The extreme weather events in the US that occurred in late October and early November of 1991 known as the “Perfect Storms” transpired during a highly amplified and anomalous large-scale flow regime transition. After this regime transition the flow remained amplified and assisted in the development of two meteorologically significant and “perfect” storms. The purpose of this presentation is to document the life cycles of these twin extreme weather events via a multi-scale diagnostic analysis and to examine the linkages between the storms and the intraseasonal variability of the observed large-scale flow regimes.

The first of the Perfect Storms began with an extratropical, baroclinic cyclone east of Nova Scotia on 28 October embedded downstream of a highly amplified mid-level trough-ridge pattern over the US. Its deep circulation quickly became the foremost feature in the northwest Atlantic as it overtook Hurricane Grace to its south. The extratropical cyclone continued to strengthen to 972 hPa as it propagated westward towards the US and then subsequently weakened as it performed a counter-clockwise loop in the far western Atlantic beneath the building ridge. The warm waters of the Gulf Stream then excited convection within the center of the Perfect Storm, yielding the development of the Unnamed Hurricane on 2 November.

The second of the Perfect Storms began as a positive upper-level potential vorticity anomaly rotating through the trough in the western US. Its surface reflection formed as a weak center of low pressure in extreme western Gulf of Mexico that strengthened and propagated northward as the mid-level trough tilted negative on 1 November. A strong (1050 hPa) surface anticyclone propagating southward from Canada provided anomalously cold air (~ -3σ) that aided in giving Minnesota its earliest and heaviest snowfall totals, setting the state record of 93.7 cm in Duluth, MN. By the end of the life cycles of these two storms, the large scale flow regime had once again reversed.

The presented research will focus on (1) the development and life cycles of the two Perfect Storms, (2) linkages between the two Perfect Storms and the large-scale flow regime as derived from atmospheric teleconnections, and (3) impacts of the observed intraseasonal extreme weather events on seasonal climate anomalies.