textproduct: Western and Central Wyoming

KEY MESSAGES

- Scattered rain showers continue into the overnight hours, with gusty outflow winds up to 40 to 50 mph the main hazard. The heaviest precipitation looks to arrive Sunday through Monday, with locally heavy rain possible, especially for the western mountains.

- Cooler temperatures move in starting Sunday. Several inches of snow are likely (a greater than 1 in 2 chance) in the mountains above 10000 feet.

- Strong gusty winds (50+ mph) may be possible late Sunday into Monday, mainly across central and southern WY from Casper to Rock Springs.

- Periods of showers will continue through the weekend, although details of rainfall amount and placement of heaviest rain remains uncertain, especially from Tuesday and beyond.

UPDATE

Issued at 1158 AM MDT Sat Oct 10 2026

A few things to update regarding the near term forecast as models have begun to come into better agreement. Starting with the remainder of Saturday, temperatures are looking to be on the warmer side especially east of the Divide. Southwesterly winds have already begun to warm temperatures into the 70s across many locations east of the Divide. Highs are forecast to get into the upper 70s to low 80s east of the Divide with the Bighorn Basin being the cooler location. West of the Divide, highs look to get into the mid 50s to low 60s. Winds will be gusty throughout the day with speeds of 15 to 25 mph and periodic gusts of 30 to 40 mph. Weaker winds are expected over northern and western WY. The focus now turns towards the start of a prolonged period of unsettled weather as multiple systems interact and move through the region over the next few days.

Showers have already begun to develop and move into portions of western WY this morning. Due to some breaks in the cloud cover a few thunderstorms cannot be ruled out this afternoon and evening. The best chances look to be across western and southwestern WY where the best dynamics are likely to occur. The biggest concern with any thunderstorms would be strong gusty outflow winds, some small hail and moderate to heavy rainfall. As mentioned earlier there are a few adjustments to the forecast, as a result of hi-res models starting to ingest data. The first is less precipitation amounts east of the Divide due to downsloping and a shift farther west in the storm track. This shift will lead to heavier precipitation remaining over western WY and only periodic round of showers east of the Divide. Any prevailing period of precipitation is looking less likely east of the Divide, which will lead to lower rainfall amounts. The other forecast adjustment is temperatures which have trended warmer not only across lower elevations but the higher elevations as well. 700 mb temperatures are warmer than they were only 24 hours ago with values now at 2 to 5C which would keep snow levels above 10,000 feet and possibly higher. Northern portions of the Absarokas and YNP may see colder temperatures leading to better chances for accumulating snowfall across the highest elevations. As for the lower elevations, the shift in temperatures mainly impacts the Bighorn Basin as models show the coldest sfc lvl temperatures struggling to make it far south. While cold temperatures near freezing are still possible for the Bighorn Basin, they seem to be delayed further into Sunday night and Monday morning. The degree of cold is also less with lows forecast to not be as drastic as thought only a day ago. Due to this uncertainty, any freeze related products are going to be held off for now. The best chances look to be Sunday night into Monday morning with much of the basin having a 30-60% chance for lows of 32F or less. These warmer temperatures have also led to lower chances for any wintry precipitation mixing in but that occurring in some isolated locations till cannot be ruled out. The last adjustment is increasing winds especially for Sunday night into Monday, mainly across portions of central and southern WY. Models are showing a rather potent jet with 700 mb winds of 50 to 65 knots move across the Wind Corridor from Casper to Rock Springs. Probabilistic guidance is showing a large swath of 30-50% for wind gusts exceeding 50 mph Sunday night through much of Monday. So this will be worth monitoring as there could be the need for some high wind highlights if winds are forecast to gust this high.

DISCUSSION

Issued at 250 AM MDT Sat Oct 10 2026

Being a member of Gen X, I was the first generation to watch Sesame Street when I was a wee lad many eons ago. And at the end, right before the closing credits, they always said the episode was sponsored by two letters. Well, this Area Forecast Discussion is sponsored by the letters T and U. T stands for transition, as we move from the warm and dry pattern into a cooler and wetter one. And U is for uncertainty, as are still a fair amount of questions with the forecast, especially in regards to the snowfall potential at the lower elevations and details of the forecast toward the middle and end of next week.

The T for transition will be today. We had a few showers yesterday, and radar shows more showers, generally of the light variety moving from Idaho and Utah with the first hits of moisture. The players in the forecast remain the same, a cold front dropping in from Montana, an upper level low and associated trough dropping in from the Pacific Northwest and Tropical Storm Rachel. The cold front should remain largely north of the border today, so we will likely have one more warm day today, maybe the warmest for the rest of the calendar year. Some warmer spots will likely see another high in the 90s. We will also have continued gusty wind in the favored southwest flow locations from Rock Springs to southern Johnson County. As for showers, moisture from Rachel will increase through the day, drawn northward by the trough. The best chance of showers and storms will be largely West of the Divide today as downsloping flow should limit shower East of the Divide through the daylight hours. There will still be some, but not as numerous as West of the Divide. And there will likely be some thunderstorms today, as there is decent CAPE for October, up to 300 J/Kg with lifted indices down to minus 2. Coverage of showers looks to increase tonight as deeper moisture moves northward and some jet energy moves into the area, increasing upper level divergence.

The wettest day still looks to be Sunday, as the deepest moisture from Rachel moves across the area. Reasoning today is fairly similar to yesterday. There will be locally heavy rain. Precipitable water values could be as high as 0.75 inches, which is close to 200 percent of the mean and could be a daily record for Sunday. The jet will also be nearby, keeping upper level divergence around. Again, the placement of the heaviest precipitation will be across western Wyoming, with decreasing chances and amounts further to the east. I will discuss potential amounts later in the discussion. I did give some consideration to flood watches, but decided against them for now for the following reasons. One, it has been very dry over the past couple of weeks, so there is decent amount of room in the soil to soak up some of the rain. Two, the cold front will be further south today, and instability will be limited. So, precipitation looks more stratiform than convective, which should limit precipitation rates somewhat. Three, some of the highest elevations may be seeing snow at this point, limiting runoff. I will discuss snowfall mounts later in the discussion as well. And four, most deterministic models and a majority of the ensemble members show the best QPF remaining west of Wyoming. The area I would be most concerned about would be the western slopes of the Wind River Range with the upslope flow, the Tetons as well as Yellowstone Park. We still have time to decide though as the heaviest rain wouldn't be until Sunday, with most guidance zeroing in between noon and late Sunday night, with some decrease after that as the deepest moisture from Rachel moves away to the north and east.

By Monday, the dominant feature will be the Upper Level which by this point will begin to turn eastward toward the Rockies. Most guidance shows lighter precipitation Monday afternoon, and most confined to areas West of the Divide by that time, with only lighter amounts East, Most will also be confined to southern Wyoming, with northern Wyoming largely dry.

We will now discuss precipitation amounts, I will reference from Saturday night through Monday, when the most rain is expected to fall. The vast majority of the area has at least a 1 in 2 chance of a quarter of an inch or precipitation or more, with the smallest chance south and east of a Rock Springs to Casper line. Chances of an inch or more (greater than 1 in 4 chance) are largely confined the northwestern Wyoming as well as the Bighorns where there will be an upslope component. The areas with a greater than 2 inches of precipitation, which is where the best chance of excessive rainfall would be is in western Yellowstone Park, the Tetons and the Wind River Range. However, some of this precipitation over the higher elevations will likely fall in the form of snow, especially Sunday through Monday when the cooler air moves out of Montana. Additional rainfall will occur Monday night but amounts look lighter at this time.

And now we will focus on the frozen form of precipitation, snow. With warmer air remaining over the area today, any snow would be restricted to the highest elevations, above 11000 feet for the most part. Cooler air begins to ooze into the area Saturday night and especially Sunday, lowering snow levels. Levels bottom out late Sunday into Sunday night. Across Central Wyoming, with 700 millibar temperatures bottoming out between plus 1 to plus 3, this should keep snow levels above 9000 feet, above most passes, Togwotee Pass could see some wet snow, but any impacts should be minimal. As for highlights, we have held off for now. Looking at the NBM ensemble 72 hour snowfall through 6 am on Tuesday the areas that have a greater than 1 in 2 chance of six inches or more are largely restricted to portions of the Absarokas and the Wind River Range, largely above 10000 to 11000 feet. Portions of the Wind River Range will almost certainly get at least a foot of snow, and possibly over two feet of new snow. However, this would only be at the highest elevations where impacts would be very limited. We will let the day shift take another look. In the lower elevations, the main area of concern would be northern Park County, where 700 millibar temperatures will be the coolest. The question that remains is will there be enough dynamic cooling to cool temperatures at the surface enough. Ensembles only give a 1 in 5 chance of an inch or more here, but model performance in this area is poor and we still have a decent setup with the overrunning moisture and the jet nearby. It wouldn't be until Sunday or Sunday night so there is still time to take another look but this has to be watched.

And following this is where the U for uncertainty comes in. And it has to do with the progress of the upper level low, as guidance has vastly different solutions with it. Tuesday has some agreement with showery weather during the day and possibly more at night as deeper moisture moves toward the area. Following this is were there is a large amount of divergence. The GFS as well as some ensemble members pick up the upper level low and move it quickly across the state getting kicked by a trough moving across the US-Candian border, bringing a wet Wednesday then moving it out of the area for later in the week for a return to drier weather. The European has the upper level low missing the connection and getting blocked by a building ridge to the west, cutting the low off over the Great Basin and keeping potentially unsettled weather into the end of the week. Confidence is very low on which will happen at this time though. So, there it is a (very long) Area Forecast Discussion brought to you by the letters T and U.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 949 PM MDT Sat Oct 10 2026

A large weather system with plenty of moisture will impact the area over the next 24 hours and beyond. A cold front will push south through the area tonight stalling along the Continental Divide and then retreating northward into the Bighorn Basin Sunday morning. All terminals will drop to MVFR due to low CIGS, reduced VIS from rain, or a combination of both.

A relative lull in rain coverage will occur Sunday afternoon before more convective showers move into southern portions of the area late afternoon into Sunday evening. There will be some isolated storms as well Sunday afternoon and evening. This lull may lead to slightly improved conditions for much of Sunday afternoon for most terminals. KCOD will drop to IFR CIGS by around 08Z and remain IFR through much of Sunday afternoon. It may improve to low MVFR at KCOD late Sunday afternoon through Sunday evening, but CIGS will be right around FL010. Precipitation should remain rain at all terminals through the TAF period.

Wind will be quite breezy, especially Sunday afternoon and evening. As stronger wind moves in aloft wind may increase more Sunday evening into Sunday night. For northern terminals (KCOD, KWRL) wind will remain northerly with the cold front south of the terminals. For other terminals wind will generally be from the south through the TAF period. Frequent mountain obscuration through the TAF period.

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.