textproduct: Western and Central Wyoming

KEY MESSAGES

- A cool and unsettled day today with periods of showers and isolated thunderstorms, with the most numerous in the afternoon and evening.

- There will be a bit of lull on Monday, with the most numerous showers across southern Wyoming.

- The chance of showers lingers through at least Wednesday and possibly through Friday. At this point, Tuesday night or Wednesday look to have the most numerous showers.

- Snow is possible at the higher elevations. Snow levels remain relatively high through Monday. The main concern for snow at pass level will be later Tuesday through Wednesday as snow levels drop.

DISCUSSION

Issued at 242 AM MDT Sun Oct 11 2026

It still looks like a rather active several days across the area. And like last night, we have some things we are fairly high confidence in and others that have more uncertainty. We will go over these below, that is why you read the discussion, of course.

Areas of showers are moving across portions of the state as I write this after midnight, with the greatest concentration of them largely across the northern half of the state. These will continue through the night as cold air over runs a cold front that has now slid down to around the Continental Divide (it went through Riverton not long ago, our wind switched to the north and the temperature dropped around 10 degrees). We will continue to showers on and off through the day, with the best coverage once again across western Wyoming. Overall, coverage of showers still looks to be the greatest today as we see the maximum impacts of the moisture streaming northward from the remnants of Tropical Storm Rachel. Overall reasoning looks similar to yesterday, with most numerous showers likely later today and into tonight as the deepest moisture moves toward the area. The deepest moisture still looks to remain west of Wyoming over eastern Idaho, but it will get close to the area. We continue to have a marginal risk of excessive rainfall across the area, this looks reasonable as there will be locally heavy rainfall. And, we have another concern this morning. Some subsidence with a possibly dry slot may develop from Sweetwater through Casper. Most models are showing 50 to 60 knots of wind at 700 millibars. The NBM ensemble gives a greater than 1 out of 2 chance of wind gusts past 55 mph across this area as well. With this we have hoisted a high wind watch from eastern Sweetwater County through Natrona County, although the best chance of high wind in Natrona County would be in western Natrona, not near Casper. Wind should decrease as the subsidence decreases toward sunrise. And, there will likely be some snow in the higher elevations, I will discuss this later in the discussion as well as rainfall amounts.

As we head into Monday, this looks to be a bit of a lull as the deeper moisture from Rachel moves away to the north and east. This is when the dominant feature becomes an upper level low that will move out of the Pacific northwest and into the Great Basin. This is where the uncertainty begins to increase. Some deterministic models as well as some ensemble members keep the low further south, dropping it further south toward southern Utah as well as Colorado. This would keep the greatest forcing and moisture further south, and any showers largely confined to southern Wyoming. The European and some other ensemble members are further north, taking the upper level low closer to the Wyoming-Colorado border which would spread better chances of showers further northward. The current forecast is somewhere in the middle, keeping most showers West of the Divide through day, then pushing deeper moisture further northward on Monday night This will be a cool day as well, with below normal temperatures across most of the area.

Tuesday looks similar, as we may be somewhat of a lull in the showers, with most activity confined to southern Wyoming. By Tuesday night, details become more uncertain. Like yesterday, the GFS remains the faster model, with the low being moved to the east, with all precipitation ending by Wednesday night. The European and some other ensemble members continue to show the upper level low cutting off the upper level low and keeping unsettled weather around through most of the week. There will likely (greater than a 2 out of 3 chance) of an area of steady precipitation across central Wyoming as a period of east to northeasterly upslope flow develops. There are still differences on exactly when this will occur (anytime from Tuesday night through Wednesday night) and the exact position of the heaviest precipitation. The chance is definitely there though. Some, we continue to be confident of a cooler and unsettled pattern. However, confidence in the details remains rather low, especially from Tuesday and beyond.

PRECIPITATION AMOUNTS...I will divide this into two periods. This first through tonight with the moisture from Rachel, and then in the period following that. Most ensemble guidance continues to show the heaviest rain across the western mountains and higher elevations, with lesser amounts further south and east. The area generally north and west of a Kemmerer to Buffalo line has at least a 1 out of 2 chance of a quarter inch of QPF or more, with most falling this afternoon and evening. The chance of an inch or more is largely restricted to the western mountains and a few adjacent valleys. The two areas with the heaviest precipitation (a greater than 1 in 2 chance of an inch and a half or more) are largely across the Wind River Range and western Yellowstone. From Monday morning through Wednesday morning, there is a north to south gradient, with the highest amounts in southern Wyoming, with lesser amounts further north and west. The 1 in 2 chance line of a quarter inch of rain or greater runs south of a Buffalo to Worland to Jackson line. The chance of inch or greater is largely in two locations, far southwestern Wyoming as well as the Wind River Range and also the southern Wind River Basin where there could be that upslope component I talked about earlier in the discussion. Additional precipitation will fall after this, but there is more uncertainty at this time.

SNOWFALL AMOUNTS...We will also talk about two different periods here. For the next 24 hours or so, two areas have the concern. One is over the Absarokas, where 700 millibar temperatures falling to around minus 2 or so, snow levels could fall down to 7000 to 7500 feet. The main concern here is that this may occur after the best moisture has moved away. The chance of 3 inches or more is generally less than 1 out of 3. The exception is near the Beartooth Highway but that is closed for the season. The other is in the Wind River Range. There is decent area of at least a 1 out of 2 chance of 6 inches or more. However, this is only at the higher elevations (above 10000 feet), so impacts will be minimal. The highest peaks may see more than a foot of new snow, but with limited impacts we decided not to issue any highlights. The second period is from Monday morning through Thursday morning. There are more concerns here. Cooler air will move on this day, with 700 millibar temperatures falling to minus 2 to minus 3 across a decent portion of the area, which would drop snow levels to 7000 to 7500 feet. This would put snow levels to pass level, especially on Tuesday night into Wednesday. There is around 1 in 3 chance of 3 inches or more of snow over some passes, like South Pass, Togwotee Pass and South Pass. There is also a much more widespread area of 6 inches of more across the Wind River Range. This looks to be the best chance of highlights, especially for the Wind River Range from Tuesday night to Wednesday. The lower elevations still look to see little or no snow. The areas of main concern are places like Cody tonight and Dubois Tuesday and into Wednesday. There could be a quick accumulation if there is enough dynamic cooling, but the chance is small, generally less than 1 out of 3.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 424 AM MDT Sun Oct 11 2026

Pacific moisture will continue to be transported into the area over the next 24 hours. A cold front now near the Continental Divide should slowly begin to lift northward into the Big Horn Basin through the day. The result is a difficult forecast with periods of rain and VFR ceilings.

Showers will be around through the morning, with a lull in the afternoon, especially across southern Wyoming and areas East of the Divide. Deeper moisture will then move in again this evening and spread further showers across the area, with the most numerous in the terminals West of the Divide as well as in vicinity of KCOD. Showers will then begin to taper off from south to north starting at around 09Z Monday as the deeper moisture moves away to the north and east. Most terminals will be MVFR ceilings at times with IFR ceilings possible at times, especially in vicinity of KCOD and KJAC. Snow levels should remain above the TAF sites. Mountain obscurations will be frequent through 12Z Monday.

Gusty wind will develop at times this afternoon and evening, especially across the southern terminals as some subsidence moves in where gusts to 25 knots are possible. The strongest wind will be in vicinity of KRKS between 01Z and 07Z Monday when gusts to 40 knots are expected with a 40 percent chance of gusts to 50 knots.

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

High Wind Watch from this evening through late tonight for WYZ019-020-030.