Powerful winter storm roils travel across the US, wreaking havoc for flights and public transit

NEW YORK — A powerful winter storm is roiling travel across the northeastern U.S.

Heavy snow, strong winds and blizzard warnings have prompted transportation shutdowns, forcing millions of people to stay home. Air traffic is also coming to a standstill in much of the much of the region, with thousands of flight cancellations piling up across major hubs like New York and Boston. And trains have suspended some of their service.

The National Weather Service on Monday called travel conditions ''extremely treacherous'' and ''nearly impossible'' in areas hit hardest by the storm.

Here's what we know.

Flight cancellations pile up

Thousands of flight disruptions piled up Monday morning. As of around 12:30 p.m. ET, more than 5,600 flights in or out of the U.S. were canceled, according to online tracker FlightAware. Hundreds of others were delayed.

New York's John F. Kennedy International Airport and LaGuardia Airport had the highest numbers of cancellations Monday — followed by airports in Boston, Newark, New Jersey, Philadelphia and Washington, D.C. Rhode Island's T.F. Green International Airport also announced Monday that it was temporarily suspending all of its airport operations.

The Federal Aviation Administration urged travelers to monitor updates and check with airlines and airports on the status of their flights.

U.S. airlines are required to provide refunds for flight cancellations. Or, when airlines expect bad weather to create problems for flights, they often give travelers a chance to postpone their trips by a few days without having to pay a fee. Carriers like JetBlue, Delta, Southwest and American are already offering options for select impacted customers to rebook their trips at no cost.

Air travelers aren't only seeing winter weather disruptions this week. As part of a partial government shutdown, the Department of Homeland Security suspended its Global Entry program over the weekend, which typically allows pre-approved travelers to use expedited kiosks when entering the U.S. from abroad. The department had previously planned to halt the Transportation Security Administration's PreCheck program as well, but canceled that closure.

And after the Mexican army killed Jalisco New Generation Cartel leader Nemesio Oseguera Cervantes on Sunday, several airlines canceled flights or issued other travel advisories for airports in cites like Puerto Vallarta and Guadalajara, where government officials are also urging residents to stay inside their homes.

Travel bans on roads and public transit disruptions

Millions of people under blizzard warnings are facing bans on non-emergency travel. On Sunday night, cellphones across New York City received wailing push alerts announcing a ban on non-emergency travel on all streets through noon Monday, due to ''dangerous blizzard conditions.'' Rhode Island and New Jersey implemented similar restrictions.

Public transit ground to a halt in some areas, or saw significant disruptions.

As of midday Monday, New York's Metropolitan Transportation Authority said that it had ''removed articulated buses from service during the storm'' and that there may be delays on the subway, especially for routes running outdoors. The Long Island Rail Road also temporarily suspended all services until further notice.

In Boston, the Massachusetts Bay Transportation Authority also reduced service for its subway, bus and commuter rails.

Havoc for train routes

Amtrak announced that it would be suspending all service between New York Moynihan Train Hall and Boston South Station until at least 4 p.m. ET on Monday. Other routes also saw disruptions. Amtrak said impacted customers would be notified directly and have the chance to rebook or request refunds.