Millions to hit the roads for Thanksgiving ahead of 'Arctic' temperatures Thursday

Dozens of flights were canceled and thousands were delayed as millions of travelers began their journeys to reach loved ones for what forecasters predict will be a cold Thanksgiving.

The National Weather Service said that a pair of weather systems were expected to bring an "Arctic outbreak" across the Central United States into Thanksgiving.

"A significant arctic outbreak will arrive in the northern Plains on Thanksgiving and advance farther south and east on Friday into the weekend," the weather service said in its national forecast discussion on Tuesday.

Congested highways will mean ground travel will also be difficult during the lead-up to the holiday, and while there haven't been reports of widespread disruptions so far, air travelers in particular may face serious problems.

At Newark Liberty International, the Federal Aviation Administration issued a ground delay through early Wednesday over a shortage of air traffic controllers. A ground delay at Boston Logan International Airport over visibility expired Tuesday night. And ground stops were possible at busy San Francisco Airport amid lower visibility caused by fog and lingering rain, the administration and the weather service said.

At Las Vegas' Harry Reid International Airport on Tuesday, unscheduled private aircraft were prohibited from flight amid high demand for air travel, according to the FAA.

Freezing holiday weather

Temperatures in the northern Great Plains will only reach the high teens and 20s Tuesday and Wednesday, 15-25 degrees lower than the seasonal average. The weather service office for the Twin Cities said that Thursday could see lows of zero to 13 degrees Fahrenheit.

In central and southern California, the Great Basin and the Rockies, an atmospheric river event — an airborne flow of moisture that can bring heavy precipitation — was set to bring rain, as well as up to 3 feet of snow, in the southern Sierra Nevada.

It will be a wintry Thanksgiving for parts of the Upper Michigan Peninsular and areas downwind of Lake Ontario, with between 4 and 8 inches of snow expected.

Those hoping to attend the Macy's Thanksgiving Day Parade in New York City may want to pack their umbrellas as rainfall is expected Thursday, the National Oceanic and Atmospheric Administration (NOAA) said.

Black Friday shoppers won't be spared, either. Temperatures are expected to plunge 15 to 25 degrees below average from the Plains to the Great Lakes region.

"Wind chills will make it feel below zero in the northern Plains and Midwest, and lake effect snow is likely from the upper peninsula of Michigan to western New York," the NOAA said Tuesday.

Weather could affect travel plans

The National Oceanic and Atmospheric Administration warned that the "cornucopia of hazards," including snow, rain and harsh winds, may impact travel for those in the Northeast, West and Great Plains this year.

On Wednesday, storms will move east across the Rockies and bring rain and snow, with airport delays likely in Denver, Kansas City and St. Louis, NBC News’ Al Roker said on the “TODAY” show. Air delays could also hit Dallas, Austin, Houston, Detroit, Chicago, Nashville, Minneapolis and Atlanta, he said.

On the roads, interstates 55, 64, 65, 75 and 80 could all be affected Wednesday. And on Thanksgiving Day itself, the storm will strengthen as it reaches the East Coast and bring heavy rain and snow, making driving difficult along I-95 and several other major routes in the region.

"Our travel weather is going to be a real mess, you're just going to have to pack your patience, take your time, you're going to get to where you're going — it just might not be when you expect to get there," Roker said.

As of 11 p.m. ET Tuesday, 78 flights into, within and departing from the U.S. had been canceled, and more than 4,100 had been delayed, according to FlightAware flight-tracking data.

Travel hubs also seemed to cope with an uptick in passengers Monday. “I grew up in Connecticut, so I’ve been through this airport thousands of times and I’ve never seen it this easy getting through customs — no line today,” the Rev. Jeff Couture, a Catholic priest who had just returned from a pilgrimage to Portugal, told NBC New York on Monday.

Janis and Ken Allen were flying to San Francisco from Newark on Monday to visit their daughter — having traveled by train from Philadelphia due to the lack of direct flights from there — and had not experienced any delays. They told NBC New York that they planned their return journey Dec. 3 to avoid the post-holiday crush, as consumer travel groups including the AAA have advised.

This article was originally published on NBCNews.com