045
FXUS65 KRIW 062257
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
357 PM MST Thu Mar 6 2025

.KEY MESSAGES...

- Winter storm impacts continue across the forecast area
  Thursday afternoon and night. Winter Storm Warnings and Winter
  Weather Advisories remain in effect for nearly all of western
  and central Wyoming through early Friday morning.

- A 6- to 9-hour period of enhanced snowfall occurs across
  Thursday night as a mid-level circulation moves across central
  Wyoming. The heaviest snow will occur over portions of central
  and south-central Wyoming.

- Snow ends from northwest to southeast by midday Friday,
  persisting longest in Natrona County. Afternoon snow showers
  linger, but accumulation will be limited. Temperatures remain
  unseasonably cool Friday, but warm enough that snow will begin
  to melt.

- Dry and warmer conditions arrive for the weekend, with daytime
  high temperatures rising to normal or slightly above normal.

- The next chance (30-40%) of a significant storm system comes
  next Thursday, with the best chance of precipitation across
  western and southern Wyoming.

&&

.UPDATE...
Issued at 1210 PM MST Thu Mar 6 2025

Low-level northeast flow with overrunning moisture streaming
north across the forecast area continues at midday Thursday.
Several circulations are rotating through the broad trough
located in the Great Basin. Models have been fairly consistent
in a 700-500mb circulation traversing the region beginning late
Thursday afternoon through the early Friday morning hours. The
heaviest snow occurs within a 6- to 9-hour period centered on
the 00Z-06Z/Friday timeframe. While jet dynamics will have
shifted well to the southeast of the state by Thursday evening
and 700-500mb lapse rates are marginal, the combination of the
moisture, circulation, and favorable mid-level temperatures for
dendritic growth will aid snowfall production. SREF plumes
confirm this trend toward higher totals during this 6- to 9-hour
period. Adjustments were made to precipitation chances from
Natrona County to central/eastern Sweetwater County to account
for an axis of heavier snow on the backside of the mid-level
circulation. QPF trends, especially for portions of Sweetwater
County, also support the increase in precipitation chances.
Easterly surface wind gradually shifts to the north overnight
as the circulation trudges east. A period of gusty northeast
wind and moderate to heavy snow provides widespread blowing snow
and reduced visibility across Natrona County overnight.

The trough axis remains over Wyoming through Friday, but much of the
moisture and energy shifts to our east by sunrise Friday. Light snow
lingers longest across Natrona County with northerly upslope flow
persisting. Clearing will be slow in cold, cyclonic flow. For those
areas where the sun peaks through Friday afternoon, the presence of
a cold pool aloft will lead to the redevelopment of stratocumulus.
The instability and cyclonic flow allows for lingering light snow
showers, particularly over the higher terrain. However, additional
accumulations will be minimal from late Friday morning onward. The
arrival of surface high pressure from the north will confine gusty
east-northeast wind to Sweetwater County Friday afternoon. All areas
clear Friday night as a foldover ridge pushes in from the west.
Warmer air aloft, a clearing sky, and abundant low-level moisture
should lead to patchy/areas of fog by sunrise Saturday.

&&

.DISCUSSION...
Issued at 115 AM MST Thu Mar 6 2025

An emerging baroclinic leaf is moving over the Cowboy State as of
0530Z and somewhat disorganized. Moisture is beginning to increase
over central portions as well, as denoted by very weak echoes
visible on radar. The timing of the snow will likely be pushed
forward several hours as the air is still very dry. Dewpoints at
Riverton, Casper, Pinedale and Jackson are near 20 degrees. Expect
these to quickly rise through the next several hours, as the
atmosphere continues to saturate. Otherwise, not many changes in the
forecast. A baroclinic zone is still expected to develop through the
day, setting up from Midwest to South Pass. As a result of this
zone, the area of greatest concern continues to be the I-25
Corridor, the east slopes of the Bighorn and Wind River Mountains,
the Wind River Basin and most of Natrona County. Snowfall amounts of
8 to 12 inches are still expected in the lower elevations of these
areas, with 12 to 18 inches near Barnum and Midwest and along
Highway 20/26 between Mills and Hiland in Natrona County. An
increasing threat of blowing snow will occur along Highway 20/26
this evening, leading to hazardous travel conditions. Impacts along
the I-80 Corridor remain low during the day today, as temperatures
are expected to be in the middle to upper 30s. Most of the
precipitation is also expected to occur well north of the
interstate. This is expected to change by late this afternoon toward
sunset. Winds will be turning more northerly through the night as
well.

Winter Storm Warnings and Winter Weather Advisories remain in effect
across most of the CWA through 12Z Friday morning. However, light
snow will continue to fall across central and southern portions of
the CWA through Friday morning. This additional snowfall is not
expected to cause much of an impact as snow is expected to begin to
melt during this time and through the rest of the day. An inch or
two is also expected in the mountains through the day, as weak
midlevel circulations continue over the area.

Dry conditions will be in place starting Friday night, as a ridge
begins to fold over the Northern Rockies. This ridge will be in
place through the weekend and flatten Monday as a northern stream
trough moves along the US/Canadian border. A closed low will move
over the Desert Southwest/Four Corners region Tuesday, which could
result in some showers across southern portions of Sweetwater
County. A storm system similar to todays storm could impact the
region by next Thursday/Friday. This one will bear watching and see
how it evolves through the next 7 days.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 356 PM MST Thu Mar 6 2025

The strong winter storm will continue to bring widespread impacts to
the area through much of the TAF period. Conditions will prevail at
IFR for most terminals through 06Z. LIFR conditions are possible
(60%) at times. KJAC is expected to remain mostly VFR through the
entire period with improvements to MVFR will occur overnight at
KCOD/KWRL. Frequent mountain obscuration will occur for the next 12
to 18 hours.

There will be additional improvements late in the period, after 12Z
and especially towards 17Z Friday as snow ends from west to east.
All terminals are expected to become VFR by the end of the period.

Winds continue to taper off, becoming light overnight towards Friday
morning.

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...
Winter Weather Advisory until 2 AM MST Friday for WYZ001-002-
013.

Winter Storm Warning until 5 AM MST Friday for WYZ003-005-007-
009>012-014>020-022-024>026.

Winter Weather Advisory until 5 AM MST Friday for WYZ004-006-
023-027>030.

&&

$$

UPDATE...CNJ
DISCUSSION...LaVoie
AVIATION...Hensley