The monsoon pattern is in peak form right now and will impact a large portion of the Western U.S. with elevated thunderstorm chances this week.

As we start the week, high pressure is centered over Western Colorado/Wyoming, and monsoonal moisture is rotating around the high in a clockwise (anti-cyclonic) direction, streaming into Utah, Nevada, California, and northward into Idaho and Wyoming.

Atmospheric moisture anomalies are substantial across the Great Basin region, which will provide plenty of fuel for thunderstorms and locally heavy rains over the next couple of days. Flash flooding will also be a concern for slot canyons, dry washes, and wildfire burn scars.

As of early Monday afternoon, showers and thunderstorms had already developed across much of the Interior West from Arizona to Montana.

Lightning activity was numerous during the early afternoon period across the Sierras and Great Basin as well.

Current Radar

Lightning Density

Forecast Radar

Taking a look at our estimated trail conditions feature, we can see that Kuna Peak (a 13,000 foot peak in the Sierras) is picking up on wet trail conditions based on recent rainfall that moved through the area per radar.

As the week progresses, monsoonal moisture will expand eastward, favoring the Four Corners states for thunderstorm activity west of the Continental Divide, and extending north into the Wind Rivers, Tetons, and Greater Yellowstone Region.

Northern Utah will see an uptick in storm activity compared to recent weeks as well, especially the Uinta Range. Check out the 5-day forecast for Kings Peak, which is the highest point in Utah.

The rainfall is generally welcome across the West right now, though there are some secondary concerns of lightning-triggered fires for areas that happen to miss out on significant rainfall but experience cloud-to-ground lightning.

However, large fires ongoing across the Northwest will see little in the way of moisture, as is typically the case at this time of year.

Numerous fires continue to burn from California to British Columbia and eastward into Idaho and Montana. As a result, the Interior Northwest and portions of the Northern Rockies will continue to be impacted by varying degrees of smoke for the foreseeable future.

In addition, light to moderate smoke from fires in Saskatchewan and Manitoba is also impacting areas east of the Continental Divide from Montana to New Mexico.

Forecast Smoke (surface)

Forecast Smoke (sky)

Forecast for Monday, July 19th (PM):

Portions of the southwest and Great Basin are experiencing cooler than average temperatures on Monday afternoon due to the presence of monsoonal moisture and greater cloud cover, while hotter than average temperatures remain over the Northern Rockies and Inland Northwest.

The most widespread thunderstorm coverage and wetting rains on Monday afternoon and evening can be expected across Arizona, Utah, Nevada, and the Sierras in California, with more isolated thunderstorms farther east toward the Continental Divide. Some areas from Utah into the Northern Rockies will see overnight activity as well.

Forecast for Tuesday, July 20th

Temperatures will not deviate too far from average on Tuesday, except for some lingering warmth across the far Northern Rockies. A marine push will also lead to cooler temperatures across Coastal Washington and Oregon.

Widespread thunderstorms and wetting rains can be expected across much of the Rocky Mountain region from Utah and Western Colorado northward into Idaho and Montana. Storm activity will be more isolated over Arizona but locally heavy rains will still be possible across all of the Rocky Mountain states.

Forecast for Wednesday, July 21st

Most of the West will undergo a slight warming trend, except for Coastal Washington and Oregon where below-average temperatures will prevail.

The Four Corners region will see the most widespread thunderstorm activity with locally heavy rains and a threat for flash flooding expected once again. Most of the storms will develop along and west of the Continental Divide. Elevated moisture levels will result in isolated to scattered thunderstorms across the Northern Rockies as well.

Forecast for Thursday, July 22nd

Cooler air will continue to overtake the Pacific Northwest on Thursday, even extending into the Inland Northwest with below-average temperatures as far east as Northern Idaho. Farther east, a more substantial warm-up is expected across the Central and Northern Rockies near and east of the Divide.

Moisture and thunderstorm activity will increase across the Four Corners region including a more substantial threat for flash flooding, especially across Arizona. The Northern Rockies and Eastern Great Basin will continue to see thunderstorms as well, though coverage will be less widespread compared to areas farther south.

Forecast for Friday, July 23rd

Temperatures will be warmer than average across most of the West on Friday, except for Arizona and New Mexico where greater cloud cover will result in below-average temperatures.

Thunderstorms and heavy rain are expected across the Southwest once again with an elevated flash flood threat for slot canyons and dry washes. The Central Rockies of Utah and Colorado will see high thunderstorm and lightning potential as well, so be cautious if you have peak-bagging plans.

Outlook for Sat, July 24 - Wed, July 28

Over the weekend, an active monsoonal flow will persist across the Four Corners states with a gradual drying trend expected across the Northern Rockies.

Heading into early next week, moisture will begin to surge northward and, to some extent, westward with areas such as the Sierras, Wind Rivers, and Tetons seeing an increase in thunderstorm activity along with continued daily storms for the Central and Southern Rockies.

High pressure will generally remain in a favorable position for a consistent flow of monsoonal moisture, with an average location near the Four Corners.

From Saturday through Wednesday, above-average precipitation is projected for the Southern/Central Rockies, Southwest, and Great Basin, with below-average precipitation farther north toward the Canadian border and also across the Cascades.

Thanks so much for reading! Next update on Wednesday (7/21).

ALAN SMITH

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