On the eve of Independence Day, there is travel chaos at US airports, and more than 100 million Americans are under severe weather warnings.
While a stifling heatwave continues in the country's south and west, millions of residents in the east face serious storm threats.
The Transportation Security Administration screened the most air travelers ever on Sunday.
But through Monday morning, over a thousand flights had been rescheduled or canceled.
According to information from the FlightAware website, United Airlines continued to be the most severely affected, accounting for over 100 such incidents.
Over the past week, the major carrier has experienced more delays and cancellations than any other US airline combined, by a considerable margin.
In order to avoid being hindered by the airline's delays, CEO Scott Kirby took a private flight from New York to Colorado on Friday, for which he was compelled to apologize.
In a letter to staff members on Saturday, he claimed that thunderstorms at United's busiest hub in New Jersey had resulted in "one of the most operationally challenging weeks I've ever experienced.".
A family from Atlanta who spent five days stuck in three different airports complained that the airline's offer of 30,000 frequent flyer miles was not much of an apology.
Industry representatives were worried that a new 5G rollout near airports might interfere with aircraft technology before the long Fourth of July weekend.
However, a spokesperson for the Transportation Department told CBS News that no significant flight delays were caused by the situation.
In response to a number of recent aviation-related problems, Secretary of Transportation Pete Buttigieg stated on Sunday that more was being done "to ensure that there is the smoothest possible experience for air passengers everywhere.".
Although bad weather will still "put enormous pressure on the system," the Federal Aviation Administration will hire 1,500 new air traffic controllers this year and another 1,800 the following year.
On Monday, thunderstorms, some of which will produce large hail, are expected across the eastern United States, from Mississippi to Massachusetts, as well as in states further north, like Minnesota and Montana.
The heatwave will continue to affect the US south, and record-breaking temperatures are predicted to move up the west coast into California and even Oregon.
After storms tore through the Midwest over the weekend, more than 180,000 people still don't have electricity.
That includes more than 50,000 people in Missouri, where hailstones were thrown at homes and trees were uprooted by strong winds in some areas of the state.