Cold-Air Damming During Significant Late-Season Winter Precipitation Events in New England

Abstract

The late cold season in New England often presents the most challenging forecast environment for meteorologists in the region. Northern New England especially experiences a wide variety of impacts from significant precipitation events which can halt transportation, disrupt economic activity, damage property, and jeopardize people’s lives. A high degree of accuracy is needed to properly identify the risks from these systems and communicate them effectively to the public. Cold air damming (CAD) plays a large role in the types of impacts significant precipitation brings. When cold air is pushed up against the eastern side of the Appalachians, these areas are at risk of more impactful wintry precipitation from significant precipitation events. Much of the existing CAD research focuses on the southern Appalachians and does not directly investigate the relationship between CAD and such systems. This study modifies a previous Cold Air Damming Index (CADINX) to quantify the strength and duration of CAD events leading up to and during significant late-season precipitation events in northern New England. Late-season winter precipitation events were identified between 1 March and 30 April during a 10-year period from 2014 to 2024. CADINX values were calculated for three locations, Concord, NH Municipal Airport (KCON), Waterville, ME Robert LaFleur Airport (KWVL), and Eastern Slopes Regional Airport in Fryeburg, ME (KIZG) in tandem with a precipitation site in Tamworth, NH. Statistics regarding the duration and strength of CAD, precipitation type and rate, and storm system type and track were subsequently collected. This, combined with composite analysis and a case study on a particularly long event from 3 to 6 April 2024, revealed that CAD is frequently associated with significant precipitation events in this region. Fifty-one events were identified, of which 19 occurred simultaneously at multiple stations resulting in 32 unique events across the three central locations. Roughly 60% of hours of precipitation also had CAD, with 80% of precipitation being snow, freezing rain, or a mix. The majority of significant precipitation events were coastal lows, of which those with less intense pressure gradients that remained offshore being the most favorable for extended CAD events. CAD frequently peaked shortly before precipitation onset, with a secondary peak starting in the second half of the precipitation systems across all CAD events. Future work will focus on identifying how well NWP models represent these findings and expanding the temporal and seasonal duration of the CAD-precipitation relationship.