put snow levels around 7000 feet. And this is by
Monday morning, when the best lift moves out of the area.
Places like Bondurant could see a couple of slushy inches and
even Pinedale could see a slushy inch or so. The Jackson and
Star Valleys would likely only see a coating. Odds are less than
1 out of 3 for three inches in all these areas, so we will not
issue any advisories. As for east of the Divide, with 700
millibar temperatures only falling to minus 1 Celsius, snow
levels should remain above 8000 feet, with only rain for the
populated areas. There are still some disagreement on placement
of the heaviest amounts though, so we broadbrushed things for
now. Most precipitation should end from south to north starting
Monday afternoon as the upper level low moves away to the north
and east.

Cooler weather then moves in for Monday through much of next week.
However, with flow largely west or southwesterly, temperatures will
remain near to somewhat above normal through the week. Tuesday looks
mainly dry with only a few showers in northern Wyoming. Following
that, we have the same conundrum as previous days. We do look more
unsettled through the period. However, there are still large
disagreements in the guidance in regard to timing and movement of a
couple of systems moving through. So, although confidence remains
fairly high in a cooler and more unsettled pattern, details remain
highly uncertain.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 323 PM MST Sun Nov 16 2025

An upper low over the Great Basin tracks northeast tonight and into
southern Wyoming by 12Z/Monday. Southerly flow ahead of this feature
generates a wave of showers that initially tracks into southwest
Wyoming between 01Z-03Z/Monday. Precipitation spreads farther north
to a line from KJAC-KRIW-KCPR between 05Z-07Z/Monday, and MVFR
conditions become widespread along and south of this line.
Temperatures favor light snow developing across southwest Wyoming
early Monday morning with IFR conditions becoming more common at
KRKS, KPNA, and KBPI. A 700mb circulation is set to move over
central Wyoming between 09Z-15Z/Monday. This leads to a period
of enhanced precipitation before downsloping northwest flow
arrives by midday Monday. The northwest flow allows for
improving conditions between 16Z-20Z/Monday at terminals west of
the Continental Divide and at KRIW and KLND. MVFR ceilings and
light rain linger around KCPR through Monday afternoon. Gusty
southerly surface wind late tonight, especially at KRKS and
KCPR, gives way to gusty west to northwest wind Monday
afternoon. The strongest wind of 20-35kts blows at KRKS
beginning around 12Z/Monday. Widespread mountain obscurations
occur between 03Z and 18Z/Monday with mountain top obscurations
persisting through the entire period.

Please see the Aviation Weather Center and/or CWSU ZLC and ZDV for
the latest information on smoke, icing, and turbulence
forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST Monday for WYZ012-014-
024.

&&

$$

UPDATE...Gerhardt
DISCUSSION...Hattings
AVIATION...CNJ/LaVoie