AbstractWe analyze how winter thaw events (TE; T>0°C) are changing on the summit of Mount Washington, New Hampshire using three metrics: the number of TE, number of thaw hours, and number of thaw degree-hours for temperature and dewpoint for winters from 1935-36 to 2019-20. The impact of temperature-only-TE and dewpoint-TE on snow depth are compared to quantify the different impacts of sensible-only and sensible-and-latent heating, respectively. Results reveal that temperature- and dewpoint-TE for all metrics increased at a statistically significant rate (p<0.05) over the full time periods studied for temperature (1935-1936 to 2019-2020) and dewpoint (1939-1940 to 2019-2020). Notably around 2000-2001, the positive trends increased for most variables, including dewpoint thaw degree-hours that increased by 82.11 degree-hours decade-1 during 2000-2020 – about five times faster than the 1939-2020 rate of 17.70 degree-hours decade-1. Furthermore, a clear upward shift occurred around 1990 in the lowest winter values of thaw hours and thaw degree-hours – winters now have a higher baseline amount of thaw than before 1990. Snow depth loss during dewpoint-TE (0.36 cm hr-1) occurred more than twice as fast as temperature-only-TE (0.14 cm hr-1). With winters projected to warm throughout the 21st century in the Northeastern US, it is expected that the trends in winter thaw events, and the sensible and latent energy they bring, will continue to rise and lead to more frequent winter flooding, fewer days of good quality snow for winter recreation, and changes in ecosystem function.
An Historical Survey of the Late-Season Snow-Bed in Tuckerman, Ravine, Mount Washington, U.S.A.