Great Falls, Montana — A dramatic weather reversal is coming to the western United States, with temperatures expected to plunge by as much as 25 to 50 degrees Fahrenheit in some locations as a deep dip in the jet stream sends much colder air across the region.
The sharp change will arrive after a stretch of unusually warm weather, including temperatures approaching the upper 90s and even 100 degrees in parts of the West. By this weekend and early next week, conditions will look much more like late autumn, with snow developing across portions of the Rockies and northern mountain ranges.
The dramatic shift will stretch from Washington and Montana to California and the northern Plains, bringing an early taste of winter to some higher elevations.
Montana Temperatures Could Collapse
Great Falls is expected to experience one of the most noticeable temperature swings.
After temperatures climb into the 80s on Tuesday, highs are expected to remain mainly in the 70s through the rest of the week before falling sharply this weekend.
By Sunday and Monday, temperatures could reach only the 30s during the afternoon.
That represents a remarkable reversal in just a few days, especially after the region recently experienced much warmer conditions. South Dakota will also experience a major change.
Rapid City could see temperatures challenge record highs in the low 90s as late as Friday, but by Sunday, afternoon temperatures are expected to remain in the 50s or lower.
Spokane and California Will Feel the Chill
The cold air will not be confined to the northern Rockies.
Spokane, Washington, could struggle to reach 50 degrees Sunday afternoon, a dramatic departure from the warmer weather experienced earlier in the week.
Farther south, cities that have experienced temperatures near 100 degrees will also notice the difference.
Sacramento, Los Angeles and Las Vegas are all expected to turn considerably cooler this weekend. After periods of near-100-degree heat this week, afternoon temperatures could generally remain in the 70s by Sunday.
The sudden reversal will be especially noticeable for residents who have been enjoying summer-like weather well into the fall.
Tropical Moisture Will Meet the Cold Air
The incoming cold air will arrive alongside another important ingredient: tropical moisture. A deepening dip in the jet stream is expected to combine with moisture moving northward later this weekend into early next week. Some of that moisture will be associated with Hurricane Rachel in the eastern Pacific.
The combination of cold air and abundant moisture will help create conditions favorable for widespread precipitation.
Rain is expected to fall across portions of the Colorado and Snake River basins, while snow levels drop across several western states.
Snow Could Spread Across the Rockies
As colder air moves in, snow levels are expected to fall across Washington, Oregon, California, Idaho and Montana this weekend.
By early next week, the snow threat will expand toward Wyoming, Utah, Colorado and the Dakotas.
Higher elevations will be particularly vulnerable to accumulating snow, creating potentially difficult travel conditions in mountain areas.
Glacier National Park is expected to see heavy snow later this weekend, while some intermediate and higher elevations around Yellowstone National Park could also receive accumulating snowfall.
For outdoor enthusiasts and travelers, conditions could change quickly as temperatures fall and snow develops.
Mountain Passes Could See Rain and Snow
Not every location will immediately turn snowy.
Parts of the Washington Cascades could see rain mixed with snow from late Friday into early Saturday, but significant accumulation is not currently expected around the passes.
A similar situation is expected near Lake Tahoe, California, where rain and snow could mix later Sunday into Sunday night. Nearby Donner Pass is expected to remain primarily wet rather than seeing significant snow accumulation.
The distinction will be important for travelers because temperatures can vary considerably between lower valleys and higher mountain elevations.
Western Weather Is About to Change Dramatically
The coming pattern represents one of the sharpest weather transitions of the season so far.
Communities that are still experiencing summer-like heat this week could be dealing with temperatures more typical of late fall by Sunday.
The combination of a plunging jet stream, rapidly falling temperatures and tropical moisture could also make the weather increasingly unsettled across the West.
For residents and travelers, the biggest changes are expected over the weekend and into early next week, when the coldest air and expanding snow threat arrive.
Are you ready for the sudden temperature drop? If you’re in the western U.S., tell us your city and what temperatures you’re expecting this weekend in the comments.
