textproduct: Western and Central Wyoming

KEY MESSAGES

- Showers and thunderstorms diminish through the afternoon as drier air makes its way into the state. Best chances (40-60%) remain along and south of Interstate-80 through this evening.

- A cool night over western Wyoming, with lows in the low-to-mid 30s. Patchy frost is possible.

- Most of Monday is dry, with increasing shower and thunderstorm chances late in the day from the southwest.

UPDATE

Issued at 1224 PM MDT Sun Aug 30 2026

Isolated showers and thunderstorms are moving through the area early this afternoon. Current water vapor imagery depicts the drier air starting to make its way into western Wyoming, which will greatly limit additional shower and thunderstorm chances today. The best remaining chances (40-60%) occur over southern Wyoming, around I-80 and south, where the best moisture remains today. Some moderate to heavy rain remains possible in this area. After the last couple showers diminish this evening, dry conditions are expected overnight and into Monday morning. With a clearing sky overnight, cooler temperatures occur over western locations, with lows in the low-to- mid 30s. Some patchy frost is likely in cold prone locations, low- lying areas, and near rivers.

DISCUSSION

Issued at 236 AM MDT Sun Aug 30 2026

Another night is upon us and, once again, it is more monsoonal activity with some showers and isolated storms scattered through the area, although as I write this around 1 am most are west and south of Wyoming. These will continue through the night as well as this morning. And the main story for the next seven days will be, once again, the ebbs and flows of the monsoon, although we also have something else to talk about.

For the next 24 hours we have two concerns. The first concerns the convection. Overall, things looks somewhat less active today. Most guidance does show drier air spreading across much of the area from west to east starting this morning, but especially so this afternoon and evening as a cold front and trough move through the area. It could end up being below normal for the first time in a while across most of the area. There will still be one area of concern though, and that is largely south of a Casper to Evanston line. Moisture will linger here and so will the chance of heavy rain. Precipitable water remains around 150 percent of normal here. especially in southern Sweetwater County which has a slight risk of heavy rainfall, with a marginal chance further north. The main mitigating factor again is that there are decent low to mid level winds so the storms will be moving, so any threat of local flooding would be from training convection. Further north, the main threat from storms would shift to strong wind gusts, as we have larger dew point depressions, higher cloud bases, steep lapse rates as well as inverted V soundings. This should also be an earlier show, as most guidance shows the dry air making all the way to the southern border, and this should bring a dry period from late tonight to Monday morning. And, with the threat of heavier rain ending further north, we will likely cancel the flood watch sometime this morning.

The other concern is the coolest temperatures so far this season. There will be cooler air moving in behind the front, with lows falling into the 30s for many. The question is the concern for a frost or freeze. Temperatures have trended a bit warmer this morning. The only lower elevation locations with a greater than 2 out of 5 chance of lows below 32 degrees is the northern Jackson valley and around Bondurant. As for 28 degrees of below, the chance is less than 1 out of 4 everywhere. So, we will not issue a freeze watch at this time. If we still issued frost advisories, I would have considered one though. Just about all locations will have the coolest night they have seen in a while.

Monday should start dry. However, the monsoonal moisture will begin pushing northward again, and once again increase the chance of showers and thunderstorms, especially in southern and western Wyoming. It may take a while to arrive though, with the deepest arriving after sunset. This may limit heavy rain potential somewhat with the lack of instability, despite precipitable water values once again rising to over 150 percent at times, especially in southern Wyoming. And with southwest flow returning, warmer temperatures will returning to somewhat above normal levels.

The rest of the forecast period is again dependent on the movement of the monsoonal moisture. At this point, Tuesday looks to be more active with above normal precipitable waters and a shortwave moving through the area. Wednesday or Thursday could then be less active as drier air moves in from the west with another uptick in convection for Friday and into the weekend. However, the models have been terrible in predicting these ups and downs in the monsoonal moisture so may confidence in timing the surges of moisture is low at best. With the southwest flow continuing, temperatures will remain above normal. With the center of the ridge possibly retrograding back to the west toward next weekend, it could get quite warm again with highs in the 90s possible for the upcoming holiday weekend. So, it continues to more of the same with the monsoon continuing to dominate the weather conversation.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1125 AM MDT Sun Aug 30 2026

Primarily VFR flight conditions are expected through the period. Isolated to widely scattered showers and thunderstorms are again expected today, though less widespread than on Saturday. Brief MVFR conditions at terminals remains possible with any heavy rain. The more widespread impact potential continues to be strong outflow wind gusts of 30 to 40 knots through the day. Rain will come to an end everywhere by sunset this evening, with lighter wind and decreasing clouds through Monday morning.

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.