Summer snow? Here's where it's in the forecast.

Summer snow is forecast to blanket portions of the northern Rockies by the weekend of June 27, forecasters said.

Overall, after a hot start to the week, much of the West is in line for a major cool-down by the end of the week and into the weekend, according to NOAA's Weather Prediction Center (WPC).

A relatively potent cold front for this time of year will cross the Pacific Northwest and Intermountain West, the WPC said. The cold front will bring relief from the heat starting Friday, June 26, and will become even more noticeable going into the weekend as highs return to below average by late-June standards.

Shift in the weather pattern

A significant shift in the weather pattern is expected this weekend (June 27-28), bringing much colder temperatures, widespread rain, and high-elevation snow to the region, the National Weather Service in Missoula, Montana, said in a June 23 online forecast.

Rain will be the story for some areas: "Confidence is high (>90%) for widespread rain across the area, with over an inch possible across higher terrain and along the [continental] divide," the weather service said.

In the mountains, snow will be likely into Sunday, June 28, the weather service said. High temperatures will be unseasonably chilly, with valleys struggling to get out of the 50s and 60s, while higher terrain will stay in the 30s and 40s.

"Those with outdoor or recreation plans, particularly in the backcountry, should prepare for a heightened risk of hypothermia and monitor the forecast closely as the weekend approaches," the weather service said.

Falling snow levels

Falling snow levels from Saturday night, June 27, through Sunday, June 28, will bring the opportunity for accumulating snow to the mountains. Snow levels will drop to around 7,000 feet on the mornings of Sunday, June 28, and Monday, June 29, bringing accumulating snow to the higher terrain.

Sunday, June 28, appears to be the coldest day as afternoon readings will be around 20 degrees below seasonal averages.

Heat dome in the East?

While the West cools down, the opposite will be true in the East by next week, as a large area of high pressure is forecast to set up shop over the eastern half of the United States.

Weather Trader meteorologist Ryan Maue, in an e-mail to USA TODAY, said that the high pressure area in the East could develop into a heat dome, which means warmer than normal temperature into the 4th of July east of the Rockies.

Doyle Rice is a national correspondent for USA TODAY, with a focus on weather and climate.