textproduct: Western and Central Wyoming

KEY MESSAGES

- A weather system moving through the region keeps it cool and mostly cloudy conditions tonight.

- Tonight's precipitation will be focused over the mountains and western valleys, but basins in central and northern Wyoming will see hit- or- miss scattered showers as well. - Accumulating snow is likely in the higher elevation mountains tonight through Sunday, mainly above 10000 to 11000 feet.

- After the current weather system exits Sunday night, dry conditions prevail with temperatures gradually warming up over the first half of the work week.

UPDATE

Issued at 915 AM MDT Sat May 30 2026

No major changes to the forecast today after looking through 12Z high-resolution model guidance. My esteemed colleague articulated the evolution of the current system well in the Discussion section below, and this overall thinking holds.

Highlighting a few items here: Central Wyoming basins look to remain mostly dry during the daytime hours today, with only isolated showers and perhaps a few thunderstorms, while most of today's moisture falls over southwestern Wyoming and over the mountains in the form of snow above about 10000 ft. 12Z model guidance highlights the Bighorn Mountains, Johnson County, and the greater Powder River Basin as having decent (80%) chances for more numerous showers and overnight thunderstorms as the core of the upper low rotates through that area. Thunderstorms are not expected to be strong, but are notable for being outside of their usual 2 PM to 7 PM diurnally normal occurrence window, thanks largely to cold air aloft creating some instability without the help of solar surface heating. For the system as a whole, forecast precipitation amounts have trended down slightly, but many locations will still receive a pleasant late Spring soak.

DISCUSSION

Issued at 144 AM MDT Sat May 30 2026

Showers will continue to increase early this morning as the upper level low approaches, mainly occurring over western and southern portions. A sfc reflection of the low will develop near La Barge/Farson by mid-morning and track to the northeast over the Divide and into the Wind River Basin through the rest of the morning into the early afternoon. Showers will rotate to the northwest during this time, with showers being roughly confined along and west of a Cody-to-Rock Springs line. Dewpoints will drop into the middle 30s over Natrona County, eastern portions of Fremont County, far southern portions of the Bighorn Basin and Johnson County by 21Z as a result of southerly winds shunting the available moisture northward. Most areas east of the Divide are likely to stay dry during the afternoon. Northern portions of the Bighorn Basin and Johnson County will be the exceptions, with Johnson County having the higher chances. A boundary will be in place that could provide a trigger for any shower/storm to develop in this area, but will quickly move northward due to the aforementioned southerly winds pushing the boundary northward. The potential for any strong storm will be in this area, with forecasted CAPE values of 1000-1500 J/kg and LI values < -6. Shear will not be strong, so instability will be the main driver for any severe storm. Otherwise, isolated to scattered thunderstorms will be embedded within the aforementioned shower activity over the west this afternoon.

The upper level low will slowly track over the Cowboy State through the overnight hours tonight, reaching the northeast corner of the state by 12Z Sunday. Showers and will continue over western portions and Sweetwater County early in the evening, with additional showers developing over the Bighorn and Wind River Basins after 06Z on the backside of the low. Showers will increasingly become confined over northern portions after 12Z Sunday as the upper low continues its progression over eastern MT/the western Dakotas through the day. Winds will increase across the CWA Sunday, as the gradient tightens in the wake of the departing low. Gusts of 25 to 35 mph will occur through much of the day, quickly decreasing through the evening.

Rainfall amounts over 0.10" from today through Sunday are still forecasted to occur along and north of a Kemmerer-to-Riverton- to-Kaycee line, with far southwestern portions of Sweetwater County included. The heaviest amounts of 0.75 to 1" are still expected over northern and northwestern portions of the CWA. Flooding or rain-on-snow is not expected from this event, as most snow in the 9000 to 10000ft range (SnoTel sites) is gone already.

Isolated showers and thunderstorms will be possible Monday, as a shortwave moves over the Cowboy State. Winds aloft will be southwesterly as a trough develops over the Northern Rockies from the remnants of today's upper low. Most of the convection looks to develop over the western mountains between 19Z and 21Z and quickly push eastward over areas east of the Divide and Sweetwater County. Additional showers will move over northwestern and northern portions late in the afternoon into the evening, as a second shortwave rotates through the base of the trough. Tuesday looks to stay mainly dry, with west-southwest winds aloft keeping any potential convection over far eastern portions of the state. Showers and thunderstorms will be possible again Wednesday and Thursday, with dry conditions returning for Friday. Temperatures will be above normal these days, with highs in the upper 70s into the 80s.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 517 PM MDT Sat May 30 2026

Scattered showers and thunderstorms will be ongoing across much of Wyoming from the start of the TAF period into the overnight hours. There is higher confidence (40 to 60 percent) that KJAC, KCOD, and KPNA will have shower and/or thunderstorm potential through at least the first half of the TAF period. Shower and thunderstorm potential should largely come to an end, at the latest, by 05Z/06Z at KRKS, KRIW, KLND, and KBPI. There is a 30 percent chance of light rain moving into KRIW, KBPI, and KLND overnight. Rain showers arrive at KWRL around sunrise Sunday and persist the remainder of the period. Thunderstorms are possible (30 percent) again late in the TAF period at KCPR, KCOD, and KWRL. MVFR to IFR flight conditions are possible in any shower or thunderstorm.

Expect wind to range from 5kts to 15kts this TAF period, with wind gusts of 20kts to 30kts at most terminals. The exception terminals are KWRL and KJAC, where frequent gusts are not forecast. However, gusty and erratic winds are possible in and around any thunderstorm. Mountain obscurations will be common through at least 18Z, especially around showers and thunderstorms.

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.