14A.2 Climatology of November Snow Days in the Lake Michigan Region: Is the Decrease in Lake Michigan November Snowfall Frequency Mostly Due to Lake-Effect Snowfall, or Synoptic Systems?

Thursday, 14 January 2016: 3:45 PM
La Nouvelle A ( New Orleans Ernest N. Morial Convention Center)
Craig Clark, Valparaiso Univ., Valparaiso, IN; and K. Goebbert, B. Ganesh-Babu, R. Connelly, A. Young, E. Delap, K. Heinlein, A. VanDe Guchte, Z. Sefcovic, A. L. Caruthers, T. J. Elless, A. Lyza, S. Fingerle, D. Koning, A. Carne, A. Krull, K. M. Zigner, and M. Haynes

Previous assessment of Lake Michigan basin snowfall characteristics since 1950 revealed a marked decrease in November snowfall frequency in recent decades, which has been driven by a decreased frequency of cold Novembers during the period. The change has been greatest in the eastern and southeastern sub-regions, implying a diminution in the frequency of lake-effect snowfall. However, the proportional decrease is similar in the western sub-regions, and the adjudication of lake-effect and synoptic system contributions to snowfall is a challenge. Here, based on the snowfall from forty-seven locations and visual inspection of maps from NCEP/NCAR Reanalysis and the historical Daily Weather Map series, 937 snow days are classified as primarily synoptic, lake-effect, both, insignificant, remnant or unclear. Results show that roughly half of the November snowfall in the eastern sub-regions is due to lake-effect snowfall, but a precise adjudication is vexed by cases with lake-enhanced system snow and other instances of synoptic and lake-effect snowfall occurring within the same day. In terms of the decreasing November snowfall frequency, both synoptic and lake-effect snow days have decreased in recent decades. While the change in lake-effect snowfall dominates east of the lake, the regional proportional decrease of snow days with synoptic and lake-effect classifications is similar. This suggests that warmer Novembers reduce both the likelihood of snowfall as mid-latitude cyclones traverse the region and the frequency and/or longevity of lake-effect snowfall during the cold air outbreaks which follow.
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