The ridge of high pressure responsible for recent hot weather across the Western U.S. has started to weaken, while monsoonal moisture has continued to increase across the Four Corners region.

In addition, an organized disturbance is dropping into Colorado and Northern New Mexico from the northwest, which will interact with monsoonal moisture to result in an uptick in thunderstorms on Wednesday.

By Friday, high pressure will continue to weaken with the monsoonal circulation centered around the Four Corners. Farther north, a trough of low pressure will usher in cooler temperatures and even some showers across Western Washington.

Over the weekend, high pressure will rebuild across the Rockies with significant warmth expected by late in the weekend across the Central and Northern Rockies. The monsoonal flow will shift farther west a bit, favoring Arizona and Utah and extending into the Sierras.

Forecast for Wednesday, July 14th

Hotter than average temperatures are expected across the Inland Northwest, while near to below average temperatures will prevail east of the Continental Divide and around the Four Corners. 

Widespread thunderstorms and wetting rains will occur on Wednesday across the Four Corners states and into Eastern Nevada, with more isolated activity north of the Wyoming border.

The Four Corners will see an elevated risk for flash flooding in slot canyons and dry washes, especially in Arizona and Western New Mexico.

Forecast for Thursday, July 15th

A marine push will usher in cooler temperatures across the West Coast, especially in Washington and Oregon. Above-average warmth will prevail across the Northern Rockies.

Arizona and New Mexico will be the most favored for thunderstorms and heavy rain, while storm activity will be less widespread across Utah and Colorado compared to Wednesday. Farther north, another disturbance will bring isolated "dry" thunderstorms to portions of the Northern Rockies. The Sierras could see a few thunderstorms as well.

The risk for flash flooding will persist across Arizona and New Mexico, as well as Southern Colorado.

Forecast for Friday, July 16th

The Northwest Coast, and to a lesser extent the California Coast, will continue to trend cooler as a trough of low pressure advances into the region. Warmer than average temperatures will prevail across the Great Basin and Rockies.

Scattered afternoon thunderstorms with locally heavy rains can be expected once again across the Four Corners states with more isolated activity farther north. Light showers will also develop across the Washington Coast and western slopes of the Cascades.

Forecast for Saturday, July 17th

Little change in the temperature pattern is expected Saturday with cooler temperatures along the West Coast and warmer temperatures inland.

The Four Corners states will continue to be favored for thunderstorms on Saturday with locally heavy rains possible, especially in Arizona and New Mexico.

Forecast for Sunday, July 18th

Temperatures will really start to heat up across the Central and Northern Rockies on Sunday in response to a strengthening ridge of high pressure centered near the UT/WY/CO border region.

The monsoonal flow rotating clockwise (anticyclonically) around the center of high pressure will stretch westward on Sunday. Southwest Colorado, New Mexico, and Arizona will be favored for the most widespread thunderstorm activity, while the Southern California Mountains and Sierras should start to get in on the action as well.

Outlook for Mon, July 19 - Fri, July 23

High pressure will remain centered in the vicinity of the UT/WY/CO border region next week, initially leading to hot temperatures for the Central and Northern Rockies. However, monsoonal moisture will increase across the Great Basin and eventually surge northward into the Northern Rockies.

New Mexico, Arizona, and Southwest Colorado will continue to be favored for thunderstorms. However, thunderstorm activity and wetting rains will also extend into Utah, Nevada, and the Sierras, and by later in the week farther north into the Greater Yellowstone Region of Idaho/Wyoming/Montana.

The hottest temperatures relative to average next week can be expected across the Northern Rockies, especially early in the week before significant monsoon relief arrives.

Thanks so much for reading! Next update on Friday (7/16).

ALAN SMITH