This weekendโs colder temperatures will be driven by a sharp drop in the southward jet stream and accompanying cold air over the northwestern United States.
The cold snap could bring mountain snow to parts of the northern Rockies, as well as record low temperatures on the first full weekend of summer in parts of Idaho, Montana and Wyoming, including some national parks during the busiest time of the year.
When will it peak?
This colder weather has moved into the northwest and northern Rockies. It will peak this weekend and last through Monday, possibly Tuesday.
Winter storm warnings are in effect for parts of Montana and Idaho.
How cold will it be?
Some of the coldest places in the northern Great Basin and northern Rockies could see overnight lows drop into the 30s this weekend, Monday or Tuesday. This could be due to daily record lows in several areas of eastern Oregon and Idaho, not to mention summer frosts or freezes in other cold spots at higher elevations.
Even some major cities in the Inland Northwest and northern Great Basin will see morning lows in the 40s this weekend and Monday, including Boise, Reno and parts of Utahโs Salt Lake Valley.
Daytime highs in Seattle, Portland, Spokane and Boise will be much cooler this weekend, either in the 60s or at the very least 70s after scorching heat this week.
But some high-elevation areas of Montana, northwestern Wyoming and Idaho may not see highs rise past the 40s or 50s.
(CARDS: US 10-Day Forecast: Highs and Lows)
Snow in June
This stormier pattern will bring enough cold air to squeeze snow this weekend over parts of the Idaho high country, western Montana and northwestern Wyoming.
We expect snow to fall between 6,000 feet in parts of western Montana and Idaho and up to 8,000 feet in northwest Wyoming.
As you can see in the map below, accumulations of several inches are possible, especially in grassy areas. Some areas saw more than a foot of snow. Ground temperatures on sidewalks and roads are quite warm due to the recent heat wave.
What you need to know
This is a drastic change not only for those sweating from the recent heat, but for anyone vacationing in the northern Rockies, especially those traveling from an area that has either been hot or typically hotter this time of year.
If youโre visiting Yellowstone, Grand Teton or Glacier National Parks this weekend:
- Dress for colder, wetter weather, including a rain jacket, sweatshirts and long pants. Even in areas too warm for snow, cold, driving rain can sometimes fall.
- If you plan to go hiking or camping in the backcountry, dress for winter weather or consider postponing or canceling those plans.
- While some of the snow may melt, some roads over the tops of mountain passes may become slushy or icy, especially at night or early in the morning, including Going-to-the-Sun Road in Glacier National Park, the entire length of which just opened for the summer season to vehicle traffic earlier this week.
- Check national park websites for road and trail conditions based on the forecast.
Itโs not unusual
For most of us, the thought of snow in June would be strange, to say the least.
But this is typical in the northern Rockies and highlands of the Northwest.
We saw June snow in the Mountain West last year, 2023, 2020, 2019, and even July snow in 2016.
Denver has already seen snow in June; Flagstaff, Arizona; Salt Lake City; and Tahoe City, California.
Jonathan Erdman is a senior meteorologist at Weather.com. He has been covering weather domestically and internationally since 1996. Extreme and bizarre weather conditions are his favorite topics. Contact him at bluesky, X (formerly Twitter) And Facebook.