DALLAS — Airlines are shifting the timing of thousands of flights, even adding dozens of redeyes, as they try to avoid delays while hauling millions of passengers from now through the Christmas weekend.

Success or failure could all depend on the weather and Mother Nature isn’t making it easy on airlines.

Rain and fog in the Northeast caused delays and cancellations Wednesday in Boston, New York and Washington — the busiest part of the country’s airspace. Rain in Chicago and Atlanta caused some delays in those cities too. Severe storms that ripped through Mississippi and Alabama, however, had little impact on air travel since no major airports are in those states.

Weather wasn’t the only culprit for travel headaches. A Black Lives Matter protest in Minneapolis had clogged roads around the airport and temporarily blocked access to one of the two terminals. Passengers were moving through security again as of 4:30 local time.

There were about 5,300 delays and 430 cancelations around 8:15 p.m., according to flight tracking site FlightAware.