A sharply colder weather pattern could bring mountain snow to parts of the northern Rockies, along with some record cold temperatures for the first full weekend of summer to parts of Idaho, Montana and Wyoming — including some national parks during their busiest time of year.

When will it arrive?

This colder weather will first move into the Northwest and northern Rockies Friday, peak this weekend, and linger into Monday, perhaps Tuesday.

How cold will it be?

Some of the coldest places in the northern Great Basin and northern Rockies could see nighttime lows plunge into the 30s this weekend into Monday or Tuesday. That could flirt with daily record lows in a few areas of eastern Oregon and Idaho, not to mention a summer frost or freeze in other higher elevation cold spots.

Even some larger cities of the interior Northwest and northern Great Basin will see morning lows dip into the 40s this weekend into Monday, including Boise, Reno and parts of Utah's Salt Lake Valley.

Daytime highs in Seattle, Portland, Spokane and Boise will be much cooler this weekend in either the 60s or at most low 70s after this week's searing heat.

But parts of the high country of Montana, northwest Wyoming and Idaho may not see highs rise out of the 40s or 50s.

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

Snow in June

This stormier pattern may have just enough cold air to wring out snow this weekend over parts of the high country of Idaho, western Montana and western Wyoming.

We expect snow to fall at elevations as low as 6,000 feet in parts of western Montana and Idaho and to 8,000 feet in northwest Wyoming.

As you can see in the map below, several inches of accumulation are possible, especially on grassy areas. Ground temperatures on pavement and roads are quite warm from the recent heat.

What you need to know

This is an abrupt change, not only for those sweating through recent heat, but also anyone vacationing in the northern Rockies, especially those traveling from an area that either has been hot or is typically hotter this time of year.

If you're visiting Yellowstone, Grand Teton or Glacier national parks this weekend:

• Dress for colder, wetter weather, including rain gear, sweatshirts and long pants. Even in areas too warm to snow, a cold, raw rain could fall, at times.
  
• If you plan on camping or hiking in the backcountry, dress for winter weather or consider delaying or canceling those plans.
  
• While some falling snow may melt, some roads over mountain pass summits could become slush or ice-covered, especially at night or early in the morning, including the Going-to-the-Sun Road in Glacier National Park, whose full length just opened for the summer season to vehicle traffic earlier this week.
  
• Check national park websites for the status of any roads or trails, given the forecast.
  

This isn't unusual

For most of us, the thought of snow in June would be bizarre, to put it mildly.

But in the northern Rockies and Northwest high country, it's typical.

We've seen June Mountain West snow last year, in 2023, 2020, 2019 and even July snow in 2016.

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

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.