669
FXUS65 KRIW 162015
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
115 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 River 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 an
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 River 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 700 mb 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 River 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 700 mb 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 700 mb 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 be 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 /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1057 AM MST Sun Nov 16 2025

VFR conditions persist through 00Z/Monday as southerly flow ahead of
an upper low over Nevada spreads mid and high clouds across the
region. Light showers skirt the western border in the vicinity of
KJAC Sunday afternoon. The better chance for showers arrives
over the southwest terminals between 01Z-03Z/Monday as a wave of
moisture lifts north ahead of the upper low. This initial wave
continues north to a KJAC-KRIW-KCPR line around 06Z/Monday.
Widespread MVFR is anticipated in association with this wave,
and localized IFR occurs at KRKS, KPNA, and KBPI where rain
changes to snow later tonight. The upper low tracks into
southern Wyoming by sunrise Monday with the associated 700 mb
circulation set to move across central Wyoming 09Z-15Z/Monday.
This leads to a period of enhanced precipitation before
downsloping northwest flow arrives by midday Monday. Conditions
improve at terminals west of the Continental Divide around
18Z/Monday. Widespread mountain obscurations after 03Z/Monday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 PM this afternoon to 5 PM MST
Monday for WYZ012-014-024.

&&

$$

UPDATE...Gerhardt
DISCUSSION...Hattings
AVIATION...CNJ