New York and New England Significant Hail Climatology and Environmental Analysis

Significant hail, defined as greater than 50.8 mm (2 inches) in diameter, is rare in the Northeast, encompassing New York (NY) and New England, but can pose a considerable threat to life and property. According to NCEI Storm Data, NY and New England average 3.7 significant hail events (1 report = an event) per year, totaling 275 events between 1 January 1950 and 29 February 2024. The vast majority of significant hail reports (~96%) occur between May and August. Despite the elevated threat potential of significant hail events, NWS offices across the Northeast struggle to accurately predict such events in severe thunderstorm warnings. Since Northeast NWS offices began explicitly forecasting hail size in severe thunderstorm warnings in 2015, only 1 out of 49 significant hail events in the Northeast was warned for hail of significant size or larger. While considerable research exists on radar signatures indicative of significant hail, this study aims to improve our understanding of the pre-convective environments and synoptic to mesoscale features associated with significant hail in the Northeast.

The pre-convective environments for the events that produced significant hail were assessed across various pressure levels using ERA v5 data. A composite of synoptic-scale setups revealed upper-level ridging over the Rocky Mountains, troughing in southern Canada, zonal flow over the Northeast, and a 300-hPa jet streak over southeastern Canada, with its poleward entrance region situated over the Northeast. The average 700 to 500 hPa lapse rates ranged between 6.5 and 7.0 °C/km, which is unusually steep for the Northeast. Most Unstable CAPE values approached 1500 J/kg, with 30 to 40 kt of surface to 500 hPa shear on average for these events. Two cases from June and July 2011 were compared to the synoptic composites in order to highlight additional environments that were conducive to significant hail in NY and New England.