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Recent Weather:

We are just now coming out of a cool and wet pattern over the Western U.S. that has been present over the past 7-10 days, bringing significant precipitation to some areas and temporarily slowing the rate of snowmelt.

Heading into late May, the overall trend will be toward warmer temperatures, though the Front Ranges and Eastern Plains of Colorado and Wyoming will be an exception, where a cooler and wetter pattern will prevail.

Friday (May 23):

A shortwave trough will move across the Northern Rockies on Friday, resulting in isolated to widely scattered showers and thunderstorms. Rainfall will be hit-or-miss in nature, with generally light to moderate amounts expected.

Moisture from the Gulf of Mexico will surge northwestward into Northeast Colorado, Eastern Wyoming, and the Black Hills of South Dakota near the intersection of a dryline (boundary between moist and dry air) and a stalled frontal boundary. These areas have a greater chance of seeing strong to severe thunderstorms with large hail possible. 

Saturday (May 24) to Monday (May 26):

We have a few weather features to track over the holiday weekend: the Central Rockies vicinity from Saturday to Monday, and the Pacific Northwest from Sunday to Monday.

Central Rockies to the Great Basin:

A slow-moving trough will work its way across the Southwest U.S. over the holiday weekend. Ahead of this trough, moisture levels will ramp up along the eastern side of the Continental Divide and adjacent plains, leading to frequent showers and thunderstorms with more isolated to scattered storms west of the Divide.

East of the Divide, periods of heavy cloud cover with scattered showers will be possible even during the morning hours. However, breaks in the cloud cover with sufficient heating will allow for stronger and more widespread thunderstorms in the afternoon hours along the eastern ranges and adjacent plains of Wyoming, Colorado, and Northern New Mexico. 

Stronger storms will be capable of producing heavy rainfall, and some storms near the Front Range of Colorado could also reach severe thunderstorm criteria, with large hail being the primary threat. 

West of the Divide, moisture levels will not be as high compared to East of the Divide. But enough moisture will be present along with support from the approaching trough to generate scattered afternoon thunderstorms each day over the Rockies, Great Basin, and High Sierra.

Most storms will produce brief light to moderate rain, but heavy downpours and frequent lightning are possible under stronger storms.

Here is a 3-day rainfall forecast from the European weather model. Many areas east of the Divide could see over an inch of rain, with some areas potentially seeing more than 2 inches. 

Although temperatures will be a bit warmer compared to recent days, it is still May, so the higher peaks in the Rockies can expect snow showers in this pattern.

Snow levels will generally range from 11,000 to 12,000 feet over the Colorado Rockies, while some of the higher ranges in Northern Utah and Wyoming will see snow levels of 9,500 to 11,000 feet.

Pacific Northwest:

It will be a beautiful start to the holiday weekend with mostly sunny skies and warm temperatures across the Northwest on Saturday.

However, the pattern will turn more unsettled during the second half of the weekend as a trough reaches the West Coast. Monday will be the most inclement weather day with more widespread showers and thunderstorms expected.

West of the Cascade Crest, isolated light showers will begin on Sunday afternoon following a dry start to the morning. More numerous showers can then be expected from Sunday night through Monday afternoon/evening.

Rainfall amounts will be light overall, and the risk of lightning will be low except right along the crest of the Cascades, where a few thunderstorms are possible.

East of the Cascade Crest, a more unstable atmosphere will exist, resulting in more numerous showers and thunderstorms from Sunday afternoon through Monday night. This includes the east slopes of the Cascades, the Columbia River Basin, the Inland Northwest, and Western Montana.

Thunderstorms are possible on Sunday afternoon and Sunday night, but the highest threat of thunderstorms will exist on Monday with stronger storms capable of producing frequent lightning and locally heavy rain.

Here is a 3-day rainfall forecast from the European weather model.

Outlook for May 27 to June 3:

By Tuesday, May 27th, the Pacific Northwest will begin to dry out as a trough moves eastward, with an uptick in showers and thunderstorms possible across the Northern and Central Rockies around May 27th-28th.

Aside from this mid-week trough, the overall trend over the 7-day period from May 27 to June 3 will be for a ridge of high pressure to strengthen over the Western U.S. though a weaker trough may undercut the ridge and meander over the Southwest, potentially reinforcing the flow of low level moisture east of the Continental Divide. 

Temperatures are expected to be much warmer west of the Continental Divide, rising to well-above-average levels over the Northwest especially.

However, below-average temperatures are expected to prevail east of the Continental Divide in Colorado and New Mexico, where wetter conditions are also expected. 

The next map shows a 7-day precipitation forecast from the European Ensemble Model, which represents the average of 50 simulations of this model. The heaviest rainfall is expected along and east of the Divide in New Mexico, Colorado, and Wyoming, with lighter rainfall west of the Divide.

There is also a comparatively wetter signal over the Olympics and Cascades in Washington, with even higher rainfall totals expected to the north in British Columbia. However, some dry and sunny periods are also expected in this region. 

Thanks so much for reading! Next update will be on Wednesday, May 28th.

Alan Smith

Last week, I posted a Summer Weather Forecast Preview for the Western U.S.

Check it out → 2025 Western U.S. Summer Weather Forecast Preview