Forecast Highlights:

• Monsoon thunderstorms favor New Mexico, Arizona, Southwest Utah, California, Nevada, Oregon, and Western Idaho from Monday through Wednesday.
• Elevated flash flood threat for slot canyons/dry washes in Arizona and Southern Utah on Tuesday & Wednesday. Mountainous terrain across much of the West could see isolated flash flooding as well.
• Pacific Northwest thunderstorms expected across Oregon on Monday, then Oregon and Washington on Tuesday-Wednesday including the Olympics, Cascades, and Inland Northwest.
• Hotter than average temperatures across the Northwest on Monday and Tuesday will moderate somewhat (mainly west of the Cascades) later in the week.  
• Late week monsoon surge expected across the Central and Northern Rockies, while Arizona/Southern Utah also remain in a wet/stormy pattern. 

Synopsis:

An area of low pressure has set up in the Pacific Ocean off of the Northern California Coast, while high pressure is centered near the Utah/Colorado border. An active monsoon pattern remains in place across the Western U.S. and on Monday, with monsoon moisture favoring New Mexico and Arizona as well as the Sierra and Great Basin. Moisture will also extend northward into the Pacific Northwest over the next couple of days, while the Central Rockies will see a temporary drying trend.

Monsoon Update:

Following a wet weekend across the Colorado Front, Range, moisture is shifting southward into New Mexico and Arizona, just to the south of an area of high pressure centered near the Utah/Colorado border.

Meanwhile, southerly flow out ahead of a low pressure system located off of the West Coast will transport anomolously high levels of monsoonal moisture into California and Nevada where heavy rain will be possilbe over the next couple of days. 

Monsoonal moisture will also work its way northward into Oregon, Washington, and Western Idaho by Tuesday with increasing shower/thunderstorm activity. However, it will be a mix of wet and dry thunderstorms across the Northwest as fast storm motions will limit the potential for widespread wetting rains. 

On Wednesday, showers and thunderstorms can be expected across the Olympic and Cascade Mountains as the low pressure system moves northward, to just west of the Oregon and Washington coastlines.

Monsoonal moisture will also increase across the Inland Northwest, Idaho, and Great Basin with a later day uptick also occurring across Northern Utah. A consistent monsoon thunderstorm pattern will continue across Arizona and Southern Utah, where desert/canyon country flash flooding will be a concern each day from Monday through Wednesday (and beyond).

The heaviest 3-day rain totals from Monday to Wednesday will favor New Mexico, Arizona, Southwest Utah, Nevada, the Sierra Nevada Range in California, Eastern Oregon, and Western/Central Idaho.

Lightning Outlook:

On Monday, thunderstorm/lightning activity will be most active across Northern New Mexico, Arizona, and Southern California. Colorado will see reduced thunderstorm activity compared to recent days, with isolated activity primarily confined to southern portions of the state as well as the Front Range. 

Isolated to scattered thunderstorms can also be expected across the Sierra Nevada Range and Great Basin with a few dry thunderstorms possible across Oregon as well. In fact, fire danger will be elevated in Oregon due to dry fuels and the potential for dry thunderstorms.

On Tuesday, lightning activity will be most active across Arizona, Southern Utah, Nevada, the Sierra Nevada Range, and Eastern Oregon, while the San Juans in Colorado and Central/Western New Mexico will be fairly active as well. 

Isolated thunderstorms will also develop across the Oregon/Washington Cascades on Tuesday afternoon, and (not shown here) there is also a higher threat of overnight/early Wednesday storms across the Cascades and Olympics, coastal areas of Washington, and Inland Northwest.

On Wednesday, the focus of thunderstorm activity will shift eastward a bit, favoring Arizona, Utah, Nevada, and Idaho. Thunderstorm activity will also increase across Western Colorado while New Mexico will remain in a daily scattered thunderstorm cycle. Isolated storms could also reach Southwest Montan and Western Wyoming, with lightning remaining possible across the Pacific Northwest as well.

Temperature Outlook:

The general theme this week will be above-average temperatures across the Northwest and Northern/Central Rockies and below-average temperatures across the Southwest.

The Pacific Northwest is experiencing a less-severe heatwave (compared to 1-2 weeks ago) on Monday and Tuesday, then will see cooler air arrive on Wednesday, mainly west of the Cascades. Temperatures will then trend warmer again on Thursday and Friday.

Further south, abundant monsoon moisture will have a moderating effect on temperatures this week.

Fire and Smoke Outlook:

Thanks in part to a very active monsoon, the smoke situation really isn't bad across most of the West, aside from localized areas near and just downwind of the handful of major fires that are currently ongoing. 

Right now, the most active fires that are producing locally smoky conditions are the McKinney Fire (Northern CA), Cedar Creek Fire (OR), Moose Fire (ID), Elmo Fire (MT), and Keremeos Creek Fire (BC).

Monsoon moisture surging into the Pacific Northwest and Interior Northwest could be a good or bad thing this week.

Thunderstorms across Oregon, Washington, and Northern Idaho are expected to be a mix of wet and dry thunderstorms, meaning localized areas could see wetting rains, while the potential for lightning-triggered fires is also a concern. This is especially true across the Inland Northwest where fuels are drier and more primed to burn.

Elsewhere across the West, recent and upcoming rainfall associated with an active monsoon should limit the potential for significant fires.

Outlook for Thursday (8/11) to Sunday (8/14):

On Thursday, low pressure will be centered just off the Washington Coast and will remain nearly stationary in the days to follow. The jet stream will also push inland a bit, and this will shift the flow of monsoonal moisture inland, with the flow extending from Arizona into the Central and Northern Rockies.

As a result, more widespread thunderstorms can be expected on Thursday and Friday across Northern Utah, Eastern Idaho, Western Wyoming, and Southwest Montana. Moisture levels will be high in this pattern, resulting in the potential for heavy rainfall across these areas.

Arizona, Southwest Utah, and Eastern Nevada will see numerous thunderstorms with heavy rainfall as well, while Western and Central Colorado will see more "scattered" activity. The Central and Southern Sierra could see some isolated thunderstorms as well, but with less coverage than prior days.

Heading into the weekend, a very similar pattern is expected on Saturday (compared to Thursday and Friday) with scattered to widespread thunderstorms capable of heavy rain across the Central and Northern Rockies, as well as the Arizona/Southern Utah Canyon Country.

On Sunday, the focus of monsoon showers and thunderstorms may start to shift eastward a bit compared to prior days. 

Outlook for Monday (8/15) to Monday (8/22):

The Pacific Northwest could be in for another stretch of hot weather during the third week of August with well-above-average temperatures expected. Above-average heat is projected across California as well.

The Southwest and the Central Rockies will be favored for near to below-average temperatures as an active monsoon pattern continues.

The third week of August is also looking wet and stormy across a large portion of the West, as an active monsoon continues. Above average rainfall is expected throughout the Southwest, Great Basin, Central and Southern Rockies, and portions of Southern California and the Sierra Nevada Range.

Thanks so much for reading! Next update on Wednesday (8/10).

ALAN SMITH