And they’re off!

Tens of millions of Americans are on the move for the annual November trek to see family and friends, feast on turkey and pumpkin pie, and rediscover the joys of their hometown on Thanksgiving.

You probably know the drill: packed airports, crowded flights and lots of out-of-state license plates on the road.

All eyes are on the weather, which can turn a simple trip into a nightmare — cue visions of Steve Martin and John Candy struggling to get to snowy Chicago in “Planes, Trains and Automobiles.”

On Tuesday, travelers are facing stormy conditions in the Pacific Northwest, the threat of floods and severe storms in the South, lots of rain in the Northeast and the possibility of snow in parts of New England.

But that’s not keeping people home.

AAA projects that 42.5 million Americans will travel at least 50 miles during the Thanksgiving weekend, an increase of 4% from last year.

Slightly fewer people are choosing to get to their destinations by plane.

About 23.2 million travelers will fly over a 12-day period surrounding Turkey Day, a 2% drop from last year, according to a forecast by the Air Transport Association of America.

Unlike last year, when the “National Opt-Out Day” movement against airport body scanners threatened to snarl security lines across the country, air travelers are not facing the prospect of protest-induced delays. (The Opt-Out Day turned out to be a non-event.)

The TSA says it’s preparing its work force for a “smooth holiday travel experience for travelers.”

The busiest air travel days for the Thanksgiving holiday period are expected to be Sunday, November 27, and Monday, November 28, the Air Transport Association of America said.

If you’re flying into or out of Los Angeles International, Chicago’s O’Hare International or Orlando International, brace yourself for lots of company. Those will be the nation’s busiest airports this Thanksgiving, based on flight bookings, according to Orbitz.com.

(And in case you’re wondering, Mineta San Jose International in California and Kahului Airport in Maui, Hawaii, will be the least busy.)

No matter where you start your journey, flight attendants say, it’s a week when they see lots of extra-grumpy passengers worried about flight delays and cancellations.

“There’s a little bit more at stake. Oftentimes, people are trying to get someplace to be with their family, so naturally they would be upset if they’re not going to make it,” said Rene Foss, a veteran flight attendant for a major U.S. airline.

“However, in general, it’s also kind of a festive time. Sometimes, contrary to what you might think, people are in a good mood because they are going for something kind of fun as opposed to just a business meeting or something related to work.”

Flying with food or gifts? Check out the TSA’s guide to what you can and cannot bring through an airport security checkpoint. The agency reminds you not to wrap gifts you are taking on the plane because security officers may have to unwrap them if they need to take a closer look.

The TSA also offers tips on how to get through the security line faster, including packing coats and jackets in checked bags whenever possible and putting your shoes directly on the conveyor belt instead of a bin when they go through the X-ray machine.

Then, there are things you can’t control: Snow, fog or rain may mean you won’t fly on time or at all.

To avoid being stuck at the airport, sign up for airline alerts and check your flights frequently online before you leave home. If your flight is canceled, get in line for assistance and try your airline by phone or online at the same time to get an edge over other fliers who are trying to rebook.

If you’re driving through an area that’s expecting wintry weather, AAA recommends that you keep at least half a tank of gas in your car at all times and pack a cell phone, plus blankets, gloves, hats, food, water and any needed medication in case you’re stranded.

Stay safe out there, and happy travels.