Date of Award
Bachelor of Science
Atmospheric and Environmental Sciences
Brian Tang, Ph.D.
Ross Lazear, M.S.
A serial derecho impacted Upstate New York and western Massachusetts on the afternoon of 7 October 2020, resulting in 120 damaging wind reports alonga 515-km swath. The magnitude and extent of this event was unexpected and not well forecast, motivating a closer examination. This study seeks to better understand the conditions prior to and during the derecho to diagnose what led to such a damaging wind event. The synoptic forcing for this event was an upper- level jet with a broad, negatively tilted trough over the northeast U.S. and southeast Canada. The upper-level pattern provided forcing for a 990-hPa surface low in southern Quebec with a cold front draping southwest across New York. A mesoscale convective system (MCS) formed as the cold front progressed eastwardalong the Mohawk Valley. The pre-convective environment was characterized by high shear and low CAPE with < 500 J kg-1 CAPE and > 35 m s-1 0–6-km shear.
The local evolution was analyzed using New York State Mesonet surface observations along the Mohawk Valley, in the propagation direction of the derecho. These observations show that surface warming ahead of the cold front increased the temperature gradient and decreased stability immediately prior to the derecho passage. Factors that may have contributed to this warming and destabilization include decreasing cloud cover, adiabatic warming via downslope winds, and channeling of warm air northward in the Hudson Valley. Models wereunable to capture the rapid destabilization immediately preceding the frontal passage resulting in poor convective structure in the forecast.
Couillard, Maxim, "Observations and Analysis of the 7 October 2020 Derecho" (2022). Atmospheric & Environmental Sciences. 25.
Available for download on Thursday, December 01, 2022