High pressure will be centered near the Four Corners region during the middle part of the week with abundant monsoonal moisture rotating around the high in a clockwise (anti-cyclonic) direction.

This pattern will favor significant rainfall across the Southwest over the next several days, including a high risk for flash flooding in slot canyons, dry washes, and wildfire burn scars. 

Daily thunderstorms with significant lightning risk can also be expected across the higher peaks of Colorado and Utah, so if you have peak-bagging plans, you'll want to aim for alpine starts and keep a close eye on the skies for early thunderstorm development. "Be off the summit by noon" does not always apply during active monsoon patterns, as sometimes storms develop earlier.

Heavy rain, runoff on steep slopes, and wet rock and trail conditions should be expected during thunderstorms in the Colorado, Utah, Arizona, and New Mexico mountains as well.

Check out the 5-day precipitation projection from the European Model, from Wednesday morning through Monday morning.

Taking a look at the upper atmospheric weather map for Wednesday, we can see high pressure located near the Four Corners and monsoonal moisture rotating around the high.

Farther north, monsoonal moisture will also impact the Northern Rockies with elevated thunderstorm activity expected for this region – though rain amounts will be less compared to farther south.

The Pacific Northwest is also experiencing a cooldown, especially west of the Cascades where a trough of low pressure is located allowing for a strong marine push.

Atmospheric moisture levels will be above average for most of the Rocky Mountain and Great Basin regions on Wednesday, hence the elevated thunderstorm and heavy rain potential.

Temperatures over the next 5 days will be below average across the Southwest, in response to greater moisture and cloud cover. The Pacific Northwest west of the Cascade crest will also enjoy cooler than average temperatures. The warmest temperatures relative to average will be over the Northern Rockies east of the Continental Divide.

Fires continue to burn across the Northwest, while areas being impacted the most by the monsoon continue to see a reduction in fire danger compared to earlier in the summer.

One-thousand-hour fuel moisture is a good measure of the potential for wildland fires (as opposed to grass/brush fires) to burn effectively with 10% being a critical threshold. Much of the West is currently below 10% fuel moisture at this point, though monsoon relief across the Four Corners has suppressed fire danger.

On the other hand, fire danger remains very high across California, the Inland Northwest, and the Northern Rockies. Fire danger is lower west of the Cascade crest in Washington and Oregon.

Forecast for Wednesday, July 21st

Western Colorado and Northern Arizona/New Mexico will see the most widespread thunderstorm activity on Wednesday afternoon, though Southern Utah and Eastern Utah will get in on the action as well with "heavy rainers" possible.

Farther north, a disturbance moving across Idaho and Montana will interact with monsoonal moisture to result in an uptick in thunderstorms with wetting rains possible. 

Forecast for Thursday, July 22nd

Showers and thunderstorms will really begin to ramp up across Arizona, New Mexico, and Southwest Colorado with heavy rain and localized flash flooding possible. Thunderstorm activity will be more isolated the farther north you go, but mountain ranges such as the Uintas, Wind Rivers, Tetons, Beartooths, and Bighorns could see some respectable storms with wetting rains.

Forecast for Friday, July 23rd

The flash flooding risk will further increase on Friday with widespread soaking rains possible across a large chunk of Arizona. Heavy rain and flash flooding will be possible across New Mexico, Utah, and Colorado as well. Thunderstorms will be more isolated across the Northern Rockies as a drier westerly flow begins to take hold.

Forecast for Saturday, July 24th

Little change to the weather pattern is expected for Saturday with widespread thunderstorms and heavy rain/flash flooding across the Four Corners states – especially in Arizona. Drier conditions and fewer thunderstorms are expected north of the Medicine Bow's/Snowy's in Southern Wyoming.

Forecast for Sunday, July 25th

Another busy day is expected across the Four Corners region on Sunday with heavy rain and flash flooding potential. Arizona will remain under the bullseye while Southern Utah could also see an increase in thunderstorms and heavy rain compared to prior days.

Outlook for Mon, July 26 - Fri, July 30

Next week, high pressure will begin to shift eastward into the Great Plains and medium-range models are projecting a northerly surge in monsoonal moisture with the Central Rockies of Utah, Colorado, Wyoming, and Southwest Montana becoming the most favored for thunderstorms and locally heavy rains.

The Sierras could also see enough moisture extend westward for a day or two of elevated thunderstorm potential.

Most of Arizona and New Mexico should see a decrease in thunderstorms and heavy rainfall compared to the prior week, with more isolated storm coverage expected.

Thanks so much for reading! Next update on Friday (7/23).

ALAN SMITH

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