Over the weekend snow fell and accumulated over the high elevations surrounding Lake Tahoe, CA and in the Rockies west of Denver.

The below picture taken just this morning shows a rather wintry scene at the Arapahoe Basin Ski Area to the west of Denver. A few inches also fell as Berthoud Pass and several other high elevation areas also saw their first snows of the season.

Over the next 24 to 48 hours, the first significant storm of the season is set to slam into the Pacific Northwest bringing heavy rain and strong winds but this system also has a wintry side and all models point to a rather wintry side.

The system that brought Anchorage, Alaska it’s first snow and snow to Fairbanks overnight which created icy roads just this morning along with gales to the south coast, looks set to bring a good few inches of rain to the British Columbia and Washington coast. The storm will also drag in unseasonably cold air.

Here’s the upper level chart for tomorrow off the GFS operational model.

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Notice during tomorrow, the system can be seen approaching the coast but by Wednesday (below), the upper trough is being carved out with heights falls and the freezing line falling.

By this point, heights rise over the Plains and Midwest with temperatures rising back into the 80s, even 90s.. after all it is only September still right?

By Thursday the system is crossing the Northern Rockies and while wind and rain affects a large area, above say 5,000ft, precipitation will begin turning from rain to snow as colder air feeds in on the backside of the low.

While temperatures rise over the Plains, Midwest and Ohio Valley, the upper low remains stubborn to clear Newfoundland and so temperatures and weather won’t be just as nice here with a much cooler, fresher air flow coming out of Quebec and not the Midwest.

By Friday, while high pressure begins to build into the Pacific Northwest, the trough axis will be firmly over the Great Basin extending into the Rockies where it will be cold, windy and above 4,500ft, snowy! Expect the first significant snowfall for parts of Montana and Wyoming, particularly the Yellowstone area as well as Colorado and the Upper Benches of Utah where upwards of 3-6 inches is possible, even a foot in the highest elevations.

The ECMWF 500mb chart and 850 temps correlate well with the GFS operational and you can see clearly the large spread in heights and 5,000ft temps between the Northern and central Rockies and Midwest where temperatures are likely to be 40 to near 50 degrees in difference in spots.

Notice in the GFS upper charts both Thursday and Friday how the ridge pokes it’s nose into the Midwest and Great Lakes with a stiff southwest wind blowing ahead of the front. Couple that with dry ground and temperatures may climb into the mid, even upper 80s in cities such as St Louis and Chicago. What a contrast that would be to the 30s and 40s over the Intermountain West where snow may be falling heavily and driven by a strong, gusty wind.

Here’s the GFS projected snowfall now through Friday and you can see the snows that are expected.

As for precipitation, plenty of moisture streams into the Pacific Northwest along with wind gusts along the coast and ridges to between 50 and 60 mph.

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Tags: First snows arrive in Rockies, Rockies snowstorm, september snow