Winter storm warnings have been posted in parts of Montana as snow will blanket parts of the northern Rockies and Cascades this first weekend of summer.

It sounds like something the late New York Yankees catcher Yogi Berra might have once said: a "summer winter storm". But it's in the forecast this weekend.

Let's start with the forecast details, then examine if this is really unusual.

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NWS Alerts

- Winter weather advisories for generally light snow accumulations are in effect for some higher elevations in western Montana, as shown in the map below.

- For areas farther north near Glacier National Park in northwest Montana, winter storm warnings have been issued for heavier accumulations.

Snow Details

- The bulk of this snow will fall from by Sunday morning, though snow could start earlier farther north near Glacier National Park.

- Near Glacier National Park: Snow totals could top out at 12 to 18 inches at elevations above 6,000 feet, according to the National Weather Service.

- Rest of northern Rockies, Cascades: At least a couple inches of snow could fall at elevations as low as 5,000 feet.

(MAPS: 10-Day Forecast US Highs/Lows)

Potential Impacts

- This could lead to at least some slushy travel over mountain passes, especially by Sunday morning. That could prompt the closure of at least a section of the Going-to-the-Sun Road in Glacier National Park, which was finally fully opened for the season last Monday.

- The combination of this heavy, wet, late-season snow and wind could lead to some downed trees and power outages, as well.

- It will also be quite chilly, with some lows in the 30s Sunday and Monday morning.

How Weird Is This?

- June snow is not unusual for the Rockies.

- Snow has fallen in June before in Denver; Flagstaff, Arizona; Salt Lake City and Tahoe City, California.

- We've seen June Mountain West snow in 2019, 2020, and 2023. It's even happened in the northern Rockies recently in July 2016.

Why It's Happening?

- The same pattern responsible for a blistering heat wave in the Plains, Midwest and East is helping wring out the June snow in the West.

- As the map at the top of this article shows, the jet stream is taking a sharp U-shaped plunge into the Northwest.

- That's providing the moisture and lift in the atmosphere for precipitation. And it's also injected just enough cold air to turn that precipitation into snow over the higher elevations.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.