(updated at 11:15 p.m., originally posted at 8 a.m.)
The metro region is included in a large tornado watch spanning parts of six states. The watch extends from the Mason Dixon line southwest all the way into western South Carolina and extreme northeast Georgia. From NOAA's Storm Prediction Center:
TORNADOES...HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.
The National Weather Service Forecast Office in Sterling also issued a Special Weather Statement about the severe storm threat. Here's the key excerpt:
THUNDERSTORMS ARE EXPECTED TO DEVELOP OVERNIGHT AS UPWARD MOTION INCREASES COINCIDENT WITH A VERY STRONG LOW-LEVEL JET. WIND FIELDS WILL SUPPORT ORGANIZED LINEAR STORMS CAPABLE OF DAMAGING WIND GUSTS AND NOCTURNAL TORNADOES. THE BEST CHANCES FOR SEVERE WEATHER DEVELOPMENT WILL BE AFTER 10 PM.
Based on the current storm movement (southwest to northeast) and models forecasts, storms will probably begin affecting the far southwest and western suburbs as early as between 12 p.m. and 3 a.m., the immediate metro region between 2 and 6 a.m. (toward the end of the watch period) and far eastern suburbs (not included in the watch) between 3 and 7 a.m.
The cold front associated with this historic storm has already produced more than 250 wind damage reports and spawned 21 tornadoes today alone. While severe storm reports are unlikely to be as widespread overnight, the potential exists for wind damage and isolated tornadoes.