A blast of unseasonably cold air, gusty thunderstorms and mountain snow will spread across the West this weekend into next week.
A strong push of cool air will erase the buildup of warmth in the coastal Northwest prior to the end of this week. However, much colder air will soon follow and expand across more territory in the West.
"The pattern coming up for this weekend into early next week in the West is like a forgotten piece of March or early April," according to AccuWeather Long-Range Meteorologist Paul Paselok.
The chill and wintry weather will only be negated by the time of the year and the effects of the June sun.
"People heading to the mountains for rafting, hiking or camping trips should be prepared for wintry conditions in the high country and out of season chill at lower elevations," according to AccuWeather Senior Meteorologist Henry Margusity.
Temperatures will be slashed by 20 to 40 degrees Fahrenheit from their peak levels this week.
Over the mountains, temperatures will plunge into the 30s and lower 40s during daytime rain and snow showers with lows at night possibly dipping into the 20s.
"The wintry weather will first hit the Cascades late this week and the northern Sierra Nevada with lowering snow levels this weekend," Margusity said.
Snow levels may dip below 5,000 feet in the Cascades and to near 6,500 feet in the northern Sierra Nevada this weekend.
The snowiest spots of the high country may receive several inches of snow. The combination of gusty winds and heavy, wet snow may cause tree limbs to break, which may not only be a hazard for campers and hikers, but could block some back mountain roads.
Even at lower elevations to the Pacific coast and in parts of the deserts, there will be the potential for locally heavy, gusty thunderstorms with hail.
The risk for thunderstorms and then mountain snow will spread southward and eastward this weekend into early next week.
It is possible the same weather pattern will hit parts of the northern and central Rockies just as hard.
"People heading to Yellowstone and Glacier National Park may want to keep checking for forecast updates for the potential for severe weather, followed by a possible wet snow blizzard early next week," Margusity said.
Ahead of the dramatic change to chilly conditions, this week's surge of heat is causing significant snowmelt in the mountains.
This surge of hot weather is causing streams and rivers flowing out of the mountains to rise to near bank full.
"While the high water is a boon for white water interests, it can pose dangers due to the highest flow rates in decades in some cases," according to AccuWeather Senior Meteorologist Ken Clark.
"An added concern is for cold water shock, since the runoff is mostly from melting snow," Clark said.
Symptoms of cold water shock include gasp reflex, hyperventilation, difficulty holding your breath, rapid heart rate and elevated blood pressure. Following these symptoms, muscle cramps, hypothermia, drowning or cardiac arrest can occur.
Hypothermia can occur in any water temperature below 70, according to the Centers for Disease Control and Prevention (CDC).
The chilly air will slow the rate of snowmelt for only a brief time.
"Following the unseasonable chill this weekend into early next week, temperatures will strongly rebound west of the Continental Divide and along the Pacific coast later next week," Pastelok said. "However, temperatures may be slower to rebound farther east near the Rockies."