Last week's heatwave was another blow to what has been a frustratingly hot and smoky summer for most of the West. The good news is that we have a major change on the way this week as a fall-like low-pressure system arrives. This will bring a reprieve to the hot and dry conditions, and to some extent, the smoke.

Taking a look at the projected large-scale pattern for late Monday afternoon, we can see a trough of low pressure over British Columbia pushing across the border into Washington. This will be our "weather maker" this week. 

By mid-week, this system will strengthen into a large area of low pressure and set up over the Great Basin. This system will tap into both Pacific moisture and monsoonal moisture with downstream impacts over the Rockies, and much colder air will also be arriving.

The system will eventually get moving and swing east of the Rockies later on Friday, but then a secondary disturbance will approach, leading to more unsettled weather and below average temperatures for the Northern Rockies heading into the weekend.

Over the next 5 days, temperatures are expected to be below average across a significant portion of the West. This is the most "blue" we've seen on one of these 5-day maps in quite some time!

As of Monday afternoon, an active monsoon pattern remains in place across the Southwest with thunderstorms ongoing across New Mexico, Arizona, Southeast Utah, and the San Juans in Colorado.

As the low pressure system approaches, moisture and energy downstream of the system will lead to a noticeable uptick in thunderstorms and wetting rains across Utah on Tuesday afternoon.

This system will also result in widespread showers and thunderstorms up north in Montana, British Columbia, and Alberta on Tuesday.

Current Radar

Lightning Density

Forecast Radar

Wildfire and Smoke Update

Smoke from fires in California, Oregon, Washington, and British Columbia continues to impact a large portion of the West on Monday. Check out our smoke forecast map for early Monday evening, which provides a good visual of approximate fire locations and where the associated smoke is impacting.

As a powerful storm system moves into the Western U.S. over the next couple of days, many areas will start to see an improvement in the smoke situation, with the worst smoke conditions confined to areas close the fires.

Here is the smoke forecast for Wednesday morning:

Forecast Smoke (surface)

Forecast Smoke (sky)

Current Air Quality

My confidence is low in the smoke outlook for the remainder of the week (from Wednesday afternoon on), so be sure to keep up to date with the latest smoke forecasts on the OpenSummit map overlays.

I do think the storm system setting up over the West will lead to overall improvement in smoke across the Rockies, but that doesn't mean we couldn't see some smoky stretches from time to time if smoke from California fires becomes entrained into the flow around the low pressure center.

The worst smoke conditions can be expected near the fires from California to British Columbia. Some areas in the northwest could see a reduction in fire activity depending on how much rain falls. At the very least, higher relative humidity and cooler temperatures will help.

Forecast for Monday, August 16th

Thunderstorms with heavy rain can be expected across Arizona and New Mexico with more isolated thunderstorms elsewhere across the West. Showers and thunderstorms will impact British Columbia and Alberta as well with light showers dipping south into the Washington Cascades on Monday night.

Forecast for Tuesday, August 17th

Widespread rain and thunderstorms will develop across Western Montana on Tuesday with showers developing across portions of Idaho and Northeast Washington as well. Lighter showers will occur farther west over the Cascades. As colder air arrives, the higher elevations of Glacier National Park could see some snow – with even better odds of snow farther north across the Canadian Rockies.

Farther south, energy ahead of this system will interact with monsoonal moisture to result in an uptick in thunderstorms and wetting rains across Utah (including the Wasatch) and Arizona. In fact, Flash Flood Watches have already been issues for many mountain and canyon areas of Utah.

Forecast for Wednesday, August 18th

Widespread rain and thunderstorms can be expected across a large portion fo the Northern and Central Rockies with the heaviest amounts expected in Utah, Western Colorado, Wyoming, and Southwest Montana. The flash flooding threat could be significant across a large portion of Utah.

Colder air arriving from the west will likely result in some snow flying across the higher peaks of the Sawtooths, Tetons, and Uintas as well as Glacier National Park. All across this region, cold and wet backcountry conditions should be expected.

Forecast for Thursday, August 19th

Slow movement of the storm system will continue to result in abundant rainfall and chilly temperatures across the Central and Northern Rockies. The heaviest rain amounts can be expected across Utah, Western Colorado, Wyoming, and Southwest Montana once again.

High elevation snow (generally above 10k or 11k feet) should be expected at times across the Teton, Madison, Gallatin, Wind River, Beartooth, Bighorn, and Uinta Ranges.

Forecast for Friday, August 20th

The storm system will finally begin to swing east later on Friday, but backside showers will continue across Northwest Wyoming and Southwest Montana with more isolated showers and storms farther south in Utah and Colorado.

Late Friday afternoon and into Friday night, the next round of showers will arrive across northern portions of Washington, Idaho, and Montana as a second weaker storm system approaches.

Outlook for Sat, Aug 21st - Wed, Aug 25th

The mentioned second storm system will impact the Northern and Central Rockies over the weekend with additional showers and thunderstorms along with cooler than average temperatures. Some models are also projecting a trailing disturbance that could keep unsettled conditions going into early next week, before drying out mid-week.

Farther south in Arizona and New Mexico, the monsoonal flow will weaken thanks to the series of storm systems passing to the north – but enough moisture should remain for isolated thunderstorm chances and lighter rainfall.

Precipitation is not expected to devitate much from average during this five-day period. Rain and thunderstorm chances will exist from north to south across the Rockies and canyon/desert regions, but significant rainfall is not anticipated at this time. Temperatures are expected to be cooler than average up north and warmer than average in the south.

Thanks so much for reading! Next update on Wednesday (8/18).

ALAN SMITH

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