How are Mid-Winter Thaws Changing at the Summit

 
Ethan Rogers – Penn State University, Meteorology
Observer Guide –Adam Gill
Mentor – Jay Claussen – Cold RegionsResearch and Engineering Laboratory, Hanover, NH

Skier and winter recreationalists dread those episodes of warm, rainy conditionsin the middle of winter. Furthermore, mountain ecosystems rely upon relatively consistent cold winters with a thick insulating snowpack.Recentresearch has examined how winter temperature and precipitation has changed in the Northeastwith a focus on the lower elevations. But weather and climate can vary substantially between the low elevations and the higher elevations of the Northeast. This research examines how “melt events” are changing at Mount Washington.

Intern Ethan Rogers studied how these melt events have evolved from 1935-2019. He examined four key metrics: 1) number of hours above 32F, 2) number of melt-degree-hours(the cumulative number of degrees above 32F each hour), and 3) the number each winter and 4) duration of melt events. He focused on melt events during the months that are climatologically below freezing: December-February.

Results revealed that although there is no significant change in the number of melt events each winter, they are becoming warmer and longer, especially in the last 40 years. The average number of melt-degree-hours per winter has nearly quadrupled from about 100 to nearly 400 over the 85-year period. The average number of hours above 32F has doubled from ~50 hours to just over 100 hours. Futureresearch will examine these same metrics using dewpoint temperature – which is a stronger indicator of melt.

The number of hours each winter (DJF) that were above freezing at the summit of Mount Washington from 1936-2019. The red line is a 10-year running average.

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