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Convective Storm Structures and Ambient Conditions Associated with Severe Weather over the Northeast United States Kelly A. Lombardo and Brian A. ColleBy Danielle LaFlamme and Erin PrattOutlineIntroduction Data and MethodsWindHailTornadoesCellularLinearNonlinear ComparisonsSummaryIntroductionSevere weather much less common over Northeastern U.S. than over Great Plains and MidwestNo studies have been done to identify convective structures associated with severe weather over the Northeast or over the coastal NortheastStudies have shown how synoptic conditions support severe weather over the NE:500 hPa flow, cyclonic directional wind shear, LL moisture, CAPE > 3000 J/kgElevated mixed layerTopography

IntroductionWhat is the type and frequency of severe weather associated with various convective organizational structures over the Northeast? How does this compare to the central U.S.?How does the type of severe weather produced by specific convective organizational structures over the entire northeastern U.S. compare with that over the Northeasts southern coastal region?What are the lifting mechanisms and thermodynamic conditions associated with severe weather over the coastal region, and how do they vary between convective organizational structures (i.e., cellular, linear, nonlinear)?Data and MethodsTwo datasets tornado and wind/hailWind/hail May-August 2002-2007NE wind, coastal wind: 276, 226NE Hail, coastal hail: 195, 116Tornadoes May-August 1996-2007NE tornadoes: 125Coastal tornadoes: 27Used 2-km NOWrad reflectivity imagery, SPC and NCDC storm report archivesFor coastal regions, constructed spatial composites of ambient conditions using NARRGenerated box-and-whisker plotsData and MethodsDefinitions:Cellular convection individual cells, clusters of cells and broken linesLinear systems bow echoes, squall lines with trailing stratiform rain/leading stratiform rain/parallel stratiform rain/no stratiform rainNonlinear systemsArea studied:

Wind EventsNE:Most common event, 68% of reportsCellular: clustersLinear: linear convection with no stratiform rain/with trailing stratiform rainNonlinear: 8 more events than clustersCoastal:Cellular: clustersLinear: linear convection with no stratiform rain/with trailing stratiform rainNonlinear: 11% of wind events

Hail events1/3 of all eventsNE:Cellular: clustersLinear: linear convection with no stratiform rain/with trailing stratiform rainNonlinear: slightly fewer events than clusters of cells Coastal:Cellular: clusters and individualLinear: linear convection with no stratiform rain/with trailing stratiform rainNonlinear: least number of hail eventsTornado EventsNE:Cellular and Linear types produce the same number of tornadoes, much more than non-linear

Coastal:Equal chance from cellular, linear and non-linear (probably because of limited sample size)

Cellular Events

Linear Events

Nonlinear Systems

Comparison Between Organizational Structures

Comparison of Convective Parameters in NE to Central U.S.MUCAPE for NE coastal cellular events similar to MLCAPE for Great Plains nonsupercellsFor linear events, NE MUCAPE half as large as Great Plains MLCAPE, however coastal MUCAPE is similar to Great Plains MLCAPEMean shear values for linear systems over the coast are less than shear values in the Plains for derecho-producing MCSsNE severe events develop under weaker CAPE and vertical wind shear than the central U.S. Synoptic-scale lift important to release more moderate instability in NE

Comparison of Organizational Structures in NE to Central U.S.Over NE and Plains, nonlinear events produce 29% of severe weather eventsCellular convection responsible for more severe events over central U.S. than over NELinear convection responsible for more severe events over NE than central U.S. Severe wind events over NE come from lines with trailing stratiform, while over Plains come from bow echoesSmall hail comes from bow echoes and broken lines over central U.S., while severe hail comes from broken linesIn NE, clusters of cells and lines with trailing stratiform produce more hail than bow echoesBroken lines and lines with parallel stratiform produce tornadoes over Plains, bow echoes produce tornadoes over NESummaryNortheast:Severe wind: equally likely to be produced by all three convective structure typesHail: cells produce more than linear or nonlinearTornadoes: primarily come from cells and linesCoast:Severe wind: typically from cells and linesHail: greater prevalence for hail events from cellsTornadoes: no one structure is favored

SummaryUnderstanding interactions between convective storms and Northeastern U.S. complex terrain/the Atlantic coastal boundary is important because forecasting severe weather over the NE coast is difficult due to subtle differences in conditions compared to the central U.S. Questions?