St. Lawrence Storms Charge Maine-NH-VT Borders with Supercell Fury — SevereWX

A mesoscale convective vortex crossing from Quebec is reigniting thunderstorm activity along an outflow boundary into western Maine, northern New Hampshire, and Vermont.

SPC's Mesoscale Discussion 1613 highlights renewed development near the St. Lawrence Valley, where storms are tapping into a moist boundary layer with 70°F dew points and over 2000 J/kg CAPE. As a capping elevated mixed-layer erodes southward through 20-22Z (4-6 PM EDT), scattered storms should root deeper, evolving into supercells amid strong shear.

Key Threats:

• Large Hail: 1.50-2.50 inches (tennis ball size)
• Damaging Winds: 65-80 mph gusts
• Tornadoes: 1-2 possible with 120-145 mph peak intensity (EF2 strength)

Storms spreading east-southeast could peak through early evening, with a 60% chance of a watch. This setup echoes recent Slight Risk expansions for northern New England but zeroes in on border-area intensification.

Stay Prepared: Monitor radar closely, have multiple alerts enabled, and secure outdoor items. If severe weather approaches, seek shelter away from windows. Check SPC updates at spc.noaa.gov.