Forecast Highlights:

• High threat for flash flooding for parts of Utah and Colorado on Friday.
• Moderate threat for flash flooding for parts of Arizona, Nevada, and New Mexico (and also UT and CO) on Friday and Saturday.
• Widespread mountain thunderstorms with frequent lightning across the Southwest and Southern Rockies for the foreseeable future. 
• Isolated to scattered thunderstorms across the Northern Rockies and to a lesser extent the Sierra from Friday to Monday.
• Strong thunderstorm wind gusts possible across the Northern Rockies on Friday.
• Hotter than average temperatures for most of the West this weekend, excluding the Pacific Northwest.
• Smoke from the Washburn Fire in Yosemite will impact parts of the Sierra, and to a lesser extent, Nevada and Idaho.

Synopsis:

A strong ridge of high pressure over the Western U.S. will continue to result in hot temperatures, but an active monsoon will also remain in place with numerous thunderstorms along with flash flood potential for some areas. The core of monsoonal moisture will be over Arizona, Nevada, Utah, and Colorado but significant moisture is extending northward into Idaho, Wyoming, and Southwest Montana as well.

Despite the abundance of moisture, temperatures will continue to run hotter than average across most of the West this weekend and early next week. The exception will be the Pacific Northwest, mainly along and west of the Cascade crest, who will see cooler temperatures this weekend. The Northern Rockies will also see a brief cooldown early next week as a weak cold front arrives, following a hot weekend.

Fire and Smoke Update

The Washburn Fire in Yosemite National Park continues to be the most active fire across the West right now. Smoke from this fire will continue to impact portions of the Sierra most heavily, while light to moderate smoke can be expected across Nevada, Idaho, and even Western Montana from time to time.

According to the National Interagency Fire Center, parts of California, Nevada, Idaho, and Montana will see moderate to high potential for significant fires over the next week, with low potential elsewhere. 

Forecast for Friday:

Moisture levels will be significant across the Southwest and Southern Rockies on Friday and widespread thunderstorms are expected across Arizona, Utah, Colorado, and Southern Wyoming. Nevada, Northern/Western Wyoming, Eastern Idaho, and Southwest Montana will see thunderstorms as well, and some isolated activity can also be expected across the Sierra.

The threat for flash flooding and excessive rainfall will be high for slot canyons, dry washes, burn scars, and areas of steep/complex terrain in Utah and Colorado on Friday. Moderate flash flood potential will extend across Arizona, Northwest New Mexico, and Nevada as well.

Forecast for Saturday:

Monsoonal moisture will decrease a bit compared to Friday with thunderstorm coverage becoming more isolated across the Northern Rockies. Coverage will decrease somewhat across Utah and Arizona, though it still likes a fairly active day. Colorado will see the bulk of the monsoonal moisture with more widespread thunderstorms and wetting rains expected.

Across the Western ranges, some isolated thunderstorms are possible across the Sierra and SoCal Mountains, while a disturbance reaching the Northwest could generate some spotty light showers across the Cascades and Olympics.

Flash flood potential will continue across Arizona, Southern Utah, Northern New Mexico, and Central Colorado on Saturday despite the relative decrease in thunderstorm coverage. 

Forecast for Sunday:

Scattered thunderstorms with locally heavy rain and flash flood potential can be expected again on Sunday across Colorado, Utah, Arizona, New Mexico, and Eastern Nevada with isolated storms across the Sierra.

A disturbance moving across the Northwest will result in isolated light showers across the Cascades, while some monsoonal moisture will be drawn northward into Idaho, Wyoming, and Montana with isolated thunderstorms expected.

Outlook for Monday (7/18) to Tuesday (7/19):

A similar pattern is expected early next week with scattered thunderstorms expected across the Southern Rockies and Southwest with isolated thunderstorms across the Sierra. A disturbance moving across the Northwest will also trigger showers/thunderstorms near the Canadian border, while Western Wyoming should also see another round of scattered thunderstorms.

Outlook for Wednesday (7/20) to Thursday (7/21):

An active monsoon will continue across the Four Corners states with daily round of thunderstorms expected, while the Northern Rockies should see a drying trend.

Model agreement is relatively poor regarding the northern extent of the monsoonal moisture plume, with the European Model keeping moisture far enough north for action to extend into the Wasatch, Uintas, and Southern Wyoming, while the American GFS Model keeps the moisture suppressed much further south. We'll get more dialed on coverage by early next week.

Outlook for Friday (7/22) to Friday (7/29):

Hotter than average temperatures can be expected across nearly the entire West during this period, with the only exception being the Four Corners region near the core of the monsoon where temperatures will be close to average.

An active monsoon will continue across the Four Corners as well with the greatest wet signals showing up over Arizona, Southern Utah, and Western Colorado. Drier conditions are expected across the Northwest and Northern Rockies.

Thanks so much for reading and have a great weekend! Next update on Monday (7/18).

ALAN SMITH