Analyzing the April 1, 2023 Mid-Atlantic Severe Weather Outbreak: A Meteorological Case Study and Performance Overview of National Weather Service Weather Forecast Office Philadelphia/Mount Holly

The Philadelphia/Mount Holly (PHI) Weather Forecast Office (WFO) serves a diverse range of counties across New Jersey, Pennsylvania, Delaware, and Maryland, all situated within the Mid-Atlantic region. On April 1, 2023, a significant severe weather outbreak occurred, causing extensive wind and tornado damage. This event spawned a total of nine tornadoes within the County Warning Area, resulting in both fatalities and widespread damage.

This study examines the synoptic and mesoscale dynamics that underlie the weather event on April 1st and its forecasted evolution. The main goal of the analysis is to understand the factors that contributed to the event and to gain insights that could aid in understanding similar events in the future. This event featured a strong mid-upper level jet, unseasonably strong instability, high shear, high storm relative helicity, and strong updraft helicity tracks, which all contributed to the enhancement of tornado activity.

This study also presents a review of how WFO PHI staff performed during the events of April 1st. The Philadelphia/Mount Holly office issued eight Tornado Warnings, 17 Severe Thunderstorm Warnings, and six Special Marine Warnings during the event, achieving a 92%Probability of Detection, 32% False Alarm Ratio, with an average lead time of 24 minutes for all reports. Notably, tornado warnings were in effect for eight of the nine tornadoes, with just one tornado event eluding detection due to the challenging linear storm mode. The office’s early recognition of favorable synoptic patterns allowed WFO PHI to provide excellent decision support service to core partners and the public. The office was able to provide awareness about the potential hazards including damaging wind, large hail, and tornadoes, all with multiple days of lead time. Timely communication provided through partner emails before, during, and after the event along with continuous updates on social media ensured that the public remained well-informed throughout the event.