Big Picture:

A strong ridge of high pressure has set up over the Pacific Northwest and Western Canada, resulting in a multi-day heat wave across the region. The worst of the heat is expected away from the coast and across the Inland Northwest, but even the west side of the Cascades will be toasty. 

To the south, the monsoon has become more consistent across the Southwest with moisture favoring the Four Corners states as well as the Sierra Nevada Range in California.

An area of low pressure is located just off the California coast while an area of high pressure is located over SE New Mexico. Slight day-to-day fluctuations in these features will result in minor changes in moisture and wind, and as a result, which mountain ranges will see more thunderstorms on a given day. 

Over the next five days, temperatures will be well above average across the Northwest. Temperatures will be near to below average across the Four Corners region as well as the Sierra Nevada Range thanks to higher moisture levels. 

Fire and Smoke Outlook:

Fire activity has increased across Oregon in recent days as a hot and dry pattern has taken hold. An uptick in smoke has occurred across Central Oregon as a result.

Fires are also ramping back up across BC and Alberta and smoke has increased across these areas as well. Portions of the Inland Northwest and Northern U.S. Rockies may also see smoke at times this week. 

Fire danger looks to remain high across the Northwest through the first half of this week due to hot and dry conditions, along with occasional gusty winds and the potential for dry thunderstorms.

Forecast for Monday Afternoon to Monday Night:

Thunderstorm activity will be most widespread across Eastern Arizona, Western/Northern New Mexico, and Southwest Colorado with more scattered activity across Southern Utah. Thunderstorm chances will also be high across the Central Sierra Nevada Range including Tahoe.

Stronger storms will be capable of producing frequent cloud-to-ground lightning and heavy rain, with isolated flash flooding possible in slot canyons and dry washes. This will be true across the Southwest and Sierra throughout the week. 

Forecast for Tuesday:

Thunderstorm activity in the Southwest will shift westward and northward just a bit with an uptick in activity expected across Northern Arizona as well as Utah (from the parks all the way northward to the Wasatch and Uinta).

New Mexico will see another active day of thunderstorms, while most of the action in Colorado will be confined to the San Juans and southern/western portions of the state with little activity expected in Northern Colorado.

Across the Far West, scattered thunderstorms can be expected throughout the Sierra Nevada Range. Enough moisture may also sneak into the Oregon Cascades for some isolated thunderstorms, but these will be more of the "dry" variety which will result in an increased threat of lightning-triggered wildfires.

Forecast for Wednesday:

Scattered thunderstorms can be expected throughout the Four Corners region with an uptick in storms also expected across Central and Northern Colorado including the Front Range, while the San Juans will likely see the most widespread storms and heaviest rainfall.

Another active day can also be expected across the Sierra, while Southern Oregon could see isolated dry thunderstorms and another day of elevated fire weather concerns. 

Forecast for Thursday to Friday:

A trough of low pressure will set up near the West Coast late this week, with south/southwest winds keeping a consistent flow of monsoonal moisture going across the Southwest, Great Basin, and Sierra. In addition, moisture will expand northward a bit, especially by Friday, with increasing thunderstorm chances across Oregon, Idaho, and Wyoming. 

The Northwest will finally see the heat wave break on Friday as cooler air arrives from the Pacific. A low pressure system will also drop into the Canadian Rockies from the northwest on Friday, resulting in more widespread showers and thunderstorms for portions of Eastern BC and Western Alberta. 

Forecast for Saturday (Aug 19) to Thursday (Aug 24):

This period is looking wet and stormy across the West as a deep trough of low pressure will be located near the West Coast, with consistent south/southwest winds ushering in an abundance of monsoonal moisture.

Western portions of the Southwest (Utah/Arizona/Nevada) look most favored while significant moisture may also reach the Northern Rockies and Inland Northwest.

Temperatures are also expected to be below average across the Great Basin and western portions of the Southwest, thanks to the uptick in moisture. Areas near the West Coast and most of the Central Rockies are expected to see near to above-average temperatures. 

Thanks so much for reading! Next update on Wednesday (August 16).

Alan Smith