Summer: delays
June-August has the highest delay rates (22-25% of flights). Thunderstorms are the main culprit, especially afternoon convective weather in the Southeast and Midwest. The airports most affected: ATL, ORD, DFW, CLT, IAH.
Winter: cancellations
December-February has moderate delay rates but the highest cancellation rates. Winter storms can completely shut down airports. Northeast hubs (JFK, EWR, BOS) and Midwest (ORD, DTW, MSP) are most vulnerable.
The best seasons
September-October and April-May are the sweet spots. Mild weather, lower passenger volumes, and fewer disruptions. If you have flexibility in your travel dates, target these months.