The North American Monsoon is back in full force in 2021 following a couple of lackluster summers in 2019 and 2020. The drought-stricken Southwest is receiving some much-needed rainfall as a result, though flash flooding is also a significant concern for vulnerable terrain. 

Friday will be another very active day for thunderstorms and heavy rain across the deserts, canyons, and high peaks of the Southern Rockies. Check out the forecast radar for 8 pm on Friday evening, which highlights the potential for rain and thunderstorms to continue well into the night.

Current Radar

Lightning Density

Forecast Radar

Flash Flood Watches are in effect for large portions of Arizona, New Mexico, Colorado, and Southern Utah due to significant amounts of moisture in the atmosphere combined with pre-existing saturated conditions from heavy rain over prior days.

Taking a look at the big picture, monsoonal moisture is rotating around high pressure centered near Vegas, while a developing area of low pressure (not really visible yet on the below map) near the NM/TX border will help to enhance thunderstorm development on Friday afternoon and evening as well.

Farther north, a drier westerly flow will result in decreasing moisture and thunderstorm chances, stronger winds, and growing fire concerns across the Northern Rockies.

By Saturday, low pressure will set up over Arizona, leading to a shift in wind directions and storm motions, but elevated thunderstorm activity and heavy rain potential will continue across the Southwest.

As we head into early next week, California will see an interesting pattern as the mentioned area of low pressure transitions west, opening the door to a significant surge of monsoonal moisture into Southern and Central California. As a result, the SoCal Mountains and portions of the Sierras will see numerous showers and thunderstorms with the potential for heavy rain and flash flooding.

On Tuesday, the low moves well offshore monsoonal moisture will shift east into the Great Basin and Central Rockies regions, rotating via southerly flow around a ridge of high pressure setting up over the Great Plains. 

As for temperatures, above-average warmth will continue across most of the West over the next 5 days (as it has for most of the summer). The exception will be the Southwest and especially Arizona who will be running cooler than average due to significant moisture and cloud cover from Friday through Sunday.

While the Southwest will see much-needed moisture over the coming days, smoke will continue to impact much of the Interior Northwest and Northern Rockies from numerous ongoing wildfires. 

Forecast Smoke (surface)

Forecast Smoke (sky)

Forecast for Friday, July 23rd

Arizona will be under the bullseye for heavy rain and flash flooding on Friday afternoon and Friday night, but numerous thunderstorms and heavy rains can be expected throughout the Four Corners region and across the Colorado high country from the San Juans to the Front Range.

Forecast for Saturday, July 24th

The same areas will be favored for thunderstorms and heavy rain and Saturday. Overall, rain amounts shouldn't be quite as significant compared to Friday, but the risk for heavy rain and flash flooding will still remain and ground conditions will already be saturated from previous days.

Forecast for Sunday, July 25th

Another active day for thunderstorms is expected with flash flooding risks for canyons and other vulnerable areas, and significant lightning risk across the peaks of Colorado. Thunderstorm activity will also extend westward to include the Sierras and SoCal Mountains.

Forecast for Monday, July 27th

California will see its moisture surge on Monday with significant thunderstorm activity expected for the SoCal Mountains and Central/Southern Sierras, as well as the Great Basin in Nevada. California storms could produce heavy rains and localized flash flooding, and fortunately will contain enough moisture to limit the risk for lightning-triggered fires. 

Elsewhere, Arizona will see a relative break in the pattern while Utah and Colorado will be impacted by a moist southerly flow with more thunderstorms expected, especially across the San Juans, Elks, and Sangre de Christos. 

Forecast for Tuesday, July 28th

A southerly flow of monsoonal moisture will favor portions of the Great Basin and Southern/Central Rockies on Tuesday. In addition to Colorado and Southern/Central Utah who will see more thunderstorms, areas from Northern Utah to to Southwest Montana will start to get back in on the action as well.

In addition, remnant moisture could extend northward to the Southern Cascades in Oregon, resulting in a chance of thunderstorms – though perhaps of the "dry" variety, which would not be ideal for fire danger.

Outlook for Wed, July 28 - Sun, Aug 1

The monsoon will impact areas farther north next week as moisture rotates around high pressure over the Great Plains. Colorado, Utah, Nevada, Wyoming, Idaho, and Southwest Montana will all see elevated thunderstorm potential on a near-daily basis along with wetting rains. Arizona and New Mexico will continue to see storms as well, but the pattern will not be as active compared to what they are currently experiencing.

Thanks so much for reading! Next update on Monday (7/26).

ALAN SMITH

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