Blizzard has led to nearly 7,000 canceled flights

Airlines have canceled nearly 7,000 flights so far this weekend and are starting to cut service on Monday, as driving snow and ice bring many East Coast airports to a standstill.

The bulk of Saturday's 4,459 cancelations are at airports in the New York City and Washington metro areas, according to flight tracking service FlightAware. Another 2,467 flights were canceled for Sunday, and the count keeps rising.

As the storm intensified, United Airlines announced it would not operate out of Washington D.C. airports on Sunday. It says it expects to gradually resume service on Monday. At New York City area airports, it expects "very limited" service starting Sunday afternoon.

The number of cancelations for all airlines on Monday is 320, but FlightAware says that is sure to rise.

The tally since Friday of cancelled flights now tops 10,000. Cancelations have centered on Charlotte and Raleigh, North Carolina, Philadelphia, Washington and New York, with airlines essentially shutting down all flights into those cities.

One bit of good news: Saturday is the slowest travel day of the week. There were a little more than 22,000 flights scheduled to, from or within the U.S., according to FlightAware. That's about 5,000 fewer flights - and 400,000 fewer passengers - than Thursday or Friday.

Amtrak has also canceled or cut back on service. Several trains scheduled to depart Washington D.C. for New York City were canceled. There is also no service from Washington to stations in Virginia and the Southeast, according to Amtrak's website.

All major airlines have issued waivers for travel over the weekend, allowing passengers to rebook onto earlier or later flights to avoid the storms. The airports included vary by airline but include some cities in Kentucky, Tennessee and West Virginia all the way up the coast to New Hampshire and Massachusetts. As of late Friday night, American Airlines alone has issued waivers for 42 airports.

Passengers looking to cancel trips should wait until the airline officially calls off the flight. Airlines have been much more proactive in recent years about canceling flights, often doing so up to a day in advance. More travelers are impacted, but they aren't stuck waiting in airports. It also lets airlines restart the system quicker because they have planes and crews in place.