Published: June 9,2017
Snow is in the forecast starting this second weekend of June in the higher elevations of the mountain West, as an unseasonably cold air mass infiltrates the northwestern United States.
The cold air will build in beneath a strong southward dip in the jet stream, or upper-level trough, that will develop this weekend as a result of a weather pattern flip.
(MORE: Heat Wave to Spread Record Highs From Midwest to Northeast Into Early Next Week)
Saturday's Jet Stream Pattern
Temperatures will be 10 to 20 degrees colder than average at times this weekend into early next week, which means it may be cold enough for slushy accumulations of snow in portions of the Cascades and northern Rockies, especially at night. Valley locations won't see highs climb out of the 50s Saturday through Monday.
(MAPS: Weekly Planner)
Snow levels are forecast to fall to between 5,000 and 6,500 feet, lowest in the Washington and Oregon Cascades. Mountain passes in the Cascades are not expected to be impacted, however, as the June sun will make it difficult for snow to accumulate on roadways during the day. Snow is possible down to the Willamette Pass, but impacts are expected to be nil.
Some snow is even possible down to the valley floors in parts of western Wyoming and in most of Yellowstone and Grand Teton national parks by early Tuesday.
Several inches of snow are possible across the highest elevations of the Washington and Oregon Cascades, as well as high mountain locations in Idaho, western Montana, western Wyoming, northeast Utah, northern Colorado, even parts of California's northern Sierra into Tuesday. The best chance of 6-plus inches of snow will be in the Cascades, in northeastern California, and in northwestern Wyoming.
(MORE: Still Up to 40 Feet of Snow on America's Highest Paved Road)
Snowfall Potential Through Tuesday
How Rare is This?It's not uncommon to see snow in the higher elevations of the mountain West this time of year. In fact, it can also occur in valley locations.
Kalispell, Montana, averages 0.3 inches of snow in June, based on data from 1981-2010. As much as 5.5 inches were measured in June 1995.
Great Falls, Montana, also averages 0.3 inches in June, but it saw 11.1 inches of snow back in June 1950.
Just last year, snow accumulated in the northern Rockies as late as July. Snow was reported in parts of Wyoming, Montana and Idaho at elevations as low as 6,500 feet.
(MORE: Winter Rudely Interrupts Summer in the Northern Rockies)