September will end on a cooler and more unsettled note across much of the West. Below-average temperatures can be expected over the next 5 days for many areas, except for most of Wyoming and Montana where temperatures will be above-average.

The week is starting out with a strong storm system impacting the Pacific Northwest on Monday, and a weak but stubborn area of low pressure contributing to unsettled conditions across the Four Corners region.

Rain is already falling over the West Coast, Olympics, and Cascades on Monday morning and will become more widespread on Monday afternoon. A few thunderstorms will be possible as well.

Meanwhile, showers and thunderstorms will also increase in coverage across the Four Corners region on Monday afternoon and evening.

Current Radar

Lightning Density

Forecast Radar

The storm system impacting the Pacific Northwest on Monday will split as it moves inland on Tuesday and Wednesday, with the southern piece of energy diving south into the Four Corners region, resulting in a further uptick in precipitation (including high elevation snow) for Colorado, New Mexico, and portions of Arizona and Utah.

The northern portion of the "split" will quickly weaken with less precipitation expected for Montana and Wyoming as a result. 

Meanwhile, the Pacific Northwest will not see much of a break with another storm system arriving later Wednesday.

The pattern becomes more well-defined on Thursday with a storm system over the Pacific Northwest and a slow-moving storm system continuing to impact the Four Corners and Southern Rockies. 

Forecast for Monday, September 27th

Wet conditions can be expected throughout the Pacific Northwest from Washington to Northern California, and extending eastward into Eastern Washington and the Idaho Panhandle. The West Coast, Olympics, and Oregon Cascades will see the heaviest rain totals.

The Four Corners region will also see extensive coverage of showers and thunderstorms with localized flash flooding in slot canyons and dry washes possible.

Forecast for Tuesday, September 28th

The Northwest storm system will move inland and split apart with widespread showers continuing across the Cascades and Northern/Central Idaho with fewer/lighter showers east of the Montana border. Rain will also become more widespread across Western Colorado along with portions of Utah, Arizona, and New Mexico.

A cold front will also sweep across the West on Tuesday with snow levels falling to 5-6k over the Cascades, 8k over the Central Idaho/Montana, and 10-11k over Utah and Colorado.

Forecast for Wednesday, September 29th

Rain and high elevation snow will continue across Colorado, Southern Wyoming, and Eastern Utah on Wednesday with the focus shifting more toward the Continental Divide/Front Range of Colorado. Farther south, showers will be more scattered in nature across Arizona and New Mexico.

The next storm system will bring more rain and high elevation snow to Western Washington on Wednesday afternoon and Wednesday night.

Snow levels will lower to 9k-10k across the Colorado mountains on Wednesday with light accumulations expected over the Front Range and northern ranges.

Forecast for Thursday, September 30th

The Southern Rockies storm system will meander southward with the heaviest precipitation shifting into New Mexico and Southwest Colorado. High elevation snow should be expected over the San Juan and Sangre de Christo Ranges. 

Heavy precipitation will fall over the Cascades as well, mostly north of the WA/OR border. Lighter showers will extend into Eastern Washington/Northern Idaho but this system will be weakening as it moves inland.

Forecast for Friday, October 1st

Low pressure will linger over the Southern Rockies with significant precipitation expected across New Mexico once again, while Southern/Western Colorado will see lighter rain/snow showers.

The weakening northern system will produce showers across Northeast Oregon, Northern Idaho, and Western Montana with high elevation snow (generally light amounts) expected for these areas as well. The Cascades and Pacific Northwest will see a welcome break in the wet pattern.

Outlook for Sat, Oct 2nd - Wed, Oct 6th

High pressure will build over a large portion of the West this weekend and into early next week with warmer temperatures and drier conditions expected for most areas. The exception will be the Four Corners area, where low pressure is projected to linger for a few (or several) more days with cool and unsettled weather.

The Four Corners region will see the best chance of precipitation during this period, while the West Coast (including the previously wet PNW) and Northern Rockies will be in a drier pattern. 

Thanks so much for reading! Next update on Wednesday (9/29).

ALAN SMITH

We will continue to post the Western U.S. Daily Summit 3x/week through Friday, October 1st.

Starting on Monday, October 4th, we will transition to the US & Canada Daily Snow, at which point we will still talk about impactful weather in the West as needed, but with more of a focus toward snow across North America as a whole as we change seasons.