Analysis of Late Summer Heat Waves in the Northeast US

The climatological temperature maximum and frequency of heat waves, defined as three or more consecutive days of maximum temperatures at or above 32 degrees Celsius, often peak around mid to late July in the Northeast United States. However, numerous notable heat waves have occurred in late August into early September, including 1953, 1973, and to a lesser extent 2015. An analysis of daily means of 500 hPa geopotential heights from the NCEP-NCAR Reanalysis dataset over a 67–year period (1948–2015), in addition to surface temperatures from numerous stations east of the Mississippi River, shows a secondary peak in mean temperatures, geopotential heights and heat wave frequency over the Northeast and Ohio Valley, and to a lesser extent in the Southeast, during the late summer. This peak is most evident in late August, both on the synoptic scale and on a localized scale in the selected stations. Composite 500–hPa geopotential height and surface analyses of the warmest late August into early September time frames exhibits an anomalous Western US trough and Eastern US ridge, and an antecedent cold Canadian surface anticyclone transitioning into a warm subtropical anticyclone near the eastern US.