This new storm slamming the West has prompted the National Weather Service to hoist advisories for multiple hazards affecting tens of millions of people from California to Colorado.
The powerful system will drop up to two feet of snow in the central and northern Rockies, while summerlike warmth spreads out ahead of it to the East. In between, the seasons will wage war, spelling dangerous storms and possible flooding on the Plains for Tuesday into Wednesday.
Brewing the meteorological maelstrom is an active jet stream slicing across the country. It dips in the west, allowing frigid air at high altitudes to spill south from Canada.
The serious California wind and fire threat
A cold front is cutting through California along the leading edge of the dipping jet stream, drawing bone-dry air southward and a surge of winds.
Meteorologists often refer to the pattern as an “inside slider” because the jet stream, instead of moving in directly from the Pacific Ocean, will dive farther inland and bring mostly wind instead of rain.
“It places all of coastal California in that drier environment,” said Gerry Díaz, a meteorologist with the Bay Area National Weather Service in Monterey, Calif.
Despite chilly temperatures, Díaz said, there is still concern that any new ignitions could spread rapidly given the gusty winds, low humidity and ongoing drought conditions. Nearly 90 percent of California remains in extreme to exceptional drought, according to the latest U.S. Drought Monitor.
Red flag warnings for high fire danger have been posted through Tuesday for much of northern and central California. However, the strongest winds are expected Monday, when high-wind advisories are in effect. Weather offices are warning of possible downed trees, power outages and difficult driving conditions.
Pacific Gas and Electric plans targeted power shut-offs for approximately 25,000 customers in 22 counties “to reduce the risk of wildfire from energized power lines.” Southern California Edison was considering cutting power to about 9,000 customers in Los Angeles and Ventura counties.
The winds will be fierce through the Central Valley, where air funnels easily between the coastal ranges and the Sierra Nevada, but will also overspread the Bay Area, Central Coast and Southern California. Widespread gusts of up to 50 mph are expected, while the highest peaks in the Bay Area could see gusts exceeding 60 mph. The Los Angeles region will also see potentially damaging winds and elevated fire weather.
The weather system is expected to impact the Windy Fire, which is burning through sequoia groves in the Sequoia National Forest. Although the 97,000-acre blaze is 88 percent contained, there could be a significant increase in fire behavior Monday, with wind-driven runs, according to an Inciweb report.
Cindy Palmer, a meteorologist at the Monterey office, said the event is a little unusual because winds would mostly blow from north to south. Such winds typically turn “offshore” and arrive from the east or northeast, blowing from land to sea.
Although several weather systems have moved through in the past few weeks with the promise of significant rain that would slow the fire season, many locations have received little to no precipitation. That includes the Sacramento Valley and the Bay Area, which can be subject to frequent offshore winds in autumn. It also includes most of the Central Coast.
“Just walking around … it is brittle out there — it is just bone dry,” Palmer said.
Where significant snow is possible
A disturbance embedded along the southward diving jet stream will cause areas of heavy snow to develop in the central and northern Rockies.
Heavy snow is predicted in many parts of southern Montana. In Bozeman, for example, at least eight to 12 inches of snow is forecast, with snowfall rates up to an inch per hour expected by Monday night. As of early Monday morning, some areas nearby had already received half a foot.
“If you must travel, keep an extra flashlight, food, and water in your vehicle in case of an emergency,” wrote the local National Weather Service office. “The winter storm has begun.”
In Billings, Mont., which saw a record high of 86 degrees a week ago, up to several inches of snow is predicted through Tuesday, although rain may mix in at times.
The storm will deposit a swath of heavy snow across Wyoming as well. Casper is under a winter storm warning, with 6 to 15 inches expected as wind gusts up to 45 mph reduce visibility. Snow levels will fall to around 7,000 feet Monday night before the storm peaks in intensity Tuesday and Tuesday night, bringing more widespread accumulations. Maximum snow amounts could reach two feet or so in the Bighorn Mountains.
Heavy snow is also anticipated in the high elevations of Utah and central and western Colorado, but just a few rain showers are expected in Denver. By Wednesday, the snow will be withdrawing into Saskatchewan, Canada.
Severe thunderstorm and flood risk
As the storm system ejects into the Plains late Tuesday and encounters the warm, unstable air out ahead of it, a threat of severe thunderstorms will develop in western Kansas and Oklahoma, including Woodward, Okla., and Dodge City, Great Bend and Hutchinson, Kan.
The Weather Service has placed this region in an enhanced or Level 3 out of 5 risk zone for severe thunderstorms, noting “a couple tornadoes” will be possible Tuesday evening and overnight. Large hail is likely with the storms, as well as flooding where storms repeatedly pass over the same areas. Nearly five inches fell from Sunday night’s storms as they passed through Kansas overnight.
A look back at Sunday night’s storms
The storm system predicted to pass from the Rockies into the Plains on Tuesday marks the second in just three days, trailing a powerful disturbance that entered the Southern Plains on Sunday night.
This initial system generated a dangerous line of thunderstorms that barreled across Oklahoma and northeast Texas. More than a dozen tornado reports were received across Oklahoma and the Southern Plains. The twisters mowed down trees and left behind pockets of structural damage, but no casualties have been reported.
On Monday, the leftovers of Sunday night’s severe weather will move toward the Great Lakes. Areas between the northern fringe of Michigan and eastern Missouri, including the greater Chicago area, are under a Level 2 out of 5 risk of severe weather drawn by the Weather Service. A lingering tornado threat will remain, particularly if any glints of sunshine can heat the ground ahead of the encroaching batch of storms.
This same storm system caused heavy snow in the high elevations of Utah over the weekend, where more than 80 runners were rescued amid “near whiteout” conditions in an ultramarathon.
Jason Samenow contributed to this report.