For those already familiar with this topic, this web site contains some of the results of Chris Bailey's M.S. thesis at NC State University. In collaboration with Gail Hartfield, Scott Sharp, Kermit Keeter, Doug Schneider, and other National Weather Service personnel, Chris Bailey and Gary Lackmann at NCSU developed a cold-air damming detection algorithm.

Using the algorithm, we have identified nearly 400 potential CAD events from 1985-present. To stratify this sample within the context of the CAD sub-types identified by Hartfield et al. at NWSFO RAH and GSP, we have developed a CAD ranking system that weights several different measures of CAD intensity and duration, and ranks each event according to strength. In doing this, we find that the strongest events correspond to "classical" CAD, weaker events are often "hybrid", and some of the weak events are "in-situ". We have expanded the list of sub-types to include other variations, such as "weak onset" and "southern onset" (damming events where the parent high is too weak or too far south for a "classical" label, and no precipitation is present to allow for diabatic contribution to the cold dome, precluding a "hybrid" label).

Another surprise is the large number of weak, warm-season CAD events that have been detected by the algorithm. The warm-season events will be treated separately; the composites below are exclusively for the cold-season CAD events.

Chris utilized coarse NCEP Reanalysis gridded data to construct composites of the synoptic-scale patterns accompanying the different CAD sub-types. The results are very encouraging. Statistically, the differences between the sub-types are significant at the 99% level (as determined from a 2-sided student-t test), and clear signatures emerge for each.

Some of the sub-types are short-lived (e.g., in-situ), and so some of the composite evolution included here is meaningless. Eventually, we will refine the composite loops to be more focused on the meaningful part of the evolution, but for now, you can use the editing capabilities at the bottom of each CAD animation to exclude frames as you see fit.

Thanks for your interest... as always, comments welcome!

Gary Lackmann