There is an elevated tornado risk today into tonight and tornado warnings have already been issued in the Maryland suburbs (Howard, Carroll and Baltimore counties). What's the cause?
It turns out there is an unusual amount of spin in the atmosphere due to changing winds in the low layers of the atmosphere (between the surface and about 10,000 feet). We refer to this turning of the wind with height (in both direction and speed) as wind shear. There's also a fair amount of instability - as a result of cooler air moving into the region at high levels and warm air coming up from the south at low levels.
As NOAA's Storm Prediction Center explains in more technical terms:
STRONG VERTICAL SHEAR WILL BE IN PLACE OVER [PARTS OF THE MID-ATLANTIC] AS THE UPPER WAVE APPROACHES FROM THE SOUTHWEST. A POCKET OF COOLER TEMPERATURES ALOFT AND STEEPENING LAPSE RATES MAY PROVIDE SUFFICIENT THERMODYNAMIC SUPPORT FOR THE DEVELOPMENT OF ISOLATED STORMS CAPABLE OF DAMAGING WINDS OR A TORNADO.
We'll keep a close eye on storms this afternoon and tonight - as more tornadoes may develop.