With the Thanksgiving journey well underway, many have reached their destination – but for everyone else, a storm moving from the Rockies to the Midwest and Northeast tomorrow will bring rain and snow, which is likely on flights and crowded streets.

Nearly 3 million people are expected to be screened by TSA today, and a record 71.7 million are expected to travel by car over Thanksgiving – over 1 million more than last year.

The storm, which is already dropping snow across the Rockies on Wednesday morning, is expected to move east throughout the day today and into the Midwest and Northeast through Thanksgiving.

There will be rain that will become more intense in the evening from St. Louis to Indianapolis and to Pittsburgh.

Airports in Denver, Kansas City and St. Louis are expected to see impacts from this weather today, NBC News’ Al Roker said on “TODAY” Wednesday, with slowdowns possible in Nashville, Dallas, Houston and Austin.

According to FlightAware, air traffic was relatively smooth on Wednesday morning, with nearly 500 flights delayed and 20 canceled.

A ground delay at Newark Liberty International Airport in New Jersey due to a shortage of air traffic controllers was lifted at 1 a.m. Wednesday.

For road travelers, I-80, I-64 and I-75 will be affected by rain on Wednesday and I-25 and I-70 in the Rocky Mountains will be affected by snow.

Thanksgiving Day will bring plenty of rain for the I-95 corridor from Florida to Maine and accumulating snow for the interior Northeast and northern New England.

Points north of the Hudson Valley in northern New York State and inland New England can expect 1 to 3 inches of wet snow, with local totals exceeding 6 inches on the highest mountain peaks.

The iconic Macy’s Thanksgiving Day Parade will take place rain or shine, as the Big Apple is forecast to see pouring rain with temperatures in the high 40s. Wind speeds of less than 10 miles per hour are forecast, allowing balloons to fly. The parade’s popular balloons cannot fly when maximum sustained winds reach 23 miles per hour or more or when gusts reach more than 34 miles per hour.

Cities on the East Coast, including Baltimore, Washington DC, New York, Hartford and Boston, can expect cold rain, with rainfall amounts ranging from 0.50 to 1 inch. Traffic will be smooth as far west as Virginia and Maryland, including along the I-95 corridor into Maine.

Travel conditions will largely return to normal during the overnight hours into Friday morning as the system moves out of the New England region.

However, a lake effect snow event is beginning around the Great Lakes and will last through Sunday.

Airport hubs to keep an eye on Thursday include Atlanta, Charlotte, Washington DC, 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 much of the country, as will lake-effect snow around the Great Lakes and the Northeast.

A total of 3 million people are estimated to pass through TSA on Sunday, closing in on the record of 3.01 million set the Sunday after the Fourth of July holiday this year.

Chicago and Detroit could experience some problems at their airports on Sunday, but the East and West Coasts appear to be favorable for road and air travel.

Meanwhile, much of the Northern Plains and Upper Midwest will be bitterly cold by the end of the week, with temperatures expected to be 10 to 20 degrees below average beginning on Thanksgiving Day.

Thursday through Sunday will see highs in the 30s and 20s and lows in the teens in Chicago, highs in the 40s and lows falling to around 28°F in New York, and highs in the 50s and 40s in DC -Range and lows in the 30s and high 20s. Minneapolis will see lows in the single digits over the weekend.

As travelers take to the skies to meet loved ones, authorities are warning people who park their cars in airport parking lots to be careful about vehicle theft.

This year, more than 300 cars have been stolen from the nation’s busiest airport, Hartsfield-Jackson Atlanta International Airport – nearly three times as many as last year, Atlanta police said.

“Suspects can program key fobs onto vehicles, and that’s what got us to where we are now,” said Maj. Kelley Collier, the Atlanta airport district commander. This year, police are introducing cameras, motorcycle patrols and new fences to curb crime in the 30,000 parking spaces.

More than 50 vehicles were also stolen from Dallas Fort Worth International Airport this year in what police say was a car theft ring that targeted airports in several states. DFW Airport police arrested the suspected ringleader last month.

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

“Complete disbelief that we had parked at an airport and came out and our car was gone. We just assumed it was safer in that environment,” she said. Police later found it abandoned and completely stripped.

“I hope the airports increase their security so we can travel and come back and have your car there,” she added.