CR 72:19-27 (2017)  -  DOI: https://doi.org/10.3354/cr01444

ABSTRACT: A tornado climatology is constructed for the northeast USA (hereafter, Northeast) for the period 1950-2014. This region is highly susceptible to tornado damage as it includes dense populations in several major cities. This study provides a general climatology of tornadoes in the Northeast by exploring the spatial and temporal characteristics of the region’s tornadoes. Additionally, 86 days defined as active tornado days (5+ reports per day) are used to examine the synoptic patterns associated with Northeast tornado environments. Tornadoes in the Northeast were most frequently reported in the late spring and summer months (May to July), during the late afternoon and early evening hours, between 18:00 and 23:00 h UTC (14:00 and 19:00 h local sidereal time [LST]). Tornadoes were reported most frequently along the densely populated Interstate 95 corridor, which connects several of the largest cities in the USA. Approximately 79% of all Northeast tornadoes were given an Enhanced Fujita Scale intensity rating of ≤1. Composite synoptic maps indicate that Northeast tornado outbreaks are commonly associated with a 500 hPa trough and a surface low pressure system over the Great Lakes. Differential positive vorticity advection and warm advection contribute quasi-geostrophic forcing, modifying thermodynamic profiles making them favorable for convection. These lifting mechanisms and associated instability (represented by high equivalent potential temperature and an unstable lifted index), along with sufficient lower tropospheric wind shear, provide the ingredients necessary for severe convection.

KEY WORDS: Tornado · Climatology · Northeast USA · Severe weather