The Thanksgiving 2004 Severe Weather Event across Upstate New York and New England

 

  Thomas A. Wasula and Kenneth D. LaPenta 

 

NOAA/National Weather Service, Albany, New York

251 Fuller Road

Suite B-300

Albany, NY 12203

 

Severe thunderstorms across the northeastern United States are very uncommon in the late fall and winter.  For example, Albany, New York, only averages about 3 thunderstorm days every decade in the month of November.  Severe thunderstorms producing damaging winds in excess of 50 knots (58 mph) and large hail (greater than 1.9 cm) occurred Thanksgiving morning over much of eastern New York and Western New England.  An anomalously strong low pressure system and its associated cold front focused an area of thunderstorms that developed between 1000 UTC and 1200 UTC 25 November 2004 from central New York southward into Pennsylvania and Maryland.  There were nearly two dozen wind damage reports over New York and New England from this severe weather event. Most of eastern New York and western New England broke into the warm sector of this complex weather system after 1000 UTC 25 November 2004.  A strong 500 hPa jet streak of nearly 100 knots moved northeastward from the Delmarva region on the east side of a developing negatively tilted high amplitude trough extending from Hudson Bay south to the Tennessee Valley.  Eastern New York and New England were located on the left front quadrant of the mid and upper level jet streaks with moderate divergence at 300 hPa.  A very strong low-level baroclinic zone was pushing eastward across New York at 1200 UTC with 850 hPa temperatures around -1°C near Buffalo and as high as +13°C over southwest New England. Surface dewpoints were excess of 10°C ahead of the cold front that morning.  The 1200 UTC sounding from Albany revealed convective available potential energy values (CAPE) in the 250 - 750 J kg^-1 range (Mean Layer CAPE was 637 J kg^-1 and the Downdraft CAPE value was 629 J kg^-1). The 0-6 km bulk shear values over eastern New York were in excess of 60 knots. This indicated the high potential for organized severe convection including supercells.  By 1200 UTC, a squall line developed west of the Hudson River Valley region in a low CAPE, high shear environment. This poster presentation will take a multi-scale approach analyzing the event from the synoptic-scale to the storm-scale, in order to understand the environment that caused the anomalous severe weather over the Northeast.  Observational data used in the analyses will include surface and upper air observations, satellite imagery, and Albany (KENX) WSR-88D data.  Also, high resolution initialized North American Model (NAM) data will be shown in the presentation.