DELMARVA - Residents of Delmarva should prepare for a potentially stormy evening as a closed low across southern New England lifts northward and weakens. Shortwaves rotating around this low will pass through our region, creating conditions conducive to isolated to scattered thunderstorms.
Surface-based instability (SBCAPE) up to 2500 J/kg combined with bulk effective shear of 25-35 knots will interact with these shortwaves, providing the lift necessary for thunderstorm development. While there is some variability in model guidance regarding the exact location and coverage, there is a significant signal for convection, particularly in southern New Jersey.
Should these storms develop, we could see localized heavy rain leading to flash flooding, as well as damaging downburst wind gusts due to the presence of dry mid-level air and steeper low-level lapse rates. Additionally, some storms may produce hail. Most of the thunderstorm activity should dissipate by late evening, but a few lingering showers could persist overnight. Expect cloudy and humid conditions throughout the night, with the possibility of patchy fog.
As the closed low moves further away, a new upper-level trough will approach from the west overnight, getting closer during the day on Tuesday. This will bring increased forcing for ascent and building instability, leading to a rise in showers and thunderstorms, particularly in the afternoon. Areas with higher moisture content may experience heavy rain and localized flash flooding. The most organized thunderstorms are likely to be found across eastern Pennsylvania into northwest New Jersey, where the highest probabilities of precipitation are noted.
