Multiple weather fronts will push rain and snow into the Midwest, the Southeast, the mid-Atlantic and the Northeast ahead of Thanksgiving week and some of the year's busiest travel days.
Late Sunday, more than 25 million people were covered by National Weather Service watches and warnings related to winter storm activity, including those covering winds, flooding and freezing conditions.
Rain and gusty thunderstorms were forecast for parts of the central and southern Plains on Monday, and flood watches covered 4 million people from northwest Texas through central Oklahoma, federal and NBC News forecasters said.
Severe weather for West Texas, including Abilene, Wichita Falls and Midland, was likely to bring 60 mph winds, thunderstorms and even a possible tornado, NBC News forecasters said.
Get top local stories in San Diego delivered to you every morning. Sign up for NBC San Diego's News Headlines newsletter.
The unstable weather was eventually expected to affect 7 million people in the Dallas-Fort Worth region, NBC News meteorologists said.
Rain, snow expected this week
Starting in the Pacific Northwest, a "long duration atmospheric river" was expected to bring 5 inches of rain and at least 3 inches of snow to Oregon and Northern California beginning as early as Monday, federal forecasters and academic researchers said.
U.S. & World
The Center for Western Weather and Water Extremes in San Diego developed an AR1 through AR5 system for predicting the potency of atmospheric rivers that is similar to one used for hurricanes. On Friday it said the incoming atmospheric river — with likely impacts Tuesday through Friday — was likely to arrive as an AR3- or AR4-level phenomenon, indicating strong to extreme precipitation.
The National Weather Service’s Weather Prediction Center said the stream of precipitation overhead would bring a chance of snow to parts of Colorado, Kansas, Nebraska, South Dakota and Wyoming after it exits the Pacific Northwest.
Waves of low pressure were expected to follow and spread out into the Midwest, the Southeast and the Northeast after the initial atmospheric river, drawing in colder air and producing some snow into the weekend that precedes Thanksgiving week, they said.
An upper-level low pressure system was forecast to develop above the Great Lakes and the Northeast in the latter half of this week, the National Weather Service's Weather Prediction Center said.
The system would draw down temperatures and block any prospective warm fronts, it said.
"This will result in cooler temperatures, a cold rain from the Ohio Valley to the East Coast, and early season accumulating snow for the central Appalachians and the higher terrain of the interior Northeast," the center said in its latest forecast.
Cooler, wetter fronts were expected to affect the East Coast in the second half of this week, when rain and some accumulating snow are expected in the Great Lakes, the Ohio Valley and the Northeast.
Federal forecasters said a surface cyclogenesis — a possibly major winter storm — could develop and spin across the mid-Atlantic and southern New England regions, bringing temperatures down by 10 degrees and producing rain and some snow accumulation Wednesday and Thursday.
Snow could be limited to the Northeast's interior regions and mountain ranges, federal forecasters said, but it would come amid drought and even wildfires that have so far characterized fall in places like New York, New Jersey and Pennsylvania.
Forecasters said as much as 6 inches of snow was possible.
"Cold air aloft will be sufficient to support accumulating early season snow for the higher terrain near the Great Lakes and interior Northeast, and especially for the central Appalachians," the Weather Prediction Center said in its forecast Sunday.
Looking ahead to Thanksgiving
Federal forecasters often avoid making predictions beyond seven days but were confident that cooler temperatures, cold rain and high-elevation snow would arrive on the East Coast on the Sunday of the week that marks the Thanksgiving holiday, Black Friday shopping and one of the busiest periods of the year for travel.
Nearly 80 million people are expected to travel more than 50 miles in the holiday period, the AAA said Monday, with unprecedented numbers set to drive and fly to see friends and family.
The U.S. Climate Prediction Center’s six- to 10-day weather outlook, which reaches into the first half of the holiday week, said California, the Pacific Northwest, Montana, North Dakota, South Dakota, Nebraska, Iowa, Minnesota and some Great Lakes states, such as Wisconsin and Michigan, were “leaning” in favor of above-average rain.
The outlook has the San Francisco Bay Area likely to get more rain. The rest of the country is likely to get normal precipitation or below-normal rain during that time, the prediction center said.
There are indications Thanksgiving week will continue a post-pandemic trend of increasing holiday travel. American Airlines said in a statement Thursday that it expects to set a record for passengers served during the holiday span, with nearly 8.3 million expected.
The last high mark for travelers carried by American came last year, when it estimated nearly 6.5 million people flew on its aircraft and those of subsidiary airlines.
Likewise, the National Retail Foundation said Thursday it expects a record for the number of shoppers expected to set foot in brick-and-mortar retailers during the holiday week: 183 million.
It may be too early to tell whether brewing rain and snow systems will thwart travel and spending plans.
This article first appeared on NBCNews.com. Read more from NBC News here:
