Even though the official start of the fall season is still several days away with the autumnal equinox at 12:20 PDT on Wednesday, Sept. 22., it seems Mother Nature is getting a little jump on the season in the Northwest.
The changes in the weather that it will usher in will help to ease wildfire concerns, but the rain will not reach everywhere and winds generated by the storm could make matters worse in some locations.
A storm packing drenching rain, much cooler air and even the first snowfall of the season for the high country is on the way for parts of the western United States.
Rain began to soak a portion of western Washington late Thursday night and early Friday morning. As the storm from the Pacific Ocean spirals inland, rain is forecast to reach eastward over the Cascades to parts of the northern Rockies and extend southward into parts of Northern California this weekend.
The storm already pushing into the Northwest has the potential to bring more rain than all of the dry season and the last part of the spring in many areas.
AccuWeather meteorologists expect rain to reach much of the states of Washington and Oregon and even portions of Northern California, northern Idaho and northwestern Montana.
The period from June 15 to Sept. 15 is typically the driest time of the year in the Northwest. Seattle averages a mere 2.95 inches of rain during that three-month stretch, compared to an annual rainfall of 29.34 inches. However, this year, the dry season was extra lean, and the stretch from March 1 to Sept. 8 was the driest in 77 years, with only 6.78 inches of rain or 54% of normal, according to the National Weather Service in Seattle. During this year’s dry season, the three-month stretch from June 15 to Sept. 15, only 0.26 of an inch of rain fell at Seattle-Tacoma International Airport.
“A general 1-2 inches of rain is forecast in the zone in between the Coast Ranges and the Cascades in Washington and Oregon, with 0.25 to 1.00 inch of rain possible east of the Cascades in Washington, Oregon and northern Idaho,” AccuWeather Senior Meteorologist Brett Anderson said.
“Heavier rain is forecast along the western slopes of the Olympics, Coast Ranges and Cascades,” Anderson stated. In these areas, a general 2-4 inches of rain is expected with an AccuWeather Local StormMaxâ„¢ of 8 inches.
Owl Mountain, Washington, on the Olympic Peninsula, has already racked up 3.03 inches of rain on Friday, with Sekiu, Washington, close behind with 2.61 inches.
Rain may stop short of drenching San Francisco, but rain is forecast to soak areas farther to the north in the Golden State. Redding, California, is among some of the major cities expected to pick up at least a few hours of rain from the storm system.
Pendleton, Oregon, Spokane, Washington, and Boise, Idaho, are among the cities across the interior Northwest that should receive some soaking rain.
And as temperatures drop off, rain is not the only form of precipitation on the way for the western U.S. The first snow of the season is in the offing for parts of the high country of the West.
“A rain and snow mix can occur over some of the passes in the northern and central Rockies with some accumulation beginning above 6,500 feet in elevation,” Anderson added.
In some of the lower elevations, gusty thunderstorms may precede and mark the arrival of cooler air, including in parts of the Great Basin on Saturday.
In Aspen, Colorado, on Tuesday morning, temperatures are forecast to dip below freezing for the first time since May 25. Following high temperatures in the mid-90s in Denver during the latter part of this week, highs in the 70s and nighttime lows in the 40s will make it feel like fall just in time for the official change in seasons early next week.
The early blast of autumn will come as parts of the region are already showing tell-tale signs of the seasonal transition. The Aspen trees in parts of the Colorado Rockies have already transformed with stunning hues of amber and yellow.
In order for there to be snow over the high country, temperatures have to tumble. A plunge of 20, 30 and even 40 degrees Fahrenheit is forecast into early next week. For example, high temperatures in Salt Lake City have peaked in the middle to upper 80s during the second half of last week, but even in the basin where the city is situated, highs are forecast to be in the mid-60s on Monday. Nighttime, low temperatures are predicted to be in the middle 40s during the last couple of nights of the summer.
“Winds can gust past 50 mph over some of the passes and along the eastern slopes of the mountain ranges,” Anderson said. The windiest conditions along and just east of the Rockies are likely to unfold Sunday and Sunday night, he added.
Winds will pose a problem ahead of any rain and in areas south of the storm both in terms of spreading any existing wildfires and raising the risk of new wildfires igniting as burning embers are whisked along.
Accompanying the snap to cooler conditions, areas of rain and high country snow will be gusty winds.