Predictability Challenges Associated with Significant North American Weather Events during Winter 2014–2015

Lance F. Bosart

The University at Albany/SUNY

Thursday, Feb 11, 2016, 2:00 pm
DSRC Room 1D-403


Abstract

Winter 2014–2015 was marked by the coldest November weather in 35 years east of the Rockies and record-breaking snowstorms and cold from the eastern Great Lakes to Atlantic Canada in January and February 2015.  Record-breaking warmth prevailed across the Intermountain West and Rockies beneath a persistent upper-level ridge. Winter began with a series of arctic air mass surges that culminated in an epic lake-effect snowstorm occurred over western New York before Thanksgiving.  Winter briefly abated in part of December, but returned with a vengeance between mid-January and mid-February 2015 when multiple extreme weather events that featured record-breaking monthly and seasonal snowfalls and record-breaking daily minimum temperatures were observed over parts of the Northeast.



The recurvature and extratropical transition (ET) of Supertyphoon (STY) Nuri in the western Pacific in early November 2014, and its subsequent explosive reintensification as an extratropical cyclone (EC), disrupted the North Pacific jet stream and downstream Northern Hemisphere (NH) circulation, produced a high-latitude, diabatically enhanced omega block over northwestern North America, and triggered downstream baroclinic development and the formation of a deep trough over eastern North America. Predictability was limited to several days over the North Pacific prior to the ET/EC of STY Nuri, but improved to ~10 days over North America subsequent to diabatically enhanced high-latitude omega block formation. 



Large-scale flow amplification in mid-January 2015 resulted in the formation of high-amplitude ridges over northeastern Russia, Alaska, western North America, and the North Atlantic, and the formation of high-amplitude troughs over the eastern North Pacific and eastern North America.  This amplified flow pattern supported the occurrence of frequent heavy snowstorms, including blizzards, over parts of the northeastern United States and adjacent Atlantic Canada during the latter part of January and much of February 2015. Predictability uncertainty was enhanced when the location of the western and northern edge of the forecast snow shield was juxtaposed with the populous I-95 corridor. 

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