Tropical Moisture Will Bring Heavy to Excessive Rainfall with Possible Flooding This Week

Tropical moisture will surge over the southwest into the central U.S. this week with several days of heavy to excessive rainfall which may bring limited to considerable flooding. Isolated severe thunderstorm gusts and a couple of tornadoes will be possible from southeast New Mexico into west Texas. 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.