Monday's severe weather in the Northeast led to nightmare flight delays nationwide

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Planes remain at the terminal at Ronald Reagan Washington National Airport in Arlington, Virginia, on July 8, 2019, after a storm delayed flights.

• More than 8,700 flights were cancelled or delayed in the US on Monday during a day of severe weather.
• While the worst of the delays were in the Northeast, where there was torrential rain and thunderstorms, delays reverberated around the country.
• Flash flooding also snarled New York City's subway system, causing some stations and tunnels to fill with water. 
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Severe weather in the Northeast on Monday led to a nightmare day of air travel throughout the country.

Torrential rains and flash flooding, combined with a daylong threat of thunderstorms and the tail-end of this weekend's heatwave led to more than 7,500 delayed flights going into or out of US airports yesterday, and more than 1,200 cancellations, according to data from FlightStats.

That included around 1,000 delays and cancellations at Newark, nearly 800 at La Guardia, and more than 500 in Philadelphia.

Although the worst of the weather and delays were in the Northeast, the issue compounded and affected flights around the country as aircraft arrived late at destinations, adding delays throughout the day. 

Business Insider retail reporter Áine Cain was on her way to New York from Anchorage, Alaska, on a United Airlines flight Monday evening but was unable to get home. The airline routed her through Houston, but when that flight became delayed multiple times, she was forced to rebook on a different airline, delaying her total travel time by roughly 36 hours.

Áine Cain / Business Insider

Delays and cancellations piled up, she said, leading to long lines and frustrated customers at the airport.

"Customer service was a nightmare," she said. "Airline employees working at Anchorage could have eased a lot of the stress by just being honest and giving clear instructions. The line was moving at a glacial pace, and no one was sharing clear information."

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Frustrated flyers vented their frustrations on social media as the delays and cancellations piled up.

"Still in disbelief at yesterday's fiasco," one user tweeted this morning. "Cancelled flights ALL DAY and NIGHT."

"Help pls. All my flights getting cancelled," tweeted another user with a photo of a flight board showing cancellations to New York-area airports.

While operations were smoother by Tuesday morning, a line of thunderstorms was still causing inbound and outbound delays at Newark, La Guardia, and Boston's Logan airport.

Áine Cain contributed reporting to this story.