Significant Coastal Impacts to the Eastern Seaboard; Hurricane Nolo to Impact Hawaii

A Nor'easter will bring significant coastal impacts to the Mid-Atlantic and New England through the weekend. Moderate to major coastal flooding, heavy rain, strong winds and high surf expected. Hurricane Nolo is expected to stay just south of the Big Island of Hawaii. However, strong winds and heavy rainfall may bring life-threatening, catastrophic flooding and mudslides through the weekend. Read More >

November 5, 2007
The Mini-Supercell / Marginal Hail Event of November 5, 2007

Overview: A quick-moving cold front moved across the ILN CWA during the afternoon of 11/5/07. A cool late-autumn airmass was in place ahead of the front (temperatures in the upper 50s and lower 60s), which inhibited any surface-based instability. However, very weak elevated instability existed above the stable boundary layer (MUCAPE <500 J/Kg lifted from 800 hPa). In addition, shear ahead of the front was high, with 0-6 km shear around 60 kt, and 0-3 km helicities ranging from 250-500 m²/s².
As the front entered ILN's CWA, numerous thunderstorms developed and quickly took the form of elevated mini-supercells. The cores of the storms were small and were generally confined to below 15,000 feet, and none of them extended above the -20 °C level. However, many of the storms exhibited weak midlevel rotation, and almost all storms with rotation ended up producing severe hail. The high 0-3 km helicity favored midlevel mesocyclones, which led to significantly stronger dynamically-induced updrafts. The air mass in place was cool and freezing levels were low, so these meso-induced updrafts grew within the hail-growth zone of -10 to -30 °C, and large hail was the result. Because of the low freezing levels, hail was able to make it to the surface without much melting.