Big Picture:

The remnants of tropical storm Harold will move into Colorado on Friday with an abundance of moisture along with weak winds aloft resulting in the potential for widespread and slow-moving showers and thunderstorms. A cold front sneaking into Northeast Colorado will also result in low-level upslope winds blowing from the east, which will favor the Colorado Front Range east of the Divide.

A Flash Flood Watch is currently in effect for much of Northeast Colorado and Southeast Wyoming. Burn scars, steep/rocky terrain, and small streams will be the most susceptible to flooding, as will urban areas with poor drainage.

Utah will also be a favored area for thunderstorms on the western side of this moisture circulation. A powerful trough of low pressure centered well off the West Coast will result in southerly winds across the Pacific Northwest that will transport moisture into the region, resulting in scattered showers and thunderstorms across the Cascades and Inland Northwest on Friday and Saturday.

Following a reprieve over the past few days, temperatures will heat back up substantially across the Pacific Northwest and especially Western Canada this weekend. By Tuesday, temperatures will start to cool off as a low pressure system makes landfall.

Temperatures from California to the Central Rockies will be on the cooler side of average on Friday and into the weekend before warming up early next week.

Fire and Smoke Outlook:

Fire activity and intensity have quieted down across the Northwest in recent days thanks to cooler and wetter conditions. Smoke has still lingered across much of the Northwest up through Thursday, but models are projecting a decrease in smoke intensity on Friday with most of the Northwest and Northern Rockies experiencing lighter smoke.

The main exception will be areas near the Smith Complex Fire in Northwest California and northern portions of BC and Alberta where heavier smoke is expected. Also, offshore winds (blowing from east to west) could result in moderate smoke across portions of the Northwest coastal regions this weekend. 

More smoke maps:

• Smoke (Surface) Map → Regular | U.S. Lower 48 States & Canada
• Smoke (Surface) Map → High Resolution | U.S. Lower 48 States

Hotter and drier conditions may allow for some ongoing fires to flare back up again in BC and the Northwest. However, cooler and wetter conditions are expected early next week which should help to temper fire behavior.

Forecast for Friday:

Widespread showers and thunderstorms can be expected throughout Colorado with locally heavy rain possible in all areas. More widespread heavy rain along with higher flash flood potential will exist across the Front Range and adjacent plains.

Scattered showers and thunderstorms can also be expected across portions of New Mexico, Utah, and Wyoming, with more isolated activity in Arizona. Also, southerly winds across the Far West will transport moisture into the Great Basin and Northwest, resulting in scattered showers and thunderstorms.

Forecast for Saturday:

Lingering moisture will result in another wet day across Colorado with widespread showers and thunderstorms expected, favoring the Front Range and Sangre de Christo Range. Thunderstorms will also be more numerous across New Mexico. Locally heavy rain will remain possible.

Isolated to scattered storms can also be expected across Arizona, Utah, Oregon, Idaho, Wyoming, and Montana. Locally heavy rain is possible in any of these areas, with isolated flash flooding possible in dry washes and slot canyons.

Forecast for Sunday:

Moisture will remain over Colorado and New Mexico, resulting in another active day. Rainfall amounts do not look as heavy compared to Friday and Saturday, but thunderstorms may be more common with frequent lightning activity and locally heavy rain is still possible. The Sangre de Christo Range in Southern Colorado and Northern New Mexico looks most favored.

A disturbance will also move across the Northern/Central Rockies, with an uptick in thunderstorms expected across Wyoming, Southwest Montana, and Central/Eastern Idaho.

Forecast for Monday to Tuesday:

Moisture will remain in place over the Southern Rockies with thunderstorm activity favoring New Mexico, Colorado, Southeastern Arizona, and to a lesser, extent Central Wyoming. Utah looks drier with only isolated storms expected. 

A trough of low pressure will also move into the Northwest during this period, resulting in more widespread showers across portions of BC, Washington, Northern Oregon, Idaho, and Montana. Significant rainfall is possible across this region, which would be great news from a fire standpoint.

Outlook for Wednesday (Aug 30) to Sunday (Sep 3):

The Northwest should see some lingering moisture from the early week system on Wednesday, then another system could potentially bring showers to the region heading into Labor Day weekend. Meanwhile, an active monsoon is expected across the Southwest, Rockies, and possibly the Sierra during this period with moisture favoring areas west of the Divide.

Above-average temperatures are favored across the Southwest and the Rockies during this period, especially east of the Continental Divide. Temperatures are expected to be near average across the Northwest.

Thanks so much for reading! Next update on Monday (August 28).

Alan Smith