July 2020 was record hot for much of the Mid-Atlantic and Northeast. Sizzling temperatures and sultry humidity baked the Acela corridor for most of the month, with heat indices rising into the triple digits and making conditions all the more unbearable. The entire Lower 48 experienced temperatures near or above normal during July, the toasty temperatures becoming routine as human-induced climate change continues to take is toll. The month ranked as the 11th warmest on record overall, according to the National Oceanic and Atmospheric Administration.

Seven states — Virginia (tie), Maryland, Delaware, Pennsylvania (tie), New Jersey, Connecticut (tie) and New Hampshire — all clinched the top spot for their sweltering July heat. Records date back to 1895. The heat was ubiquitous along the East Coast, with states east of the Appalachians recording a top five warmest July except Georgia and South Carolina.

High pressure stalls with sizzling heat

July temperature rankings by state out of 126 years of data. (NOAA/NCDC)
July temperature rankings by state out of 126 years of data. (NOAA/NCDC)

Paramount to the heat was a sprawling dome of high pressure, which deflected cooling weather systems to the north. Westerly or northwesterly winds at the mid levels of the atmosphere helped pump in air from the core of this “heat dome,” also suppressing cloud cover or a cooling onshore flow.

Overall, the magnitude of the heat wasn’t overly impressive for most of the Northeast, but its duration was surprising. Manchester, N.H., hit 90 degrees 15 days out of the month, including on July 19, when the high was 98. That’s close to the average number of 90 degrees that would occur in a year.