Nighttime Dangerous and Extreme Heat Events During Summer Months in the Northeast

Title: Nighttime Dangerous and Extreme Heat Events During Summer Months in the Northeast

Authors: Emily Case¹, Neil Laird², Augusta Williams³, and Caitlin Crossett⁴

1 Ohio University

2 Hobart and William Smith Colleges

3 Upstate Medical University

4 University of North Carolina at Ashville

Abstract

Extreme heat poses many health risks and past studies have found distinct meteorological and health impact differences between daytime and nighttime heat waves. Daytime heat waves are more common with intense solar radiation, less humid air, and cloudless conditions. Nighttime heat waves are especially impactful and pose increased health risks, especially with increased cloud cover and higher humidity. This research used hourly surface weather observations from 19 stations within the Northeastern United States for summer months during a 40-year period (1980–2019) to examine the spatiotemporal variation of nighttime extreme heat events. Specifically, the nighttime hours from 3 UTC to 9 UTC (11 PM to 5 AM EDT) were used to identify nighttime extreme heat hours (EHHs; defined when the nighttime temperature exceeded the 90^th percentile temperature derived from nighttime temperatures during the study period), extreme heat waves (EHWs; defined as three or more consecutive nights that have at least one EHH), and dangerous heat hours (DHHs; defined when the nighttime temperature exceeded the 99^th percentile temperature derived from nighttime temperatures during the study period). Nighttime EHHs and EHWs were examined for each decade (1980s, 1990s, 2000s, and 2010s). The 2010s had the largest number of summer nighttime EHHs, DHHs, and EHWs. The 2000s had the least amount of nighttime heat-related events. Generally, a large number of nighttime EHHs, DHHs, and EHWs occurred in West Virginia and central Pennsylvania with locations near Lakes Erie and Ontario, as well as southern New England (e.g., Connecticut), having fewer.