Nightly News | May 16, 2013
>> weather channel meteorologist mike seidel also part of our team. this was a long windup. a 26-minute siren blast will get your attention. the problem is, so many structures are no match for an f4.
>> reporter: that's true. you know, it's been a long time coming. we've had a quiet spring. this is peak of tornado season , brian . so far since march 1, we've only had 22% of the average number of tornadoes. that did change late yesterday here in north texas . take a look at the ingredients. upper level wind support, cold air aloft over this warm, humid air at the surface. that is the perfect setup for instability. also notice the wind direction aloft. west/northwest. now we go to the surface, and the winds there are blowing in from the southeast, bringing in sticky, warm, tropical air from the gulf. this change in wind direction from the surface to the higher levels is what we call wind shear . that was extreme yesterday and led to the spinning motion and tornadoes. and last night most of that energy was concentrated in this one super cell that produced the first ef4 in texas since 1994 . there will be some severe weather tonight and friday. we think the bigger show, higher risk will be saturday. look at the red on the forecast map. from south dakota to north texas . we shifted east on sunday to include oklahoma city and des moines . and brian , this as today iowa set a state record for the longest stretch without a tornado. 356 days and counting. we hope it continues, but more than likely we'll have twisters to cover on the weather channel all weekend. and that concern will continue east toward chicago by early next week. brian ?
>> mike seidel , part of our team. they have a busy couple of days ahead. thanks.