874
FXUS65 KRIW 030354
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
954 PM MDT Thu May 2 2024

.KEY MESSAGES...

- Breezy and dry conditions across Natrona County this afternoon,
  with a Red Flag Warning in effect through this evening.

- A quick-moving weather system will bring a round of moderate
  snow to the Wind River Range tonight into Friday morning.
  South Pass and Sinks Canyon will see accumulating snow. A
  Winter Weather Advisory is in effect tonight through Friday
  early afternoon.

- After a brief warm up this weekend, widespread rain and snow
  impact the region Monday, followed by another cooler than
  average work week.

&&

.DISCUSSION...
Issued at 250 PM MDT Thu May 2 2024

A longwave trough remains over the region today, and an embedded
shortwave will move overhead this evening. Ahead of this
shortwave weather system, dry air and breezy conditions for
central Wyoming have led to elevated fire weather concerns (see
the Fire Weather section for more details).

The shortwave weather system moving through tonight into
tomorrow (Friday) morning looks to be more robust than in
previous model runs. For this reason, snow amounts were
increased, mainly for the Wind River Range and southern
Absarokas. South Pass looks to get 4 to 6 inches of snowfall,
and although much of this may quickly compress given the
relatively strong sun leading to warm ground this late in the
spring, there were enough signals to justify issuing a
localized Winter Weather Advisory for the northeastern side of
the Wind River Range. Expect winter travel conditions over South
Pass tomorrow morning, and those in Sinks Canyon or Dubois are
likely to see a light layer of snowfall in the AM hours.

Saturday will bring a brief warm-up to the area, with
temperatures about 5 degrees above average. On Sunday, the next
weather system starts impacting the western side of the state,
bringing mountain snow, valley rain, and much cooler
temperatures. Those east of the Divide will have one more day of
warmth on Sunday with temperatures about 10 degrees above normal,
but it will come paired with strong winds gusting in the 40 to
55 mph range ahead of the cold front. Precipitation spreads east
of the Divide Sunday night, and Monday will be wet across most
of the state. Mountains could easily pick up another foot or
more of snow from this system, especially the Tetons where
multiple feet look likely (70% confidence). Lower elevations
are likely (60% chance) to see a wetting rain of a tenth or more
of precipitation, with the Bighorn and Powder River Basins
(northern Wyoming) being favored for the heavier and more
widespread rain/snow. This system exits the state Monday night.

On Tuesday and into the end of next week, cooler weather
prevails under another broad trough. Scattered mountain showers
are likely especially during the afternoons, but no other major
weather systems are set to impact the state through next Friday.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 953 PM MDT Thu May 2 2024

A weather system will pass through the Cowboy State tonight into
tomorrow. Snow is overspreading western portions of the state this
evening and this will continue moving eastward tonight into Friday
morning. Prevailing -SN and MVFR/IFR conditions tonight into early
morning for KJAC/KBPI/KPNA. Snow banding appears likely (80%), so
brief reductions to LIFR VIS possible at times, but confidence
remains low (30%) on timing and location of these bands as they move
through. A shorter period of -SN is expected at KRKS from about 10Z-
14Z/Fri. It will be quite breezy at KRKS Friday morning/afternoon
ahead of a weak cold front. A shift in wind is expected from
westerly to northeasterly early Friday evening at KRKS.

The northern edge of the -SN will be very close to KCOD early Friday
morning, so have a TEMPO for MVFR conditions due to -SN and low
clouds. For central terminals (KRIW/KLND/KCPR) -SN will begin later
tonight and persist through Friday morning. Northeasterly upslope
flow will drop CIGS to IFR at KLND/KRIW (possibly KCPR 50%) early
Friday morning, with improvement to VFR conditions Friday afternoon
as snow ends and clouds scatter out. Mountain obscuration will
become widespread tonight through Friday morning, but improvement
will occur Friday afternoon.

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

&&

.FIRE WEATHER...
Issued at 250 PM MDT Thu May 2 2024

Critical fire weather conditions currently exist across the
lower elevations of Natrona County (Fire Weather Zone 280),
with weather stations showing west winds 20 to 30 mph, gusting
35 to 45 mph. Weather models currently show these conditions
lasting until about an hour before sunset, which seems
reasonable given typical diurnal patterns. With sunset, winds
quickly decrease and RH increases. The air mass will be more
moist tomorrow with widespread light precipitation and lighter
winds, so fire weather concerns are much lower. On Sunday,
strong winds and relatively low RH in the 20 percent range could
again bring elevated fire weather concerns mainly to areas east
of the Continental Divide.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 3 PM MDT Friday for WYZ015.

&&

$$

DISCUSSION...VandenBoogart
AVIATION...Rowe
FIRE WEATHER...VandenBoogart