The seasonal phenomenon of “ice-out,” the date on which the ice cover of a lake, pond, or river breaks up, has been well documented for many lakes in Maine. Numerous studies from around the world have linked progressively earlier ice-out dates to climate change and sought to use ice-out records, which often pre-date accurate temperature records, to better understand the effects of climate change. Synoptic weather-typing, or the characterization of daily surface weather conditions into archetypical classes, was the chief method of analysis in an effort to derive the link between shifting weather conditions (a manifestation of climate change) and the ice-out of 20 Maine lakes. In particular, the Spatial Synoptic Classification (SSC) method was selected due to its strong record in research and local availability. So-called “polar” weather-types, specifically Dry Polar (DP) and Moist Polar (MP), make up the majority of days in winter and early spring, but the latter-half of the twentieth century has seen MP days on the decline. The loss of MP days was found to be to the gain of the comparatively warmer Dry Moderate (DM) weather-type. MP and DM days each account for about 20% of the composition of the winter-spring “superseason,” on average; thus the balance between the two weather-types represents a synoptic barometer that provides an indication of a relatively early or late ice-out.

The cryosphere has been shown to be particularly adept as a proxy for climate change by various studies. Accordingly, historical records from the field of ice phenology have been harvested by climate scientists for the express purpose of studying the temporal variation of ice phenomena, namely freeze-up and ice-out. Ice-out records from 20 lakes in Maine, U.S.A. were collected and clustered by z-score for this thesis. Rather than attempt to relate ice-out to spring air temperature or global teleconnections/oscillations, the Spatial Synoptic Classification (SSC) method was used to encapsulate several meteorological variables that could have a bearing on ice-out variation. The balance between occurrence of relatively cool Moist Polar (MP) and relatively warm Dry Moderate (DM) weather-types during the winter-spring "superseason" was found to be a synoptic barometer of whether ice-out would occur seasonably early or late. The significance of this is predicated upon the finding that quantity of DM days has steadily risen at the expense of MP days during the latter-half of the twentieth-century, in accordance with observed climatic warming during the same period. The remaining SSC weather-types, most notably omnipresent Dry Polar (DP), remained generally stable during the historical record in Maine, further undergirding the significance of the DM-MP relationship.

Master of Science