This document analyzed spatial and temporal patterns of flight delays in the US during 2012. Statistically significant clustering was found for certain delay types in different regions and seasons. Extreme weather delays clustered in the southern Great Plains in spring/summer, while NAS (National Aviation System) delays clustered in the Rocky Mountains and Minnesota/Michigan in winter and Florida/East Coast in summer. Aircraf arriving late delays clustered along the entire west coast year-round. The objective was to understand regional and seasonal patterns in delay types related to weather conditions.