Patterns of thickness anomaly for explosive cyclogenesis over the west-central North Atlantic Ocean

Composite patterns for the 26 strongest cases of cyclogenesis differed markedly from those for the 22 weakest. After a filtering to remove the shortest waves, those for the strongest developments showed a prominant negative anomaly area of large scale, centered over western Canada 5 days before the event, moving southeastward to the western Atlantic days after cyclogenesis. No such pervasive anomaly patterns was seen for the weakest cases. The most intense cyclogenesis occurred when the air over the region of development was slightly colder than the 15-yr average, while the least intense occurred in slightly anomalous warmth. In the zonal average from 25° to 125°W, the strongest cases occurred with warmth in polar latitudes, coldness in middle latitudes and anomalously strong westerly thermal wind in the cyclogenetic area. -from Authors