textproduct: Western and Central Wyoming

KEY MESSAGES

- Warm and breezy today, with elevated to near critical fire weather conditions. A few showers or storms are possible (15 to 40 percent) from about Rock Springs to Buffalo through this evening.

- A potent weather system brings rain Sunday afternoon, which transitions to snow (for all elevations) Sunday night into Monday morning. Strong north winds, freezing temperatures, and accumulating snow will create poor travel conditions for portions of the area Sunday night through at least midday Monday. Some uncertainty still exists when it comes to snow amounts.

UPDATE

Issued at 1237 PM MDT Sat May 16 2026

Updates to winter highlights are the main focus with today's update. Considerations for the Winter Storm Warnings and Winter Weather Advisories were snow amounts, strong winds, and it being mid- May. This looks to be an unusual late season snow event for central and southern Wyoming, so a push towards highlights were given. Focus remains on the Monday morning commute, which could be icy, slushy, and snowy for a large portion of central and southern Wyoming. There will also be strong north winds, contributing further to winter travel conditions. Highest impacted areas currently look to be around South Pass and I-80 east of Rock Springs. Another area of concern could be Highway 20/26 between Shoshoni and Casper as snow totals increase with higher elevations. The big caveat to all this is still the uncertainty with the exact track of the weather system; a more southward solution would lessen amounts, while a northern shift would increase them. Temperatures will also influence when rain transitions to snow and if freezing of surfaces will be allowed earlier. An earlier transition to snow will aid in freezing ground and accumulating snow.

DISCUSSION

Issued at 259 AM MDT Sat May 16 2026

Before I came to work tonight, I was watching one of my favorite 80s movies, Back To The Future. And the song over the closing credits reminds me of the weather pattern over the few days. That song is "Back In Time" by Huey Lewis and the News. It has felt more like June the past several days, but we will be going back in time to feel more like March for a couple of days starting on Sunday.

We will have one more day that has been similar to the last several. That means another day of above normal temperatures, a gusty wind and low humidity. The result will be another day of elevated to locally critical fire weather across the area. Increasing mid level moisture may bring a stray shower this afternoon or evening, mainly across the northwest and from Sweetwater to Natrona County, but most areas will not see one. With the still large dew point depressions through, there would be strong wind gusts out of any shower or storm.

And then we begin to snap back toward March as an upper level low moves out of the Pacific northwest, opens into a trough and moves toward and through Wyoming from Sunday into Monday, bringing some rain later Sunday that will likely change to snow on Sunday evening. Some details have come into better agreement, but others are still in flux. Timing has come into better agreement, with the maximum impacts expected Sunday night and into the first part of Monday, with most impacts ending Monday evening. Most guidance also puts the heaviest QPF over the southern and eastern portions of the area, with a generally lessening in amounts the further north and west you go. And with flow turning northeast, amounts look heaviest in the northeast upslope locations like Casper, Lander, and Jeffrey City.

However, there are still a few things in flux. For one, how close will a 700 millibar circulation get to Wyoming. Some ensemble members, as well as the European model, bring somewhat more moisture into out area, mainly in Sweetwater, Natrona, and eastern Fremont Counties. It also brings more moisture further northward into the Bighorn Basin. Meanwhile, other members, and the GFS, keep the circulation a bit further south and as a result, brings in less QPF.

Then we have the impact of the time of year. It is mid May, and we are less than five weeks from the summer solstice. This means the sun will be very strong. As a result, a majority of the accumulation, and road impacts, would occur on Sunday night, as snow would have trouble accumulating during the day. In addition, the ground is warm given the stretch of record breaking warmth we had much of last week. Much of the snow that falls would initially melt as it falls, especially on paved surfaces. Snowfall rates will be critical in this situation. If they are heavy enough, it could overcome the warm ground and accumulate on roads and possibly ice them over, bringing travel impacts, with the maximum impact expected between 9 pm Sunday and 9 am Monday. Following that, snow should gradually melt on roads as the sun becomes stronger. As a result, official accumulations may not be what people see in their yards and fields. And finally, we have to factor in elevation, as a few hundred feet of elevation or a degree or two will make a big difference in accumulation.

There is one more factor to consider though, and that is wind. As lee cyclogenesis occurs over Colorado, the pressure gradient will tighten across the area, especially so across Sweetwater County and portions of the Bighorn Basin. Ensembles are giving a greater than 2 out of 5 chance of wind gusts past 50 mph in these locations. I'm not as concerned about the Big Horn Basin, as snow should be lighter here. Of greater concern is Sweetwater County, as Interstate 80 could be a mess in this situation. The wind would be strongest later Sunday night and Monday morning, decreasing Monday afternoon as the low moves away to the east.

So, finally what everyone is wondering. How much snow will we get? Most of the area, with the exception of the eastern Bighorn due to northeasterly downslope as well as some of the western valleys, have at least a 2 out of 3 chance of an inch or more. When we go up to a 1 out of 2 chance of 3 inches or more, this includes places like Lander as well as most of Natrona County as well as Sweetwater County to the east of Rock Springs. The chance of over 6 inches is rather elevation dependent, largely above 6000 feet in elevation. This includes much of the Green and Rattlesnake Range, so we will hoist a Winter Storm Watch for this zone. We will also include one for the eastern Wind River Range where snow and wind may make South Pass rather difficult to travel, as well as Casper Mountain to match up with neighboring offices. Thought about one for eastern Sweetwater County as well, but will punt for now.

The heaviest snow should end by Monday evening. However, lingering moisture and cyclonic curvature over Wyoming will keep things unsettled through Tuesday and Wednesday with some showers continuing along with below normal temperatures. Flat ridging should then bring a drier and warmer end to the workweek.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1043 AM MDT Sat May 16 2026

VFR conditions prevail over the next 24 hours; however, MVFR to IFR conditions will begin Sunday afternoon and evening as precipitation begins with the incoming weather system.

Today will feature breezy winds at many terminals, with isolated showers moving through the region. Most clouds will be high cirrus, but some mid-level moisture is possible across southern to central Wyoming. CPR and RKS have the best chance (about 30%) of seeing a brief passing rain shower from these mid-level cloud decks this afternoon.

Clouds thicken and lower tonight into Sunday morning, as winds shift from westerly to northeasterly at many sites. The deeper moisture and better chances for rainfall and rain mixing with snow will be during the late afternoon and evening, as temperatures cool. Expect mountain obscurations to become widespread Sunday afternoon. Impactful winter weather will affect many locations beginning Sunday night.

FIRE WEATHER

Issued at 259 AM MDT Sat May 16 2026

Today will be one more day of warm temperatures, gusty wind and relative humidity falling into the teens. As a result, expect another afternoon of elevated to near critical fire weather. An approaching low pressure areas will bring much cooler temperatures as well as rain and snow chances Sunday into Monday.

RIW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 6 PM Sunday to 6 PM MDT Monday for WYZ002-003-005-007>011-014-016>018-026-028-029.

Winter Storm Warning from 6 PM Sunday to 6 PM MDT Monday for WYZ015-019-020-022-030.