(CNN/WSVN) — There appears to be no end of trouble in sight for flyers this week — a chaotic July Fourth weekend has spawned at least 1,100 cancellations since Friday as airlines grapple with staffing shortages and poor weather amid an abundance of passengers.

More than 7,800 US flights were delayed Friday — including 45% of JetBlue’s operations and almost a third of United, American Airlines and Southwest’s operations. Delta also saw a quarter of its operations delayed.

Thunderstorms in the Northeast Friday afternoon were to blame for causing delays of an hour or more at some of the region’s major airports, according to the Federal Aviation Administration’s flight delay map.

Delays have eased up, however, with about 4,900 flights delayed in the United States and 644 cancellations as of Saturday evening. Delays were concentrated in New York-area airports, according to FlightAware data.

Even with the high number of travelers, 7News cameras captured lines moving smoothly at Miami International Airport, Saturday afternoon.

“I think people are in good spirits. I haven’t seen any people frustrated or mad or anything,” said traveler Aaron Bennett.

There were lots of “on time” notices for American Airlines at its major hub of Miami, despite a computer glitch that allowed 12,000 pilots to drop their flights.

CNN has reached out to airlines for comment.

United Airlines has waived change fees for travelers affected by Northeast thunderstorms and severe weather in Denver and Houston.

Saturday night, a spokesperson for American Airlines addressed the computer glitch. It read in part, “We already have restored the vast majority of the affected trips and do not anticipate any operational impact because of this issue.”

Airlines were bracing for holiday weekend crowds at levels not seen since before the pandemic. Delta offered customers free flight changes with no fee difference for those traveling between July 1 and 4.

So far this year, US airlines have canceled 3.5% of flights, up 42% over 2019, according to Department of Transportation data.

The TSA said it screened 2,490,490 passengers on Friday, more than the number of passengers screened on that day in 2019, when 2,184,253 flew during the pre-pandemic holiday.

Washington is stepping up the pressure. Transportation secretary Pete Buttigieg tweeted July 1 he is “engaging airlines daily to make sure they are ready,” and reminded customers they are entitled to cash refunds for canceled flights — a rule requirement he “will continue to enforce.”

Bernie Sanders said that he wants the DoT to fine airlines up to $27,500 per passenger for delays.

“The airline industry got $50 billion in taxpayer money in its time of need,” he tweeted Friday. “What did Americans get in return? Disruptions, delays, and cancellations.”

As airlines contend with staffing shortages, Delta, United Airlines, JetBlue and Alaska Airlines have already preemptively trimmed their summer schedules.

“US airlines always strive to provide a seamless travel experience and are making every effort — including trimming schedules — to help ensure smooth travel,” Airlines for America (A4A), an industry group representing major US air carriers, said in a statement after a call with the FAA Thursday to make plans for any weather disruptions over the long weekend.

Off-duty Delta pilots, represented by the Air Line Pilots Association, picketed at the carrier’s hubs on Thursday to protest the slow progress of contract negotiations. They’re demanding improvements in pay, retirement and job protections — as well as changes to pilot schedules to avoid disruptions caused by “preventable management missteps.”

“When delays or cancellations happen, the pilots share in our passengers’ frustration. As long-term stakeholders in our airline, seeing our operational reliability suffer is bad business and puts the Delta brand at risk,” said Capt. Jason Ambrosi, chair of the Delta ALPA Master Executive Council in a release.

Airport officials advise travelers to arrive three hours early to ensure an on-time departure.

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