Mc Kinnon, Wyoming Weather Forecast Discussion

009
FXUS65 KRIW 091113
AFDRIW
Area Forecast Discussion
National Weather Service Riverton WY
513 AM MDT Tue Sep 9 2025
.KEY MESSAGES...
- Showers and thunderstorms over southwestern portions this
  morning will continue to move northeast through the day.
  Additional showers and thunderstorms will occur across the
  forecast area this afternoon and evening. Wind gusts of 35 to
  45 mph, small hail and lightning will be the main threats.
- Widespread elevated fire weather conditions are expected
  along the Rock Springs to Casper Wind Corridor through
  Thursday, with focus on stronger winds Wednesday and Thursday.
- Showers and thunderstorms will be possible Wednesday and
  Thursday, mainly over areas west of the Divide. A weather
  system will bring cooler weather to the region Friday with
  widespread precipitation Friday afternoon and Friday night.
  Chances for showers and isolated thunderstorms return
  Saturday.
&&
.DISCUSSION...
Issued at 120 AM MDT Tue Sep 9 2025
An upper level low has moved onshore near the CA/OR border earlier
Monday evening and is expected to dig southward over northern CA
through the day today. This will cause a ridge axis over the Cowboy
State to amplify and gradually shift eastward through the day. This
eastward shift will allow the winds aloft to turn more
southwesterly. Showers and thunderstorms over portions of UT will
continue to move toward the northeast and look to reach southern
Lincoln County and the Flaming Gorge area around 09Z. These showers
will continue to trek northeast across the Upper Green River Basin
and portions of Sweetwater County through the rest of the morning.
Little to no impacts are expected, other than isolated lightning
strikes. Additional showers and thunderstorms will be widely
scattered (20-30% chance) across the forecast area this afternoon,
as additional shortwaves move over the area. The Absaroka and
northern end of the Wind River Mountains, as well as the Cody
Foothills, will have the better chances. The showers and storms from
these areas will move over the Bighorn Basin this evening through
06Z Wednesday. Wind gusts of 35 to 45 mph, small hail and lightning
will be the main threats. Any smoke that made its way into the
forecast area Monday will once again get pushed northward out of the
area through the day.
This overall pattern will continue Wednesday and Thursday, as the
upper level low slowly rotates over portions of OR, CA, NV and ID.
The southwest flow aloft will continue over the Cowboy State, as a
high develops over the TX Panhandle and strengthens the ridge over
the Plains. These winds will usher in more drier air once again and
set up a pseudo-dryline over eastern portions of Johnson/Natrona
counties Wednesday afternoon. Any convection looks to be confined to
western portions of the state along and west of a Kemmerer-to-Cody
line and be widely scattered (20% chance) through the afternoon and
overnight hours. Elevated fire weather conditions will be in place
Wednesday and Thursday, with gusts up to 30 mph each afternoon. RH
values are expected to stay above critical thresholds (15%), but
will still be low in the 18 to 25% range. Showers and thunderstorms
will once again develop across areas west of the Divide Thursday
afternoon, as a leeside low develops over southern MT and the
associated cold front leads to the convection over western portions.
Wind gusts of 40 to 55 mph, small hail and lightning will be the
main threats through the afternoon and evening.
Isolated showers will remain possible over western portions Thursday
night into Friday morning, as the eastern fringes of the upper low
approach. Temperatures will be 5 to 10 degrees cooler Friday, as a
result of this low. Cloud cover will certainly aid in these cooler
temperatures. Precipitation chances will quickly increase over much
of the CWA Friday afternoon, as a portion of the low rounds the base
of the trough and moves northward. Precipitation will continue
through the overnight hours, as the low moves over southern and
eastern portions of MT by 12Z Saturday. Precipitation chances will
be varied Saturday, as the low stays in MT and a trough rotates
around the low and moves eastward over the forecast area.
Temperatures will remain on the cool side with highs in the 60s west
of the Divide and lower to middle 70s east of the Divide. Freezing
temperatures could occur for portions west of the Divide Friday and
Saturday nights in the more cold prone locations, like Cokeville and
Bondurant. Sunday looks to remain mainly dry and seasonal, with
isolated showers and storms possible over far southwestern portions
late in the afternoon.
&&
.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 512 AM MDT Tue Sep 9 2025
VFR conditions are expected to prevail through much of the TAF
period across all terminals. This morning a line of showers and
thunderstorms is making its way across southwestern WY. As a result
TEMPO groups have been added to KPNA and KBPI due to the chance
for a brief shower or thunderstorm to start the period. A brief
increase in winds may accompany these showers and thunderstorms
with gusts near 25 knots possible. Precipitation should move
out by 15Z if not earlier at these terminals. This line may
remain intact as it nears KLND but chances are slim around 20%.
Showers and thunderstorms look to redevelop by the late afternoon
with all terminals having a chance of a brief shower or storm. The
best chances look to be at KJAC, KPNA, and KBPI with KCOD and KLND
having slightly less of a chance. Precipitation gradually spreads
east through the evening with terminals east of the Divide seeing
precipitation chances increase around sunset. Gusty winds of 20 to
30 knots may accompany any developing showers or storms.
Precipitation gradually dissipates through the overnight hours with
SCT-BKN 100-150 cloud decks lingering into the end of the TAF
period. Mountain obscuration will be possible periodically
throughout the TAF period as showers and storms move through.
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...LaVoie
AVIATION...Dziewaltowski

NWS RIW Office Area Forecast Discussion