Jackson Hole

000
FXUS65 KRIW 151810
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1210 PM MDT Tue Sep 15 2026

.KEY MESSAGES...

- A mainly dry and seasonable day today. A few showers are
  possible in southern Wyoming after sunset and into the
  overnight hours pushing as far north as the Winds by daybreak
  Wednesday morning.

- Increasing monsoonal moisture increases the chance of showers
  starting on Wednesday, with Thursday and Friday looking like
  the most active days.

- Temperatures will remain near to above average through most 
  of the week, with a cool down likely for the weekend.

&&

.UPDATE...
Issued at 1210 PM MDT Tue Sep 15 2026

Not much a short term forecast change as IR continues to show
mainly clear skies and an empty radar through the rest of the
day. Seasonable temperatures will be on a slight warming trend
through the rest of the week into Saturday ahead of a cool down
and regime change for Sunday into early next week. Otherwise,
HiRes models continue to pump in moisture after sunset from the
south that will spread northward overnight. Isolated shower
activity and possible rumble of thunder up to the Winds by
Wednesday morning but dissipates ahead of the afternoon. More
isolated activity in the afternoon for point south of the Winds
that will spread north into Thursday and Friday being more
active, especially west of the Divide. Details uncertain on 
exact amounts, but much of the activity looks to be points west 
of the Divide and south of the Winds. Still isolated chances for
points east and north but more limited on confidence (<20-30%) 
at this time. 

&&

.DISCUSSION...
Issued at 149 AM MDT Tue Sep 15 2026

The last two nights I used music to describe the weather of the day. 
So, why not make it three days in a row. Let's step back 
another decade today, to the 60s. And let us also change music 
genres again, this time to country. And this has to with a 
pattern that you would expect more during the middle of summer, 
not a week from the start of autumn. The song is by the late, 
great Johnny Cash, Ring Of Fire. Basically, a strong ridge sets 
up in the southern United States and moisture rides along the 
northern edge of it.

There continues to be a strong ridge over the southeastern and 
south central United States, bringing more record high 
temperatures. For us in Wyoming, we will be close to the top of 
the ridge, with an increasing chance of showers. For today and 
most of tomorrow, the bulk of the moisture looks to remain to 
the south of Wyoming. Just enough moisture will creep northward 
late today and especially tonight to bring some showers to the 
southern third of the state. But these still look fairly 
isolated and even here most locations should not see one (less 
than a 1 out of 4 chance). Moisture will try to creep further 
north on Wednesday but even on this day the bulk will remain 
south of the border with only isolated activity. As for 
temperatures, today looks fairly close to normal. With southerly
flow increasing Wednesday, temperatures look warmer with highs 
rising to around 80 in some of the warmer spots.

Chances of showers should increase beginning Wednesday night and 
especially into Thursday and Friday. The ridge over the southeastern 
United States with retrograde toward the southern plains. At the 
same time, low pressure over the Pacific Northwest will begin to get 
pushed eastward. moving toward Idaho by Thursday night. This will 
push the plume of monsoonal moisture further north and west and into 
the Cowboy State. Precipitable water values could be rather high. 
The GFS has values approaching an inch, which is approaching 200 
percent of normal Wednesday night and Thursday. This model does tend 
to overcook this somewhat, so reality may be closer to 150 percent 
of normal. Nevertheless, the chance of showers and storms will 
increase. Model guidance continues to have disagreements in the 
placement of the most numerous showers though. So, we have higher 
confidence in Thursday and Friday being the two more active days, 
but placement of the most numerous showers and precipitation amounts 
remains uncertain. Temperatures will remain somewhat above normal, 
although with more cloud cover a bit cooler than on Wednesday. And 
like most monsoonal events, all areas will have a chance of a shower 
or storm, but not everyone will see one.

There is more uncertainty for the weekend. There is still a decent 
model spread on how fast the low will exit the area. Most guidance 
now takes the low north of the area across Montana. With flow 
turning northwestward, Saturday looks like a cooler day across the 
area. How fast the low moves will determine the extent of any 
precipitation though since it will be of the wrap around variety. 
Most guidance favors northern Wyoming given the position of the low, 
with lesser chances further south. Sunday looks somewhat drier 
although a few areas may still see a few showers around. Ridging 
should build back over the area to start next week, bring a return 
to dry and seasonable weather.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1059 AM MDT Tue Sep 15 2026

VFR conditions prevail through today. Winds follow typical diurnal 
trends, with some sites have 15 to 25 knot wind gusts through the 
afternoon. Moisture increases from the south overnight. KRKS is the 
greatest impacted, with rain chances starting around 06z. Any rain 
should remain south of other sites, but a few light showers or virga 
showers are possible in the vicinity of KBPI, KLND, KPNA, and KRIW 
through Wednesday morning. This push of moisture also brings a 
southerly push of wind to those aforementioned locations. Models are 
in a bit of disagreement, so confidence is not high how strong this 
southerly wind could be.

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

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...Lowe
DISCUSSION...Hattings
AVIATION...Wittmann