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Overview

The day before the event (August 6), an upper trough was located over much of the eastern CONUS, with strong ridging centered over the southern Rockies. One shortwave was located just east of Chicago on the morning of the 6th. At the surface, a weak cold front stretched from Quebec to MO/IL. By the morning of August 7th, the trough started to take on a negative tilt as the aforementioned shortwave approached the Mid-Atlantic from the west. At the surface, troughing was developing across the VA/NC Piedmont, while the true cold front was well to the NW. Closer to our area, winds were S/SSW with temperatures (and dew points as well) starting off in the low-mid 70s. It quickly warmed up during the morning under partly-mostly sunny skies. By 17z/1 PM, temperatures had risen into the upper 80s-low 90s across the area, with dew points still in the low-mid 70s. The atmosphere became very unstable (especially for the Mid-Atlantic), with SBCAPE values of ~3000 J/kg west of I-95, with values approaching 5000 J/kg in areas near the Chesapeake Bay/Atlantic Ocean (due to slightly higher dew points in the area). This was in spite of relatively modest mid-level lapse rates. As the shortwave passed just to our north, mid-level (500 mb) winds were out of the SW at 30-45 kt (highest near the coast). This resulted in Effective Shear values of ~40 kt over SE VA (where there was a little bit of localized backing in the surface wind field). Effective shear values were 20-35 kt elsewhere.

Thunderstorms (a couple that were severe) quickly developed across the southern VA/northern NC Piedmont by early afternoon. Semi-discrete cells continued to track to the east. As the storms approached Hampton Roads/NE NC (the area mentioned above with the highest instability/shear), they quickly grew into an organized line by 4 PM. As the line crossed the southern Chesapeake Bay/Norfolk/Chesapeake, there were quite a few reports of 50-65 mph wind gusts. In addition, storms trained over the Norfolk/north Chesapeake/NW VA Beach area for around an hour between 4-5 PM. The very high rainfall rates associated with these storms resulted in 2 inches of rain at Norfolk International Airport in just 31 minutes...from 4:20 to 4:51 PM. This prompted a Flash Flood Warning to be issued, and there were several reports of impassable roads/cars stuck in Norfolk and the far northern sections of Chesapeake. In addition, quarter size hail was reported in Norfolk with a discrete cell that formed just ahead of the line. The line continued to push toward the coast during the evening hours. One more isolated severe thunderstorm tracked across Louisa/Fluvanna/Goochland Counties from 11 PM-1230 AM.

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