Mechanisms of Abrupt Extreme Precipitation Change Over the Northeastern United States

Authors: Jonathan Winter*, Dartmouth College, Huanping Huang, Dartmouth College, Erich Osterberg, Dartmouth College
Topics: Climatology and Meteorology, Global Change
Keywords: Extreme precipitation, Northeast, climate variability, climate change
Session Type: Paper
Day: 4/3/2019
Start / End Time: 8:00 AM / 9:40 AM
Room: Stones Throw 1 - Granite, Marriott, Lobby Level
Presentation File: No File Uploaded

In 1996, the northeastern United States experienced an abrupt increase in extreme precipitation, but the causal mechanisms driving this increase remain poorly understood. We find that 89% of 1996–2016 increase relative to 1979–1995 is explained by only 273 unique extreme events occurring in the months of February, March, June, July, September, and October. We use daily weather maps to classify the 273 extreme precipitation events by meteorological cause (tropical cyclones, fronts, extratropical cyclones), and use reanalysis data to determine large-scale changes in the atmosphere and ocean associated with increased extreme precipitation for each classification. Results show tropical cyclones account for almost half (48%) of the post-1996 extreme precipitation increase, while fronts and extratropical cyclones are responsible for 25% and 15% of the increase, respectively. The remaining 11% is from events in the other six months of the year and extreme events that affected <5 stations. The increase in extreme precipitation from tropical cyclones after 1996 is associated with a shift to the Atlantic Multidecadal Oscillation (AMO) warm phase, higher total column water vapor, and potentially weakened steering winds. September and October tropical cyclones caused significantly more extreme precipitation during the current AMO warm phase (1996–present) than during the last warm phase (1928–1962), despite the same number of Northeast tropical cyclones in both periods. Increased frontal extreme precipitation is associated with a wavier (higher amplitude) jet stream, which likely facilitates the development of more frequent fronts through the advection of cool northern air into the American Midwest.

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