textproduct: Western and Central Wyoming

KEY MESSAGES

- Mainly dry and warmer to start the holiday weekend with any afternoon showers largely confined to in and near the mountains.

- Increased chances of showers and thunderstorms Sunday and Monday, mainly across western and southern Wyoming.

- A cooler and wetter pattern may move in for next week, but uncertainty on details remains high.

DISCUSSION

Issued at 247 AM MDT Sat May 23 2026

We have now entered the unofficial start of summer (for tourist reasons anyway, meteorological summer starts June 1 and astronomical summer on June 21). And in western and central Wyoming, Memorial Day weekend is traditionally by far the wettest of the three main holiday three day weekends. A graphic we posted a few years ago shows greater than half of our main climate sites have had at least half of Memorial Days since 2003 had had at least some rain. In my 14 years at this office, I have seen everything from 90 degree heat to severe thunderstorms to even snow at the office. This weekend will be on the drier end, but not completely dry. And rain chances will increase as the weekend progresses.

A subtle shortwave is moving across northern portions of Wyoming, and we do have some returns on radar. Many of these are probably not reaching the ground though. A few of the latest hi resolution model runs do show a few showers this afternoon. However, precipitable water values are below normal (generally 60 to 80 percent of normal). This being a holiday weekend, we did add a 1 in 5 chance of showers but only over the mountains and even here most showers would be high based with model soundings showing inverted V signatures, so most would end up as virga showers. These could produce strong wind gusts though. However, a vast majority of the area should stay dry with just some afternoon cumulus buildup. I also can't rule out a but of thunder, but it would be very isolated so we left it out of the forecast for now. Temperatures should run close to seasonal averages with a bit of an afternoon breeze, but nothing unusual for Wyoming. Any showers should end fairly quickly after sunset with dry conditions Saturday night.

Flow turning southwest will warm temperatures to above normal levels for Sunday. Chances of showers will begin to rise on this day though with another shortwave moving through. Precipitable water values begin to rise this day, but not an extreme amount. They do rise to above normal levels across southern Wyoming as southwest flow brings in some increased moisture, but remain near to below normal in northern Wyoming. With this, any convection was kept largely across the southern half of the state. Coverage still looks fairly sparse, generally a 1 in 3 chance or less in any particular location. Again, this will be largely diurnal with almost all showers ending shortly after midnight. Monday at this point looks fairly similar, with most showers being confined to southern and western Wyoming with dry air holding in the lower levels areas further north and east for another day.

Things get more uncertain as we head into next week. And the reason why will be what happens with a big atmospheric bowling ball, A.K.A. an upper level low, that will be moving onshore in the Pacific Northwest on Monday and progressing onshore. It will be a slow mover as well, as it is rather vertically stacked and may end up cutting off. The big X factor is what will happen further to the east. A very strong ridge will be building across the northern United States, possibly developing into a blocking ridge. The question is where will it set up as this will determine the movement of the low. Some ensemble members, as well as the deterministic GFS, show the ridge axis closer to the Great Lakes. This would allow the upper level low further east, bringing deeper moisture to the Cowboy State, with precipitable water levels rising as high as 150 percent of normal and better chance of showers and thunderstorms. Other ensemble members, as well as the deterministic European, keep the ridge axis further west, which would hold the low and deeper moisture further west, resulting in a drier and warmer pattern. At this point, which would occur is basically a coin flip. Periods of heavier showers would be determined by shortwaves rotating around the low. At this point, the forecast this far out has more moving parts than a Rube Goldberg machine so details are difficult. At this point, the end of next week, like Thursday and Friday would be more favored but placement of heaviest precipitation is impossible this far out. There is a reason old time forecasters called upper level lows "Upper Level Devils". Stay tuned.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 407 AM MDT Sat May 23 2026

VFR conditions prevail through the TAF period. Isolated virga/showers will develop Saturday afternoon, mainly in and near the mountains. Chances are much too low (less than 20 percent) to include even PROB30 groups for rain. Did keep the VCSH at KCOD as some showers may develop in the Absarokas in the vicinity of KCOD. Wind will increase Saturday morning into Saturday afternoon. Most terminals will have wind increase to 10-20 knots, with gusts of 15-25 knots through Saturday afternoon. Wind should drop off substantially by 02Z Sunday with light wind expected Saturday night.

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.