Midway Airport finished dead last both for on-time arrivals and departures among major American airports for December 2013 — with O’Hare International Airport also near the bottom in both categories, according to just-released U.S. Department of Transportation statistics.

O’Hare’s on-time performance dropped for the second month in a row, even though a new runway pattern was supposed to reduce delays in all weather conditions.

Chicago Department of Aviation spokesperson Karen Pride said weather was a factor in overall delays at both airports, with snow affecting airport operations 17 out of 31 days in December. She also pointed to airline operational performance — such as mechanical or crew issues — to explain delays and noted that the new O’Hare runway has increased the number of arrivals the airport can handle in one hour.

Things were so bad at Midway in December, 2013 that only about 41 percent of flights left on time — compared with 64 percent in the same month a year earlier, according to the data. Even at Baltimore-Washington International Thurgood Marshall Airport, which came in second to last in the latest data, 57 percent of flights left on time. It was only slightly better at O’Hare, where about 58 percent of flights departed on time in the last month of 2013, compared with about 72 percent in December 2012.

For those flying to Midway in December 2013, about 59 percent of those flights were on time, compared with 78 percent for the same month the previous year. At O’Hare, 62 percent of arriving flights were on time in December 2013, compared with about 75 percent in 2012.

Weather was likely a major factor last year. In all of December, 14.2 inches of snow fell, compared with 0.9 inches for the same month in 2012, according to the National Weather Service.

Miami International Airport came in first both for on-time departures — 78 percent — in December 2013 and arrivals — also 78 percent.

In other findings, five of the nine longest delays on the tarmac occurred at O’Hare Dec. 8. In the worst case, passengers traveling on a United Airlines flight to Paris waited on the tarmac for 4 1/2 hours before takeoff. A snowstorm, which dropped 3.1 inches at O’Hare on that day, led to the delays, officials said.

Contributing: Mitch Dudek