Climatology and Recent Changes in the Occurrence of Freezing Rain throughout the Laurentian Great Lakes Region
September 8, 2025Author(s): DelPizzo, J., Baule, W.J., Tobias-Tarsh, L., Notaro, M., Rood, R.B.
Abstract
Freezing rain (FZRA) events have expensive and sometimes deadly effects on major population centers in the Great Lakes region (GLR) of North America. This paper investigates changes in the spatiotemporal nature of FZRA. The work extends the spatial and temporal record of a previously published, but now dated, Great Lakes FZRA climatology (1976–90) to analyze trends and their underlying reasons by utilizing observations made through 2020. To isolate regional trends and determine changes in the synoptic-scale processes driving them, a k-means objective clustering algorithm is applied to pressure anomaly maps and records of FZRA observations to create three archetypal synoptic weather patterns associated with FZRA. A northward shift in FZRA incidence is found across the GLR on an annual basis, with an increase in FZRA occurrence in January and April and a decrease during March. Regionally, the largest trends were a decrease since 1979 throughout Pennsylvania, upstate New York, and the St. Lawrence Lowlands of Canada and an increase in the southern reach of Manitoba, Ontario, and Quebec and the low-lying Atlantic Coastal Plain of New York. The geographic location of the low three synoptic patterns associated with FZRA events remained similar between 1979 and 1999 and 2000–20, though changes to their intensity allowed for enhanced warm air advection. We suggest that this, combined with rising temperatures in a nonstationary climate and a subtle northward shift in some cyclones, was responsible for an observed northward shift in FZRA.