textproduct: Western and Central Wyoming

KEY MESSAGES

- The first of a series of cold fronts has made it to the Continental Divide today, which will keep it cooler this afternoon. Scattered rain showers and thunderstorms will develop this afternoon, with more widespread precipitation tonight.

- Weather system brings widespread rain and snow tonight through Tuesday evening, mainly for central and southern portions of the area.

- Winter Weather Advisories have been issued for the eastern slopes of the Wind River Mountains and Bighorn Mountains, mainly for South Pass and Powder River Pass.

- Freeze Watches remain in effect for Tuesday night into Wednesday morning, with widespread temperatures between 20 and 30 degrees.

UPDATE

Issued at 121 PM MDT Mon May 4 2026

Scattered rain showers and thunderstorms will develop and move through the area this afternoon transitioning to more of a widespread rain or snow from central to southern portions of the area. Thunderstorms should be weak today, so only some small hail, gusty wind, and heavy rain will be threats. The precipitation forecast for tonight through Tuesday night remains difficult due to many competing factors. There is better consensus on the timing of the second cold front making it to the Continental Divide by sunrise Tuesday and pushing southwest through Sweetwater and Lincoln County before noon. This secondary cold front will bring much cooler air aloft and result in a changeover to all snow once it passes through. There may be a mix of rain and snow Tuesday afternoon for lower elevations due to some daytime surface heating, but dropped high temperatures for Tuesday, because thick cloud cover combined with falling snow will really mitigate most of the daytime heating. Increased precipitation amounts for the Wind River Basin as well as Natrona County where favorable jet dynamics combined with upslope flow will likely (60-70%) lead to more precipitation than model guidance is depicting. Snow amounts are only a trace to 4 inches for lower elevations due to a good portion of the precipitation falling during the day on Tuesday. The May sun angle combined with temperatures in the mid to upper 30s will greatly limit snowfall accumulations during the day on Tuesday. Locations with the highest impacts from snow tonight through Tuesday evening will be Powder River Pass, South Pass, Beaver Rim and Jeffrey City, Lander, and along US 20/26 from Moneta to Natrona.

The Freeze Watches remain in effect for Tuesday night into Wednesday morning, with widespread low temperatures from 20 F to 30 F across lower elevations. A warmup will occur Thursday and Friday, with slightly cooler temperatures and more precipitation chances this weekend. Next week looks much warmer and could put an end to any potential for winter weather this season for lower elevations.

DISCUSSION

Issued at 200 AM MDT Mon May 4 2026

IR currently depicts a closed low to the southwest near California as WV shows the PFJ dipping further south out of Canada and Montana into northeastern portions of the state. Current model trends continue the southward progression of the jet with a jet max of 120kts pushing into the next shortwave expanding across much of the CWA for Monday. This will drop a cold front through the area in the morning hours that will see cooler temperatures from Sunday around 10 to 15 degrees for afternoon highs. Otherwise, scattered rain showers expected with the front that will expand into the evening and overnight hours as the shortwave progressively moves across the CWA. Minimal impacts expected with any snow accumulations constrained to higher elevations even above mountain passes.

Tuesday will see a more widespread mountain snow/valley rain effect as the aforementioned low to the southwest will embed into the positively tilted trough extending from the Dakotas. More ample divergence aloft expected, especially across the southern half of the CWA where QPF amounts could push over a quarter inch (60-70%) in some spots along the I-80 corridor of Sweetwater County and points south to the Colorado border. Otherwise, snowfall rates for the higher elevations will be greatest during the afternoon and into the evening hours. Minimal impacts expected to mountain passes (South Pass the only one to push advisory level amounts). However, with the warm temperatures ahead of this system and more of a longer duration time frame, any issuances were held off at this time for Tuesday and Tuesday night. However, a reinforcement of cooler air expected into Wednesday morning seeing a widespread below freezing event for basins east of the Divide. As such, freeze watches continue with this being the coldest morning of the week ahead.

Additional precipitation chances with minimal impacts expected Thursday and Thursday night as the main trough exits to the east. This will give way to upper level ridging to build back in Friday and into the weekend with dry conditions and a warming trend expected. Northwest flow aloft extends through into early next week with a minor shortwave pushing to the northeast Saturday afternoon that might see some sporadic showers for the Bighorns and northeastern counties, but much of the activity will remain northeast.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 351 PM MDT Mon May 4 2026

A cold front drops down from the north overnight, bringing colder temperatures and precipitation chances. To start the period, between 00z and 12z, it is a difficult forecast due to the complex transition of evening showers ending, widespread precipitation starting, the front moving through, and when/if a transition from rain to any snow occurs. For most locations, precipitation continues through the end of the period once it begins this evening or overnight. KCOD, KJAC, and KWRL would be the least favored for this continuous precipitation. A period of heavier snow/rain looks to occur around KCPR, KLND, and KRIW Tuesday afternoon.

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

Freeze Watch from late Tuesday night through Wednesday morning for WYZ003>006-010-011-017-018-020.

Winter Weather Advisory from 1 AM Tuesday to 1 AM MDT Wednesday for WYZ009-015.