419
FXUS65 KRIW 132231
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
431 PM MDT Tue May 13 2025

.KEY MESSAGES...

- Elevated to critical fire weather conditions are expected this
  afternoon for much of central and southern Wyoming.

- Strong wind gusting 45 to 55 mph is expected across portions
  of southern Wyoming, including I-80 east of Rock Springs.

- A spring system is on track to bring rain and mountain snow to
  the area this afternoon through Thursday. The highest
  precipitation totals will be across northern Wyoming.

- The warm temperatures over the past few days will continue to
  bring rises to rivers and streams as mountain snowmelt
  increases. Locations that receive precipitation may see
  further rises.

- Unsettled conditions with more seasonable temperatures are
  expected through the rest of the week. We are eyeing the
  potential for another wet system this weekend.

&&

.UPDATE...
Issued at 157 PM MDT Tue May 13 2025

The advertised low pressure system is quickly approaching Wyoming,
and we are beginning to see light precipitation push into western
areas early this afternoon. This activity will become more
widespread as it pushes east through the evening. Rain and mountain
snow will be focused most across northern areas, with a lesser
chance during this initial push across central Wyoming. The low
center is on track to move across the Yellowstone area tomorrow,
bringing more widespread precipitation during the afternoon, though
still mostly across northern and western areas. As has been the
trend for the past few days, QPF has continued to drop, likely in
response to the forecast low track drifting farther north. Finally,
we are still watching the potential for additional river level rises
given the warmth over the past few days, especially across areas
that receive precipitation through Thursday.

&&

.DISCUSSION...
Issued at 142 AM MDT Tue May 13 2025

A strong mid-level low finally pushes the ridge east Tuesday
afternoon into Tuesday night, with rain beginning across northwest
Wyoming Tuesday afternoon. Rain will become widespread Tuesday
night, becoming heavy at times across northern Wyoming. There have
been a few notable changes with this system in the past 24 hours.
Model guidance is now in good agreement that the mid-level low will
slide northeast as it passes through the area, which means most of
the precipitation will fall further north. Southern Montana will be
the beneficiary of this shift, but there will still be plentiful
snowfall (mountains) and rainfall for portions of northern Wyoming.
Precipitation will be persistent through Wednesday evening as the
majority of the weather system will pass through from Tuesday
afternoon through Wednesday evening.

Some of the most favorable locations for heavy rain are the eastern
slopes of the Absaroka Mountains (below 7500 ft) and the Cody
Foothills. Most of this rain will fall during a 12 hour period from
6 PM Tuesday through 6 AM Wednesday. If there were to be any
localized flooding it would occur in the aforementioned areas during
that 12 hour time period. At elevations above 8000 ft,
precipitation will fall as snow and the peaks of the Absaroka
Mountains will receive up to two feet of snow from this weather
system. Most elevations above 8000 ft will receive 6-12 inches
of snow, with 1-3 inches on average for YNP. Have upgraded the
Winter Storm Watches to Winter Weather Advisories. This
includes, the Absaroka Mountains and Bighorn Mountains.

Precipitation will lighten up and become less widespread Wednesday
night, but light precipitation will continue through Thursday
evening before the weather system fully exits Thursday night. Moist
unstable northwest flow will result in scattered convective showers
Thursday afternoon, with at least a 30% chance of precipitation
(highest north 80% and lowest south 30%). Beyond Thursday the
weather pattern remains somewhat unsettled with a few weak
shortwaves possible through the end of the week, but temperatures
will rebound a bit into the upper 60s east of the Divide on
Saturday. Early indications are that another potent Spring weather
system could impact the region this weekend into early next week.
This does appear to be another wet system with plenty of moisture at
its disposal.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 430 PM MDT Tue May 13 2025

VFR condition for most terminals to start the TAF period. Showers
will continue to spread across western and northern terminals this
evening and into the early morning hours Wednesday. Western
terminals will see impacts first with showers already developing
nearby. These showers will likely start moving near or over
terminals such as KJAC, KBPI, and KPNA around the start of the
period. Showers will be periodic at KPNA and KBPI through the
overnight with a lull expected around 12Z. Another round of showers
will be possible by the early afternoon on Wednesday mainly at KJAC
and KPNA. Northern terminals such as KWRL and KCOD are expected to
see prevailing rain showers this evening through Wednesday morning.
Other terminals such as KLND and KRIW may see nearby showers from
Tuesday night through Wednesday morning. Another round of afternoon
showers is possible across KCOD, KWRL, KRIW, and KLND around 19Z
Wednesday continuing into the end of the TAF period. MVFR to IFR
conditions will be possible across most terminals as a result of any
developing showers. Winds remain breezy to start the period with
most terminals seeing gusts of 20 to 30 knots. Winds begin to
decrease shortly after the start of the TAF period with lighter but
still breezy conditions through much of Wednesday. Mountain
obscuration is expected to continue to gradually spread east through
the evening into the early morning hours Wednesday. Much of the area
will see mountain obscuration through Wednesday into the end of the
TAF period.

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 from 8 PM this evening to 6 PM MDT
Wednesday for WYZ002.

Winter Weather Advisory from 4 AM to 11 PM MDT Wednesday for
WYZ008-009.

&&

$$

UPDATE...Myers
DISCUSSION...Rowe
AVIATION...Dziewaltowski