Fresh snow on Mt. Hood, OR on June 16th, 2016.
© Timberline lodgeFresh snow on Mt. Hood, OR on June 16th, 2016.
At the height of summer, snow is forecast to blanket the high terrain of the northwestern U.S. this weekend and early next week.

"It is July right?" asks the National Weather Service forecast office in Medford, Ore., which then advises: "Get ready for a significant change . . . Snow levels will drop down to 6000 ft. Saturday night and 1-3 inches will be possible in the high Cascades above 6000 ft., including Crater Lake Rim."

The fresh snow is sure to delight summer skiers on Mount Hood, where skiing is possible year-round. "Timberline Lodge on Mt. Hood is still open daily and they'll be having themselves a nice mini powder day tomorrow [Saturday]," writes the ski portal SnowBrains.com.

Snow is forecast continuously through Monday on Washington state's Mount Rainier, which ascends to 14,410 feet.

The unseasonably chilly air shifts east early next week, when high peaks in Montana, Wyoming and Idaho could also see the white stuff. The Weather Service office in Glasgow, Mont., says an inch or so is possible above 8,000 feet Sunday night into Monday, although some model simulations suggest the possibility of several inches.

Temperatures may be an astonishing 30 degrees colder than normal in parts of southwest Montana, eastern Idaho and western Wyoming on Monday.

Temperature difference from normal predicted by GFS model at 11 a.m. western time Monday
© WeatherBell.comTemperature difference from normal predicted by GFS model at 11 a.m. western time Monday
A deep area of low pressure at high altitudes and its associated pool of chilled air is to blame for the spell of winter-like weather.

GFS model forecast of high altitude weather pattern shows deep area of low pressure at 18,000 feet (500 mb) late Sunday.
© WeatherBell.comGFS model forecast of high altitude weather pattern shows deep area of low pressure at 18,000 feet (500 mb) late Sunday.
It is forecast to retreat into Saskatchewan by the middle of next week.

Although the Weather Service office in Medford is calling the responsible weather pattern "very unusual," July snow at high elevations in the northwest United States isn't unheard of. Just last July, several inches of snow blasted the Northern Rockies following the passage of an exceptionally strong cold front.