Nice compact zone of weakness in the upper air layers formed in the western and northern Piedmont...aloft were conditions suitable for quick and strong vertical development. Warm moist air rises, finds enough instability aloft to keep rising and creating heavy localized rain shafts...then the air diverges aloft, flows back to the ground, and then you have leftover storm boundaries that uptake the air, and find once again the unstable 'hole' in the atmosphere...and so they blossomed and 'passed the hot potato' of storminess along a rough line of cells that sprang to life with amazing quickness. All this on January 5th, and not really in the forecast to have happened the way it did.
Not a rare event, mind you, just uncommon and not 'normal' per se (had a strong batch of thunderstorms move through the southern Piedmont just last Sunday morning, too). The rapidity of the cell development in some areas last night was something to watch on the radar screen. I captured some radar grabs for you to click on and enlarge if you'd like to take a look at last night's activity. FYI, the 2-D shots are Level 3 data and the 3-D scans are Level 2 data run through Gibson Ridge software.
~9:30pm volume scan of steady rains and 'hot spot'
~9:36pm 'lit volume' scan of thunderstorm
(lightning data not displayed)
~9:44pm 'volume scan' of heavy (red) rain towers, downbursts
(looking south toward Greensboro and Winston Salem)
Cookin' with gas - good vertical uplift just before 10pm
(northern Guilford County, southern Rockingham County)