With Thanksgiving holiday travel well underway, many have reached their destinations — but for everyone else, a storm tracking from the Rockies to the Midwest and Northeast into Thursday will bring rain and snow, likely impacting flights and packed roads.

Just shy of 3 million people were expected to be screened by the Transportation Security Administration on Wednesday, and a record 71.7 million were expected travel by car over Thanksgiving — over 1 million more than last year.

The storm, which dropped snow over the Rockies Wednesday morning and slowed by the afternoon, is forecast to race east throughout Wednesday to the Midwest and Northeast through Thanksgiving.

It'll bring rain, with the possibility of ice and snow, that will intensify in the evening from St. Louis to Indianapolis and into Pittsburgh.

Overnight, the storm will continue to move eastward, bringing cold rain along the I-95 corridor, from Richmond to Boston, in the early hours of Thanksgiving morning.

As of Wednesday night, there were nearly 4,000 delays and 45 cancelled flights within, into or out of the U.S., according to FlightAware.

American Airlines said it operated nearly 6,400 mainline and regional flights on Tuesday and expected more than 650,000 customers to travel Wednesday across nearly 6,400 flights — that's almost 4.5 American flights departing every minute of the day.

A ground delay at Newark Liberty International Airport in New Jersey, due to a shortage of air traffic controllers, was in place Wednesday starting at 1 p.m. ET to 2 a.m. Thursday.

There were more than 300 delays in total out of Newark on Wednesday, with some at least 95 minutes long.

The FAA said on X Wednesday afternoon that delays were expected in Denver and Salt Lake City due to snow and ice. 

In those cities, airport officials were deicing planes to get them ready for departure. Denver was leading the pack with 600 flight delays Wednesday.

Delays were also common in Boston, Dallas and Las Vegas, where delays were in the triple digits, according to FlightAware.

Fog in Tampa was affecting departures Wednesday, with Tampa International Airport reporting 37 outbound delays, according to FlightAware. Delays were also an issue in Seattle and Los Angeles, where low ceilings were expected to cause some impacts on operations, the FAA said earlier Wednesday.

For road travelers, I-80, I-64, I-75 were impacted by rain Wednesday, and I-25 and I-70 by snow in the Rockies. 

Thanksgiving Day will bring a mess of rain for the I-95 corridor from Florida to Maine, and heavy snow for the interior Northeast and New England.

Points north of the Hudson Valley in upstate New York and interior New England can expect 1 to 3 inches of wet snow, with localized totals of over 6 inches at highest mountain peaks.

From northeast Pennsylvania to New Hampshire, 3 to 6 inches of snow — and potentially even more — is possible, with windy conditions potentially leading to power outages in the area.

The iconic Macy's Thanksgiving Day Parade will go on rain or shine, as the Big Apple is forecast to see soaking rain with temperatures in the 40s. Winds are forecast to be less than 10 mph, which will allow balloons to fly. The parade's beloved balloons cannot fly if maximum sustained winds hit 23 mph or greater or if gusts exceed 34 mph.

East Coast cities including Baltimore, Washington, D.C., New York, Hartford and Boston can expect a cold rain, with rainfall totals between .50 to 1 inch. Road travel will be slick as far south as Virginia and Maryland, including through the I-95 corridor into Maine. 

By the overnight hours into Friday morning, travel will settle to mostly normal conditions as the system pushes out of the New England area.

However, cold winds in New England and a lake effect snow event around the Great Lakes will take hold and will continue through Sunday.

Airport hubs to watch Thursday include Atlanta, Charlotte, Washington, D.C., Philadelphia, NYC, Boston, Pittsburgh and Buffalo.

On Sunday — typically the busiest travel day of Thanksgiving week, as people return home from holiday trips — the cold will continue across swaths of the country, as well as lake effect snow around the Great Lakes and Northeast.

A total of 3 million people are predicted to pass through TSA on Sunday, nearing the record of 3.01 million that was set the Sunday following the Fourth of July holiday this year.

Chicago and Detroit may see some problems at their airports on Sunday, but the East and West Coast look favorable for road and air travel.

All the while, much of the northern Plains and upper Midwest will see bitter cold to close out the week, with temperatures forecast to be 10 to 20 degrees below average starting on Thanksgiving Day.

From Thursday to Sunday, Chicago will see highs in the 30s and 20s and lows in the teens, New York will see highs in the 40s and lows dip to around 28F, and D.C. will see highs in the 50s and 40s and lows in the 30s and high 20s. Minneapolis will see lows into the single digits over the weekend. 

As travelers take to the skies to join loved ones, authorities are warning people who leave their cars in airport parking lots to take caution due to vehicle thefts.

Over 300 cars were stolen from the nation's busiest airport, Hartsfield-Jackson Atlanta International, this year — nearly three times as many as last year, Atlanta police said.

"Suspects can program key fobs to vehicles and that has gotten us here where we are now," Maj. Kelley Collier, the Atlanta Airport precinct commander said. This year, police are adding cameras, motorcycle patrols, and new fencing to curb crime across its 30,000 parking spaces. 

More than 50 vehicles were also stolen from Dallas Fort Worth International Airport this year, as police said a car theft ring targeting airports across multiple states was responsible. DFW Airport Police arrested the alleged ringleader last month.

A woman named Katy told NBC News that she and her husband went on a work trip and returned to Columbus International Airport to find their car was gone.

"In complete disbelief that we had parked attached to an airport and came out and our car was gone. We just assumed it was more safe and secure in that type of an environment," she said. Police later found it abandoned and completely stripped. 

"I'm hoping that the airports will beef up their security so that we can travel and come back and have your car there," she added.