According to FlightAware, more than 2,600 U.S. and 4,100 worldwide flights were grounded Monday midday according to tracking service FlightAware. Additional 8,500 flights were also delayed, with 3,100 of them in the U.S.

An improving weather forecast could offer travelers some hope. Airlines cancelled fewer than 300 flights from the United States scheduled for Tuesday.

They had to first deal with a winter storm that was forecast to bring up to 10 inches (25 cms) of snow to the District of Columbia, northern Virginia, and central Maryland from Monday afternoon.

Holiday travelers who were trying to return home from vacation added more despair to their suffering with the cancellations and delays.

“It was absolute chaos,” Natasha Enos said. She spent an interminable Saturday night and Sunday morning at Denver International Airport, during what was supposed be a brief layover on a cross country trip from Washington to San Francisco.

Enos, who had booked Frontier Airlines, didn’t find out that her connecting flight to California was cancelled until she had already arrived in Denver. Enos rushed to find alternate flights and navigate through baggage-claim, which was jammed with confused and stranded travelers during the new wave COVID-19.

The 28-year old financial analyst said that there were a lot of people in small spaces and that not everyone was hiding. “There were many exhausted children and some families so stressed out.”

The spread of the highly transmissible variant of omicron has seen the average daily case of COVID-19 in the U.S. increase by three times over the past week, reaching 400,000 on Sunday according to Johns Hopkins University figures.

The number of flights that were grounded in the United States was low in the weeks before Christmas. It soared to over 1,000 per day after the virus hit, and airlines blamed the shortages on the virus.

Although airlines and passengers enjoyed mostly good weather for several days, cancellations spiked to new heights on Saturday due to a winter storm in the Midwest.

According to FlightAware, approximately 5,400 U.S. flight cancellations occurred over the weekend — almost 12% of all scheduled flights, and more than 9,900 worldwide. Many cancellations were made several hours or days in advance. Airline believes they are more likely to maintain lighter schedules in the face of disruptions like snow and thunderstorms.

Southwest Airlines had cancelled 575 flights (or 15%) of Monday’s schedule by midday. According to Brad Hawkins, Southwest Airlines’ spokesperson, storms that occurred over the weekend and Monday disrupted operations at several of its largest airports including Baltimore, Denver, and Chicago. This caused crews and planes to be out of their positions.

Delta Air Lines provided a waiver for customers to cancel flights to or from Washington and Baltimore.

SkyWest, a regional airline that operates under the names American Eagle and Delta Connection, grounded more than 300 flights Monday, after cleaning 500 on Sunday.

The authority responsible for Detroit International Airport in Michigan stated that crews are working round the clock to clear snow and maintain the airport. Atlanta’s airport authority advised passengers to arrive earlier than usual due to high passenger volumes, weather issues and staff shortages caused by pandemics. This could increase the time to clear security.

Hawaiian Airlines, which is thousands of miles away from snow storms, announced that it had to cancel many flights between the islands and across the Pacific because of staff shortages.

Temporary bonuses are being offered by airlines to pilots and flight attendants in order to help them pick up empty flights from co-workers who have COVID-19. United will pay pilots three times their normal wages to pick up empty flights during January. Spirit Airlines and the union reached an agreement to pay flight attendants twice through Tuesday.