A majority of significant tornadoes (F2 or greater damage) have been associated with STP values greater than one.
The latest data suggests the greatest area of concern on Wednesday afternoon and evening will be across the following areas:
Northern Virginia, east of the Blue Ridge
Baltimore, central and southern Maryland
Have a plan of action of what to do in a tornado, especially for those of us without basements.
Excellent information here: https://www.ready.gov/tornadoes