JetBlue and Delta are waiving fare differences on eligible flights affected by Northeast weather through Friday, Nov. 13. Both waivers cover JFK, LaGuardia, Newark and Westchester County. JetBlue adds Long Island MacArthur Airport in Islip. Delta adds Boston Logan.

If you’re flying Friday and want to change your JetBlue trip, use Manage Trips before your originally scheduled departure. The two airlines have different deadlines for taking the replacement flight.

JetBlue gives travelers through Nov. 18

The waiver covers JetBlue-operated flights to or from the five listed airports that were scheduled for Nov. 12 or 13. You can rebook for travel through Wednesday, Nov. 18, with change fees, cancellation fees and fare differences waived for eligible tickets. JetBlue’s customer notice says the original booking must have been made before Nov. 12. Its travel agent bulletin lists an earlier cutoff, so confirm eligibility with JetBlue or your agent if you booked Nov. 11.

Delta gives travelers through Nov. 16

Delta’s waiver covers travel to, from or through its five listed airports on Nov. 12 or 13, for tickets issued by Nov. 12. Both the change and the new departure must be by Monday, Nov. 16. Keep the same cabin and check the price before confirming. Delta says a fare difference can apply if the waiver requires the original booking class and that class is unavailable, or if you change the origin or destination.

The U.S. Department of Transportation says you’re entitled to a refund when the airline cancels or significantly changes your flight and you decline the alternatives it offers. Check the airline’s flight status before making a voluntary change.