989
FXUS65 KRIW 150759
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
159 AM MDT Tue Oct 15 2024

.KEY MESSAGES...

- Abnormally warm and dry continue today and Wednesday.

- Increasing winds lead to near-critical fire weather conditions
  Wednesday ahead of an approaching storm.

- Much cooler temperatures and widespread rain and snow
  expected Wednesday night through Friday. Winter travel
  conditions are likely over mountain passes, especially
  Thursday night.

&&

.DISCUSSION...
Issued at 155 AM MDT Tue Oct 15 2024

Unseasonably warm and dry conditions will continue across the Cowboy
State today. Elevated to near-critical fire weather conditions
will also remain in place, however winds will remain light and keep
these conditions from becoming critical. The main issue today
will continue to be smoke from the Pack Trail wildfire.
Conditions will remain favorable for smoke from the wildfire
near Togwotee Pass to continue to drain into the Wind River
Basin and less into the Jackson Valley.

A pattern change is begin Wednesday, as a strong trough moves
onshore over the PACNW. Southwest winds, with gusts of 25 to 35
mph, will be widespread across the CWA, with the stronger gusts
occurring over the Wind Corridor (Sweetwater County to southern
Johnson County). Critical fire weather conditions are more
likely as a result, although critical RH values look to be more
isolated and confined to far northern portions of the CWA.
Regardless, the wind will be the greater threat given the dry
and unseasonably warm conditions that have been in place for the
last month or so. Will hold off on issuing a Fire Weather Watch
for now as a result. There will be a chance for showers and a
thunderstorm or two over southwestern portions of the forecast
area during the afternoon. Any shower will likely be a virga
shower, due to the boundary layer remaining very dry.

700mb temperatures will begin to cool Wednesday night into Thursday,
as the leading cold front from the PACNW trough reaches the region.
Snow levels over the western mountains will be dropping through the
night, going as low as 7500 ft by 12Z Thursday. Southwest winds will
remain gusty over the Wind Corridor, as the cold front becomes
stationary along northern and western portions of the forecast area.
There will be a chance for precipitation through the day Thursday,
with areas west of the Divide having the best chances. A second
trough will move onshore over the PACNW around 12Z Thursday and
become a focal point through the rest of the week. This trough will
dig over the Great Basin Thursday night, becoming a closed low as it
continues to dig southward over the Desert Southwest during the day
Friday. This will keep precipitation chances continuing over the
forecast area, as moisture streams northward from the east side of
the digging low. One forecast challenge we will have to keep an
eye on will be the chance for snow Friday for areas east of the
Divide. The aforementioned stationary front will push southward
Friday morning and move through the rest of the CWA through the
day. Model indications continue to show 700mb temperatures of
minus 7 to minus 9C occurring across portions of the Bighorn and
Wind River Basins after 12Z Friday. Even if snow were to fall,
any accumulations would be limited due to the relatively high
sun angle as well as the warm ground (remember how warm and dry
we`ve been lately?). Additionally, the better dynamics
associated with this storm will be well to the south. Either
way, there looks to be a good chance the CWA could see some
wetting precipitation Thursday into Friday. Any precipitation
Friday night into Saturday looks to be more isolated to widely
scattered (15 to 30%), as the closed low becomes a cutoff low
and remains over the Desert Southwest. A Freeze Watch will
likely be needed for areas east of the Divide and Sweetwater
County Friday night with temperatures dropping into the middle
to upper 20s. Conditions will be more seasonal for the weekend
as a result of this system. The low may move over the area
sometime over the weekend, however models are not indicating any
"kicker" systems at this time. Additionally, am not expecting
any considerable impacts to return if this system does return as
it will be stationary over the Four Corners region for about 24
hours and will be weaker as a result.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 939 PM MDT Mon Oct 14 2024

Light winds and a mainly cloudless sky continues through the TAF
period. Main impacts will continue to be for KJAC as wildfire smoke
from the nearby Pack Trail fire makes in into the valley. The latest
HRRR run show smoke returning to the valley in the 09Z-12Z/Tue
timeframe. Increasing smoke may reduce visibilities by or
shortly after sunrise, as has been the pattern over the last
several days. Increasing southwest flow may help to clear the
smoke somewhat during the afternoon, before additional upper-
level smoke makes its way in from a Utah fire in the evening;
there is uncertainty at this range if this smoke would cause
visibility drops.

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

&&

.FIRE WEATHER...
Issued at 156 AM MDT Tue Oct 15 2024

Elevated to near-critical fire weather conditions will continue
today. Winds will remain light, but RH values will be near
critical. Winds increase across the forecast area Wednesday,
with southwest wind gusts of 25 to 35 mph occurring for much of
the area. Near critical fire weather conditions are expected as
a result, despite RH values in the upper teens to middle 20s. A
cold front approaches the area Wednesday night into Thursday,
leading to cooler temperatures and increasing chances for
precipitation. Chances for wetting precipitation continue to
increase across much of the area Thursday and Friday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Air Quality Alert until 1 PM MDT this afternoon for WYZ012>018-
025-026.

&&

$$

DISCUSSION...LaVoie
AVIATION...Wittmann
FIRE WEATHER...LaVoie