538
FXUS65 KRIW 091911
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1211 PM MST Sat Nov 9 2024

.KEY MESSAGES...

- Seasonably cool and mostly dry today. Light rain
  showers/drizzle remain possible (30%) in southeast Natrona
  County through this afternoon before shifting east this
  evening.

- A warmup will occur Sunday and Monday, with much of the area
  rising into the 50s!

- There is a moderate chance (30-40% chance) for snow in
  northwestern WY Sunday afternoon.

- Next consequential weather system brings impacts to WY late
  Monday through Tuesday night. Snow showers linger across
  northwest WY through next week.

&&

.DISCUSSION...
Issued at 1207 PM MST Sat Nov 9 2024

The warming trend will continue through this weekend as high
pressure keeps it clear/dry for most of the area after this
afternoon. High temps look to rise into the low 50s east of the
Continental Divide/middle 40s west of the Continental Divide by
Sunday, and Monday temps look to be similar. Model guidance has a
weak, quick-hitting shortwave on Sunday/Sunday night. This shortwave
has a chance (The NBM has probs of 20-40% for 0.1" of QPF) of
bringing snow to northwestern WY mountains and YNP. The timing of
this shortwave has come into focus, with the time period of light
snow being mainly Sunday afternoon/evening. A ridge will build back
in after this shortwave passes through, so temps won`t change much
until early next week with the next impactful weather system.

There is now high confidence in the timing of a large trough pushing
into the area from the west late Monday into Tuesday. Wind will
increase ahead of this weather system on Monday into Tuesday with
southwesterly flow developing and tightening of the pressure
gradient. This is not looking like a high wind scenario/event even
where the strongest wind occurs (NBM probs have the chance for
greater than 50 mph wind gusts at around 5-10% for southern Natrona
County), so while there is a low chance of wind gusts above 50 mph
it is not the favored outcome. There will be widespread gusts of 15
to 25 mph and gusts of 25 to 35 mph along the Wind corridor from
Eastern Sweetwater County up into southern Johnson County Monday
afternoon. Wind will increase Monday night along the Wind Corridor,
with gusts of 30-40 mph (higher gusts to 50 mph at the higher
elevations) as the trough approaches the area. As the trough pushes
through on Tuesday wind will increase across the area, with gusts of
20-40 mph through Tuesday afternoon.

Model guidance is in good agreement that this will be an open wave
trough that progresses quickly from west to east across the region.
With this type of weather system western WY predominantly takes the
brunt of the precip, with lee side mountain shadowing preventing
much precip from occurring east of the Continental Divide. NBM probs
for 48 hour precip (QPF) greater than 0.1" for lower elevations east
of the Continental Divide are 30% and less from Monday night through
Tuesday night. Overall the trend is for lower precip (QPF) amounts
across the area with this weather system. Now for western mountains
the NBM probs for 48 hour precip (QPF) greater than 0.5" are in the
20-40% range for most mountain locations. There is a higher chance
(70-80%) on the Pitchstone Plateau where upslope is favored. As
previously mentioned, this weather system appears to be progressive
in nature and while it will very likely (90%) bring colder temps
back to WY for a few days it will take the cold air with it as it
leaves as a ridge develops behind it for the latter half of the
week. Another trough looks to come in from the west next weekend and
right now it looks like it will provide a better chance for
widespread precip chances.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1025 AM MST Sat Nov 9 2024

A large scale storm system is currently centered over central
Nebraska, rotating clouds from eastern WY southwest over the
eastern parts of the forecast area. Low- and mid-level clouds
around KCPR will slowly rise and move southeast during the
afternoon, with high clouds along with outer edge of the system.
Some fog in Jackson Hole brought KJAC down to IFR for a couple
hours this morning, but it is dissipating late in the morning
with clear skies expected for most of the afternoon. VFR
conditions are expected at all TAF sites through the forecast
period. The high clouds over central WY will move eastward this
afternoon with the storm system, with clear skies on the
backside. Breezy and gusty winds will continue this afternoon at
KRKS, with around 10kt NW wind at KCPR, KBPI, and KPNA.

The flow pattern shifts to more westerly overnight, bringing
high then mid-level clouds over northwest WY Sunday morning.
Winds will increase again between 10/16-18Z at KRKS and KCPR,
with some gusty southwest-west winds also developing around
10/18Z at KCOD and KJAC. A slight chance of showers will be over
the northwest mountains Sunday afternoon, but weak high pressure
will keep moisture more to the north. Breezy winds are possible
Sunday night into Monday morning as a system approaches from the
west late Monday.

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...
None.

&&

$$

DISCUSSION...Rowe
AVIATION...McDonald