A pattern change is coming for the western U.S. starting Thursday and lasting through next week.

A strong storm system will dive southward out of Canada and into the northern U.S., bringing chilly air, rain and mountain snow into the northern Rockies Thursday into Saturday

This will break the hot and dry stagnant pattern that has plagued this part of the U.S. over the past couple of weeks and arguably most of the summer.

A pattern change is expected with a trough setting up in the West (dip in lines and blue shading) and a ridge setting up in the East (rise in lines and orange shading). This will favor cool and unsettled conditions for the Northwest. Image shown is GEFS 500 mb mean height anomalies a week out from Wednesday Sept. 13.

Rain will begin Thursday morning but will increase in coverage and intensity by Thursday night, lasting into Saturday. This will occur across Montana, Idaho, Wyoming and northern Colorado and Utah. A lot of areas will see 0.50 inch of rain to up to 1.50 inches of rain.

A shot of cold air will be delayed at first but will arrive early Friday changing rain to snow for elevations as low as 6,000 feet. Snow amounts will vary but general amounts will be 6 inches to a foot and a half across the highest elevations of Montana, Idaho and Wyoming.

This will be the first snowfall of the season for a lot of the northern Rockies, including Yellowstone and Glacier National Parks.

A storm of this magnitude diving this far south for mid-September is slightly early but these storms will become more frequent as we head through late September and October.

The rain and snow could not come soon enough. According to the National Interagency Fire Center, 62 active large fires are burning across the West. Montana (20) and Oregon (17) account for over half of those.

Numerous wildfires have created smoke-filled skies across the Northwest over the past few weeks. This image is from Sept. 6.

Acres burned so far this season is above 8 million and ranks third since 2006. The average through Sept. 12 is just under 6 million.

Many states in the West are desperate for water and this storm will deliver some relief to at least a few.

As I mentioned at the top, there are signs that this pattern will continue through next week. Models are in agreement of a strong storm diving into the Pacific Northwest around Monday and Tuesday which would bring some rain and cooler air.

Models are in agreement that another powerful storm system will arrive in the Pacific Northwest early next week. This would favor more cool and unsettled weather for the Northwest. Image shown is GEFS 500 mb height anomaly for late Monday.


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