July was hit hardest by extreme weather last year, with 7,996 delays, according to federal data. It was the worst month for those delays dating back to at least 2016. July was the worst month of the year by that metric in six of the past eight years.

Between June and August of last year, there were nearly 20,000 delays due to extreme weather. That’s more than the number of those delays in the six least-affected months combined.

Why delays are worst in the summer

The Department of Transportation defines extreme weather delays as those caused by actual or forecast “significant meteorological conditions” such as a tornado, blizzard or hurricane that would delay or prevent the operation of a flight.

Delays caused by non-extreme weather are lumped into another category that also includes airport operations, heavy traffic volume and air traffic control. Transportation Department statistics show that weather accounts for the highest share of those delays — often more than 60 percent — in the months between May and August.

Summer thunderstorms include “lightning that can stop airport operations, in some cases completely shutting down arrivals and departures at major airports,” Robert W. Mann, a consultant and former airline executive, said in an email. The bad weather can halt traffic along busy flight corridors. He said those summer conditions are more likely and widespread than winter disruptions, making delays in the summer more prevalent.

Kathleen Bangs, spokeswoman for the flight-tracking service FlightAware and a former airline pilot, said lines of thunderstorms rolling in can force an airport to quickly adjust operations, including the direction planes take off and land.

“That doesn’t tend to happen in the winter,” she said. “You don’t have so many rapid changes in such a short period of time.”

Few protections for weather delays

For summer travelers, the collision of storm delays and full flights can lead to extra frustration. Mann pointed out that there would probably be fewer empty seats to accommodate passengers whose flights were canceled or who missed connections.

“With so many people traveling in summer, your options can be quite limited,” said Katy Nastro, spokeswoman for the cheap-flight alert service Going.

Also limited: the responsibilities of airlines when delays are caused by weather. Major carriers have committed to taking certain actions for customers like offering meal vouchers and hotel stays in the case of cancellations and long delays that are caused by “controllable” circumstances.

“Unfortunately, that uncontrollable scenario gives you the least amount of rights,” Nastro said.

Still, regardless of the reason, if a flight is canceled or delayed significantly and a passenger ends up not traveling, they have the right to a refund. Once a new DOT rule goes into effect later this year, those refunds must be issued automatically.

How to avoid flight delays

Air travel experts say passengers should keep some tips in mind for the best chance at smooth sailing during stormy months.

Nastro said that if people are still planning their travel — or have the ability to change an existing trip — they should take the earliest flight of the day they can find. The chance of bad weather is lower, and planes are usually waiting at the airport, so the risks of delay are limited. And if something were to go wrong, travelers would still have time to try to catch later flights.

Another benefit to morning flights? “You’ll almost always get a smoother ride,” Bangs said.

Travelers should also take nonstop flights whenever possible to avoid the chance of disruptions during layovers and potentially missing connecting flights.

Bangs recommends checking the National Weather Service’s national forecast chart and a Federal Aviation Administration page that shows the status of the country’s airspace. If there are big storms or delays where you’re going, it might give you a chance to make alternate arrangements proactively.

“It gives you that information so you can kind of start seeing ahead,” she said. “I look at the country as kind of a big chess board and you can get ahead a few moves by knowing what’s going on.”

If you know before heading to the airport that your flight will be delayed, experts suggest playing it safe and still showing up on schedule as long as the posted delay is two hours or less. If you do want to linger at home, use a flight-tracking site like FlightAware or Flightradar24 to track your plane’s location and make sure you’ve signed up for airline notifications.

“Be very careful about what you choose to do,” travel analyst Henry Harteveldt, president of Atmosphere Research Group, told The Washington Post last year. “Ultimately, the airline is not responsible for making sure you’re on the plane. That’s up to you. When departure time comes, that plane is going to leave.”

Andrea Sachs contributed to this report