A new liveblog has been published to ensure folks with slower internet connections can load the diary and comments. This one will no longer be updated.
The Storm Prediction Center has issued a rare "high risk" outlook for much of the Ohio Valley this afternoon, as a major tornado outbreak is beginning to develop at this hour. Numerous tornado watches are in effect, two of which are "Particularly Dangerous Situation" Tornado Watches -- enhanced wording to convey the violent, long-lived tornadoes these storms are expected to produce. In addition to the tornadoes, wind gusts over 70 MPH and hail at or above the size of tennis balls (2.50") is possible in the storms that develop.
The storms are moving into an environment ripe for explosive development and rotation. The 0-6km bulk shear (a calculation of how much the wind changes speed and direction between the surface and 6 kilometers above ground level) over central Kentucky is up around 70 knots, with 40 knots about the point where the environment is able to support a healthy supercell thunderstorm.
The storm relative helicity (a measure of how much rotation a thunderstorm's updraft is able to attain...crucial to the development of tornadoes) is well above the threshold needed for significant tornadoes to develop, with the latest numbers approaching 500+ along the leading edge of the storms in western Kentucky and southeastern Illinois. A value of 450 means that the thunderstorm is capable of producing and supporting violent EF-4 or EF-5 tornadoes -- both of which are distinct possibilities this afternoon and evening. Storm relative helicity values are expected to climb eastward throughout the day into the high risk area.
There is a large area of partly cloudy skies in the warm sector right now, which is allowing the surface to heat up greatly and add fuel to the fire. The model indicates that the latest CAPE (Convective Available Potential Energy...the amount of energy possible a parcel of air would have if it is able to lift up through the atmosphere; the higher the CAPE, the better) is up around 2500, which is more than sufficient lift to sustain thunderstorm development.
Right now there are two areas of thunderstorms -- the ones that will become problematic today are in southern Illinois and the southern tip of Indiana. As they continue eastward, they should grow in number and explosively develop. The other older line is in eastern Tennessee right now, prompting numerous tornado warnings for the Appalachians.
It's going to be a bad day. Again...it won't be as bad as April 27th or 1974, but by nightfall we'll see some significant damage and probably some deaths. Help to prevent those deaths by watching the skies and advising your loved ones to do the same.
Outlook:
Probability of a tornado within 25 miles of any one point:
Tornado Watch #57:
Tornado Watch #58:
