Wednesday, August 24, 2011

Severe Threat Today

Favorable atmospheric dynamics are lining up for strong and severe thunderstorms toward the evening hours tonight.  Our entire area is under a slight risk for severe weather which would include large hail, damaging winds and possibly isolated tornadoes. 

Forecast Discussion: (Because you asked...)

Potent upper level shortwave and eventual closed low will work into the Great Lakes region sweeping a cold front across the area late tonight.  An increase in the 500 mb winds (~50kts) will provide ample shear for severe thunderstorms and isolated supercell storms.  Convection will be aided by moist and unstable atmosphere that will provide CAPE values (a common measure of instability) in excess of 4,000 j/kg.  This highly unstable atmosphere set off by an advancing cold front and moderate shear will likely allow for the formation of an MCS (Mesoscale Convective System) possibly in the form of discrete supercells initially followed by a squall line across most, if not all of our area.   

The timing on the storm will be after 5 PM, as a cap in the atmosphere is expected to hold until then.  Initial supercell thunderstorms would be the most likely culprit of an isolated tornado with the evolution of this event focusing more on damaging winds and large hail as the evening progresses.   Stay tuned for details!