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Recent Conditions:

Tropical Storm Alvin developed in the Eastern Pacific last weekend, and a stalled area of low pressure over Southern California pulled moisture from this system into the Southwest. 

The Southwest, which is typically very dry in early June, has seen quite a bit of rain in recent days as a result. Areas east of the Divide in Colorado, Wyoming, and Montana have also received heavy rainfall over the past few days.

The map below shows estimated rainfall from June 1-3. As of this writing, new rainfall totals over the past 24 hours ending on the morning of June 4 had not been added to this map yet.

Wednesday (June 4) to Thursday (June 5):

Moisture from the remnants of Tropical Storm Alvin will remain over the Southwest over the next couple of days, leading to continued active weather.

Two low pressure troughs will move across the West on Wednesday and Thursday, and will interact with this moisture to result in showers and thunderstorms over the Southwest, High Sierra, and Eastern Rockies. 

Moisture will be most abundant across the Southwest in the vicinity of a low-pressure area moving across Northern Arizona.

The Four Corners region, as well as portions of Nevada and California, will see numerous showers and thunderstorms with stronger thunderstorms capable of producing heavy rain, frequent lightning, marble-size (or larger) hail, and localized flash flooding. 

The Northern Rockies east of the Divide (Wyoming and Southern Montana) will also see active conditions on Wednesday and Thursday with scattered showers and thunderstorms as a trough passes over the region. A few stronger storms with frequent lightning, small hail, and heavy rain can be expected in this region.

NOAA's Weather Prediction Center has issued a Slight (level 2 out of 4) risk of flash flooding across the Four Corners region extending as far west as Vegas. Many popular national parks and slot canyon hiking regions are included in this risk, such as Zion, Moab, and the Grand Canyon. 

Of the two days, Wednesday will be the most active with stronger thunderstorms across the West and a higher risk of flash flooding. However, Thursday will also be active, and there will be at least some risk of strong thunderstorms and flash flooding. 

Here is a 2-day rainfall projection from the European Weather Model. The Four Corners region, Colorado Front Range, and the Wind River and Bighorn Ranges in Wyoming are in line for the highest rainfall totals, while the High Sierra in California will pick up some good rainfall as well. 

Temperatures will also be cooler than average across the Southwest and the Rockies on Wednesday and Thursday, with conditions feeling more spring-like than summer-like, even though we are officially now in meteorological summer (which is defined as the 3-month period from June 1 to August 31).

Warmer temperatures will prevail across the Far West, however, as a high-pressure ridge pushes into this region from the west. 

Given the cooler airmass, the higher peaks will pick up some snow in this pattern. Snow levels will be lower in Wyoming, dipping down to 8,000 feet at times, and heavier snowfall can be expected in the Wind River and Bighorn Ranges as a result.

Snow levels will be a bit higher over Colorado, the Southwest, and the High Sierra, ranging from 11,000 to 12,500 feet. But the higher peaks in these regions will still get dusted with snow.

Friday (June 6) to Sunday (June 8):

Heading into the weekend, troughing over the Rockies and Southwest will begin to exit eastward out into the Central U.S., and a strong ridge over the West Coast will begin to push inland.

This will lead to an overall warming and drying trend across the West. However, enough moisture will linger to support daily rounds of terrain-driven afternoon thunderstorms each day from the High Sierra to the Utah and Colorado Rockies.

By Saturday and Sunday, most of the West will be warmer than normal, with more summer-like temperatures taking hold. Temperatures are expected to be well above normal underneath the high-pressure dome in the Pacific Northwest, with interior areas away from the coast likely to see their first heatwave of the season. 

Outlook for June 9-16:

The heat will persist over the Pacific Northwest and California into early next week, but then a trough-dominant pattern will gradually take hold over the Northwest as ridging weakens and pushes eastward over time. 

Starting Tuesday, the Northwest is expected to see a noticeable cooling trend with temperatures potentially dipping below normal, while California and the Rockies are expected to remain above normal. 

The rainfall outlook is fairly seasonal for June with better rain chances over the far Northwest and Canada, the Northern Rockies, and along/east of the Continental Divide in Colorado and New Mexico.

Drier conditions are expected over the Southwest, Great Basin, and California, as is typical at this time of year.

Here is a 7-day rainfall projection from the European Ensemble Model, which represents the average of 50 simulations of this model. 

Thanks so much for reading! Next update on Friday (June 6).

Alan Smith