Forecast Highlights:

• Heavy snow for Alaska above 4,000-5,000 feet, especially on Thursday and Friday.
• Light snow for the Canadian Rockies and Northern U.S. Rockies along and east of the Continental Divide from Thursday to Saturday.
• Heat wave continues across the West on Wednesday, before gradually relenting for most areas in the days to follow (Central/Northern California excluded).
• Smoky conditions across much of the West can be expected for the rest of this week and over the weekend due to active fires across Idaho, the Northwest, and California. 
• Rain for the Southwest & SoCal late this week through early next week along with cooler temps due to moisture arriving from the remnants of Hurricane Fay.
• Wet pattern for the Southern Appalachians with heavy rain late this week and over the weekend, with lighter/less frequent showers for New England.

Alaska Snow:

The seasonal transition is well underway up north as a series of storms will bring heavy precipitation to Alaska over the next 5 days, including heavy snow above 4,000-5,000 feet where 1-2+ feet will be possible over the next 5 days. The heaviest snow is expected on Thursday and Friday, and snow levels could even drop as low as 3,000 feet early on Friday.

Lower 48 and Canada – Summer Hangs on, but some signs of cooler times ahead:

The big story over the past week has been a record-setting heatwave across Western North America that has shattered all-time record highs for the month of September in many locations.

Unseasonably hot temperatures (with more records possible) will continue on Wednesday, then we will gradually see the heat relent in the days to follow, except for Northern/Central California where the heat will persist a bit longer. The coolest air arriving will occur near and east of the Divide in the Northern Rockies, where some light snow can be expected across the higher elevations.

Across the East, an area of low pressure over the Southeast will supply copious amounts of moisture into the Southern Appalachians where heavy rain can be expected over the next several days, while the Northeast & New England will see drier conditions with only occasional light showers.

Looking further out, keep an eye on the Southwest U.S. including Southern California, where moisture from Hurricane Fay in the Eastern Pacific will arrive, resulting in a wetter pattern with moderate to locally heavy rain possible. 

Western U.S. Smoke Update:

Most of the summer was relatively quiet in terms of widespread smoke across the West, but that has changed recently thanks to the record-setting heatwave, which has contributed to a significant uptick in fire activity. 

Idaho is the main hot spot for fires right now, while Washington, Oregon, and California are experiencing some large fires as well. Smoke from these fires will impact much of the West on Wednesday, with west/southwest winds aloft (winds blowing from this direction) resulting in the heaviest smoke conditions across the Northern Rockies.

From Thursday through the weekend, winds aloft will transition to blowing out of the northwest, which will transport more of the smoke further south into the Central Rockies. Below is the smoke projection for Thursday afternoon, and I would expect a further uptick in smoke across parts of Utah and Colorado in the days to follow with a decrease in smoke across Canada.

For down-to-the-hour smoke projections, be sure to check out our Smoke Forecast Map for Days 1-2, and our Air Quality Forecast Map for Days 3-5. Also, we have a Current Air Quality Map which shows air quality index ratings from sensors throughout North America.

Forecast for Wed 9/7 – Thu 9/8:

A storm will impact Southeast Alaska during this period with heavy mountain snow expected, especially on Thursday. A cold front will also slide in from the north on Thursday with light snow expected across the Canadian Rockies.

As the cold front approaches, rain will develop across the Northern U.S. Rockies, favoring areas along and east of the Divide in Montana and Northern Wyoming. By later in the day on Thursday, the higher peaks in this area will also start to see a change-over to snow.

Across the East, showers and thunderstorms can be expected from the Southern Appalachians to New York on Wednesday with the heaviest rain expected across the Allegheny Range in Pennsylvania. Thursday is looking a bit drier in the East with lighter showers. 

Forecast for Fri 9/9 – Sat 9/10:

The higher elevations of Alaska will continue to see heavy snow during this period. Meanwhile, areas along and east of the Divide in the Northern Rockies will also pick up some light snow on Friday and early Saturday. This includes Glacier NP as well as the Beartooth, Bighorn, and Wind River Ranges. The higher peaks of Colorado could also see some light snow on Friday night and Saturday.

Moisture from the remnants of Hurricane Fay will also reach the Southwest U.S. during this time where more numerous showers and thunderstorms will develop, including the potential for heavy rain and flash flooding across Arizona and Southern California.

Across the East, a cold front will result in heavy rain across the Great Lakes on Friday and Saturday, while the next surge of Gulf moisture will result in heavy rain and possible flash flooding across the Southern Appalachians on Friday night and Saturday.

Forecast for Sun 9/11 – Mon 9/12:

Alaska will see somewhat of a break in the pattern with only some light snow expected across the higher elevations during this period. Otherwise, no snow is expected anywhere else in the mountainous regions of North America on either day.

Showers and thunderstorms will continue across the Southwest during this period, with some of this activity potentially expanding into the Pacific Northwest and Northern Rockies. A slow-moving area of low pressure with abundant Gulf moisture will also result in heavy rain across the Southern/Central Appalachians and Southern Great Lakes.

Outlook for Tue 9/13 – Sat 9/17:

An active storm track and snowy pattern looks to resume across Southeast Alaska during this period with additional heavy accumulations possible across the higher terrain.

Meanwhile, the Western U.S. will see a welcome change to a cooler and wetter pattern with near to below-average temperatures expected for a change across much of the region. A trough of low pressure setting up near the West Coast will tap into lingering subtropical moisture to result in more widespread showers and thunderstorms, favoring the Great Basin and Central/Northern Rockies.

Toward the end of this period, as cooler air sets in, it's possible the higher elevations of the Northern Rockies could pick up a little bit of snow.

Another good thing about this cooler/wetter pattern across the West is that fire activity and behavior should decrease, and smoke conditions should start to improve as a result.

Across the East, the wet pattern that was present over the Southeast will shift into the Northeast and New England where more abundant rainfall can be expected along with cooler temperatures. The Southern Appalachians will transition into a drier and warmer pattern. 

Thanks so much for reading! Next update on Wednesday (9/14).

ALAN SMITH

Thinking ahead to winter?

Check out our recent article re: the latest La Nina update and what it could mean for ski season!

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