Regional Forcing Mechanisms for Winter Precipitation Variability in Coastal New England

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Monday, 5 January 2015
Samuel T. Amdur IV, Williams College, Williamstown, MA; and Y. O. Kwon, C. C. Ummenhofer, and M. S. Cook

Handout (3.4 MB)

Winter precipitation variability is especially high along the coastal regions of New England, which frequently experience the brunt of extreme precipitation events. Large scale circulation regimes fail to account for the majority of this variability, and recent studies have pointed to regional influences, such as sea surface temperature (SST) anomalies, as factors in precipitation variability. The PRISM Climate Group precipitation dataset is used in conjunction with a variety of reanalysis products for the analysis period 1901-2013 to examine associations between winter (January-March; JFM) precipitation, regional anomalies in SST, and 500 hPa geopotential height anomalies. Composites of precipitation and SST were generated for the extreme SST and precipitation winters (top and bottom 10%), respectively. Both extreme SST and extreme precipitation winters are not significantly correlated with the North Atlantic Oscillation (NAO), and while extreme SST exhibits clustering on decadal timescales, its relationship with large scale modes of variability, such as the Atlantic multidecadal oscillation (AMO), is unclear. On the other hand, a statistically significant relationship is found between increased coastal New England JFM precipitation and anomalously warm SST south of Newfoundland. Furthermore, correlation analysis suggests a statistically robust relationship between precipitation and localized height anomalies east of Newfoundland, i.e. high pressure anomalies associated with the enhanced precipitation along the New England coast. Our results indicate that extreme winter precipitation in coastal New England is dynamically linked to localized blocking patterns associated with anomalously warm SST near Newfoundland.