The snowstorm expected late Thursday will impact travel to, from, and through the Northeast.

US Airways Group, Southwest Airlines, and Delta Air Lines issued winter weather advisories.

US Airways, the dominant airline at Philadelphia International Airport, is waiving change fees for travel through Jan. 8, and will extend the time limit if necessary, said airline spokesman Todd Lehmacher.

Southwest, which does not charge change fees, said it is monitoring the storm as it moves through the Midwest to the Northeast, and warned travelers that scheduled flights may be delayed, diverted, or canceled.

Southwest said passengers with reservations to and from 17 cities, including Philadelphia, can reschedule their flight within 14 days of their original travel date.

US Airways canceled three flights to Boston after 7:15 p.m. and a 10 p.m. flight Thursday to New York LaGuardia airport.

US Airways canceled the last departing flights Thursday to Newark, N.J., White Plains and Islip, N.Y., State College, Pa. and New Haven, Conn., Lehmacher said.

"We've decided to not put in the overnight flights to places like Boston, Mass., Albany, N.Y., Providence, R.I., Manchester, N.H., and Hartford, Conn.," Lehmacher said.

Travelers can go to usairways.com and change the flight themselves.

Major airports in the Northeast and Midwest were hit with flight cancellations, according to the flight-tracking company, FlightView Inc.

As of 1:30 p.m. Thursday, 691 flights were canceled in and out of Chicago O'Hare; 397 flights canceled at Newark Liberty International, and 244 flights canceled at Cleveland's Hopkins International airport.

Boston had 210 flight cancellations and New York LaGuardia airport reported 219 canceled flights. Philadelphia International had 96 canceled flights, according to FlightView.

The Federal Aviation Administration website showed air traffic was being delayed at departure cities Thursday into Chicago O'Hare and Midway, and Detroit Metropolitan airports.

Delta issued a winter weather advisory for eight states: New Jersey, Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island and Vermont.

Delta said passengers in the affected states can edit their itinerary at delta.com for travel on or before Jan. 8 and change fees will not apply.

Amtrak said it will operate a modified snow schedule Friday due to the winter storm forecast expected to impact the Northeast.

Passengers using Acela Express and Northeast Regional service between Boston and Washington should expect reduced frequencies, particularly in New England.

Corridor services, including the Keystone Service (New York to Harrisburg), Empire Service (between New York City and Albany), Amtrak Downeaster (Brunswick, Me, to Boston), and most of the Springfield Shuttle (between New Haven, Ct. and Springfield, Mass.), are expected to operate a normal schedule.

Amtrak said passengers holding reservations that require modification are being notified by Amtrak customer service and accommodated on other trains.

A range of tools - including Amtrak.com, smartphone apps and 1-800-USA-RAIL - are available to assist in travel planning.

Passengers who have paid, but choose not to travel due to this service disruption can receive a refund or a voucher for future travel.

Some reservations booked online can be modified or canceled on Amtrak.com or by using the free Amtrak mobile app. Passengers are encouraged to call 800-USA-RAIL or visit Amtrak.com/alerts for Service Alerts and Passenger Notices. Schedule information and train status updates are available on the Amtrak.com home page.

lloyd@phillynews.com

215-854-2831