A strong ridge of high pressure will build over the West Coast beginning on Wednesday, resulting in very hot temperatures across California, Oregon, and Washington during the days to follow. This is not on the same level as the Northwest heatwave we saw back in late June, but still quite hot for this region.

Monsoonal moisture will be confined to Arizona and New Mexico, where an area of low pressure will also support more numerous thunderstorms with wetting rains also expected. 

Later in the week, monsoonal moisture remnants will work their way north and then east into the Great Basin. By Sunday, a trough of low pressure will approach from the northwest, putting an end to the heatwave, while Arizona, New Mexico, and to a lesser extent Colorado, will see the great monsoonal influence. 

Temperatures over the next 5 days will be well-above-average across the Pacific Northwest, and below-average across portions of Arizona and New Mexico thanks to the more active monsoon.

South/southeast winds over California and along the West Coast will transport heavy smoke from large fires northward into Oregon over the next few days, and eventually into portions of Western Washington as well. The rest of the West will see varying degrees of smoke or high-level haze.

Over the weekend, winds aloft will shift to a more westerly direction as the ridge of high pressure begins to flatten. This will likely result in heavier smoke across the Rockies on Saturday and Sunday and decreasing smoke across the Pacific Northwest, especially near the coast.

Forecast for Wednesday, August 11th

Arizona and New Mexico will be the favored areas for thunderstorms, with locally heavy rain possible along with the potential for flash flooding in dry washes and slot canyons. Some of this action will extend westward into the SoCal Mountains as well. More isolated thunderstorm activity will extend northward into Southern Utah and Southern Colorado, and perhaps the Sierra.

Forecast for Thursday, August 12th

The monsoonal flow will shift east a bit with the heaviest and most widespread rains expected in New Mexico, while Colorado will see more isolated activity and less rainfall. Upslope flow behind a cold front sliding down the east side of the Continental Divide could result in a few thunderstorms across the central and eastern ranges of Montana and Wyoming. Isolated thunderstorms will be possible for the Sierra as well.

Forecast for Friday, August 13th

A cold front moving into Eastern Colorado will result in an uptick in thunderstorms along the Front Range, while activity will also pick up a bit across Western Colorado. More widespread thunderstorms can be expected farther south across New Mexico and Arizona, and an increasing threat for flash flooding can be expected here as well.

A little bit of monsoonal moisture will also sneak into the Sierra and Southern Cascades of Oregon where isolated dry thunderstorms will be possible. Perhaps not the best news for fire danger considering the hot/dry pattern in place along with ongoing fires. 

Forecast for Saturday, August 14th

Widespread thunderstorms with heavy rain and flash flooding potential can be expected across Arizona and New Mexico once again. A little bit of monsoonal moisture will also affect areas from California and Oregon east toward Wyoming and Colorado with generally isolated thunderstorms expected. 

Forecast for Sunday, August 15th

Scattered thunderstorms will affect the Four Corners states on Sunday with more isolated thunderstorms across the Great Basin and Northern Rockies. The flash flooding threat looks lower overall and mainly confined to Southern New Mexico and Southeast Arizona.

A storm system approaching the Pacific Northwest will bring widespread wetting rains to British Columbia on Sunday, and some light showers could reach Western Washington on Sunday night.

Outlook for Mon, Aug 16th - Fri, Aug 20th

Two Pacific storm systems are projected to arrive from the northwest next week as the jet stream dips southward into the Western U.S. These systems will transport a little bit of Pacific moisture, but will also interact with monsoonal moisture to result in a more active pattern across the Rockies with thunderstorms and wetting rains expected at times. 

The European Model (pictured below) is one of the wetter models at this time, but most extended range models are on board with cooler temperatures and elevated rain/thunderstorm potential across the Rockies, while the Northwest including the Washington Cascades should pick up some rain as well.

Thanks so much for reading! Next update on Friday (8/13).

ALAN SMITH

P.S. Could you take a moment to rate the OpenSummit app with a 5-star review? These reviews help us to be seen by more people, and a larger audience provides the support needed for us to build more features and value for you.

Review iPhone app

Review Android app

Simply click either link above and scroll down to the section titled 'Ratings & Reviews'.