It’s fall, but that hasn’t stopped wild weather from every season from materializing across the Lower 48 this week.
A pair of storm systems — one wet and one white — will drop copious precipitation in the Northeast and High Plains, respectively, with high winds whipping up fire concerns in the West.
Along the battle fronts of the opposing air masses, dramatic temperature swings and powerful storms herald the clashing seasons.
The extreme weather can be traced to a highly energetic October jet stream, the river of roaring high-altitude winds that separates cold and warm air. The jet stream is taking a huge dive over the western United States, accentuating the temperature contrasts in the middle of the nation and powering the High Plains storm.
Flanking this powerful jet stream to the east is the nor’easter set to soak eastern Massachusetts and, to the west, a zone of sinking air surging down the slopes of the mountains and hills in California and creating a high fire danger.
Powerhouse storm in the Mountain West and High Plains
The massive dip in the jet stream in the middle of the nation is inciting a “potentially historic October winter storm” in the Dakotas, as well as tremendous drops in temperature.
One to two feet of snow are possible in parts of the Dakotas through Friday morning, with foot-plus totals spattering the eastern slopes of the higher elevations from Wyoming and northwestern Nebraska up to Montana as well. Winds of 40 to 50 mph could also combine with the moderate to at times heavy snowfall to produce brief whiteouts, with blizzard conditions possible.
Winter storm warnings cover most of the Dakotas, eastern Wyoming and northwest Minnesota.
That premature snowmaker will be powerful enough to shuttle its plume of moisture all the way up to Hudson Bay. In fact, the atmosphere will contain more water vapor in parts of central Canada than in much of Georgia or the Carolinas.
The snowstorm is also dragging a powerful cold front across the Rockies and western Plains, its dramatic temperature contrast flipping the switch from summer to winter in mere hours.
Denver hit 83 degrees on Wednesday; a little over four hours later, it was 41 degrees, with 55 mph winds siphoning in the winter chill as the cold front blasted through. By 10 p.m., it was snowing, just seven hours after the day’s high temperature was set. Extreme temperature plunges are actually a once- or twice-a-year phenomenon for the Colorado High Plains in the fall, but seeing it happen each time with a strong autumn cold front is always remarkable for meteorologists.
As the cold front approached the southern Plains, a sneaky supercell thunderstorm, rotating like a flying saucer, spun up in southwestern Oklahoma. More heavy rain in southeastern Oklahoma can be expected Thursday, along with a slight risk of isolated severe weather.
A super-soaker in the Northeast
Downstream of the big dip in the jet stream in the middle of the nation, a bizarre hybrid storm is developing. It is both intricately connected to the developing snowstorm in the High Plains and linked to the tropics, which is feeding a river of moisture into the storm.
This early-season nor’easter continues to batter the coast of Cape Cod with winds in excess of 55 mph.
While the storm remains far offshore, an expansive wind/rain shield will bring impacts as far west as Interstate 95. Uncertainty exists as to where the heaviest banding sets up in terms of rainfall, but there’s a chance that Southeastern Massachusetts, including Plymouth County, the Cape and islands, could see 3 to 6 inches, or locally more, by Friday.
Western wind storm
Nestled beneath the deep dive in the jet stream that contains the western chill and High Plains snowstorm, high pressure is building into the West. As the clockwise flow around the high-pressure zone forces winds from the east over the hills and mountains in California, the air accelerates down their slopes and dries out, creating dangerous fire conditions.
Red Flag Warnings are plastered over nearly 30,000 square miles in California, where the high winds will bring “critical fire weather conditions” for much of the Golden State.
Recent scant rainfall will combine with warm, dry Santa Ana winds gusting to 50 mph to produce a landscape ripe for ignition. Areas of particular concern include the “Coastal Range, foothills surrounding the Sacramento and Northern San Joaquin Valleys, and mountains of Western Plumas county and the Northern Sierra Nevada,” according to the National Weather Service.
California’s main electric supplier, PG&E, is shutting power to hundreds of thousands of residents as a precaution, barely a year after its lines sparked the infamous Camp Fire. That inferno incinerated the peaceful mountain town of Paradise, claiming 85 lives and forcing the utility company into bankruptcy.
Jason Samenow contributed to this report.