Intensifying St. Lawrence Storms Unlock Surface-Based Supercells in New England — SevereWX

Intensifying thunderstorms near the St. Lawrence Valley are poised to evolve into surface-based supercells as they push into western Maine, northern New Hampshire, and Vermont this afternoon.

A mesoscale convective vortex is tracking east-southeast across the Maine-Quebec border, with its trailing outflow boundary sparking renewed development. While storms near the vortex core have faded, fresh activity along the boundary's cool side is gaining steam, drawing on a moist boundary layer with dewpoints near 70°F and CAPE exceeding 2000 J/kg.

The key: an elevated mixed layer (EML) cap is gradually eroding southward across southern Quebec and the U.S. border by 4-6 PM EDT (20-22Z). This will allow storms to root deeper into the unstable air mass, supported by strong deep-layer shear favoring supercell structures.

Expect scattered supercells spreading into the international border vicinity, packing:

• Large hail: 1.50-2.50 inches (golf ball to tennis ball size)
• Damaging winds: 65-80 mph gusts
• Tornadoes: Potential for 1-2 with peak intensity 120-145 mph (EF2-EF3)

SPC's Mesoscale Discussion 1613 flags 60% watch odds through 2015Z. Peak threats align with the 141815Z-142015Z window.

Stay prepared: Monitor radar closely, secure outdoors, know your safe spot, and have multiple alert sources ready. Northern New England's severe window peaks soon—don't get caught off guard.