Analysis of the July 29th, 2023, Major-Impact Severe Weather Event in the National Capital Region

The severe thunderstorms that moved across the Washington DC Metropolitan Area and southern Maryland during the afternoon and evening of July 29th, 2023, produced the most impactful severe weather for the region since the June 2012 derecho. While this downdraft-driven event differed from the derecho in terms of coverage of significant wind damage, the impacts were much the same.

Excessive heat and humidity precluded the storms for a few days. This energy combined with a strong surface-based cold front and a mid-level shortwave trough provided the background support for these storms. As the forcing moved over a residual pressure trough just east of the Blue Ridge Mountains and over 3,000 J/kg of surface based convective available potential energy (CAPE), convection started to quickly expand in coverage. Dozens of updrafts quickly developed and congealed into a linear segment with embedded macrobursts and microbursts. This caused localized wind gusts of 60-85 mph, followed by sustained winds of 50-60 mph for upwards of 30 minutes, leading to significant damage.

Although no tornadoes were confirmed and the longevity and areal extent of this thunderstorm complex did not meet the definition of a derecho, the winds and resulting damage were comparable in impacts. Wind gusts exceeded 80 mph, toppling thousands of trees onto structures, vehicles, and roads. Structural damage affected houses and buildings, and over 300,000 customers in the greater Washington DC Metropolitan Area lost power. Some customers remained without power for upwards of one week, while crews worked to clean up the tree damage along major commuter arteries and restore power.

This study will focus on the meteorological factors driving the impacts of this event by examining machine learning guidance, NWS outlooks, and impact-based decision support services provided in the days leading up to the event.