What lead to the second siren going off finally. He pulled up next to a cop on the north side of the city, yelling to get the sirens going. Storm chaser Jeff Piotrowski's actions helped get that second siren going.

So while it had a 17 minute lead on the actual warning from the National Weather Service, it was a negative 4 minute siren activation. 5:34 the tornado first touches down(17 minute lead time on warning). Tornado warning, now for the Joplin storm, the south one that produces the Joplin tornado. 5:11: 3 minute sirens activated for that. Here is the breakdown of warnings and sirens.ДҐ:09: First tornado warning for the north side of the city. Was your more typical nothing happens tornado warning. There was a tornado warning out for the north side of the city before the Joplin storm, for the storm before it that first gained strong rotation and a big hook. So many ways to end up in the wrong location There's nothing more frightening out there to come across I don't think. So extremely violent and in such an amazingly short period of time. It's just that the storm forms so so close to the safety of all the cold outflow already generated and that it also becomes It is really scary to realize this evolution is possible. Two of them in particular grow and rotate extremely rapidly. But a couple storms pop up immediately ahead of the complex, taping into very unstable air still available there and also the better surface winds that are

It had pretty quickly grown into a cold outflow mess, with an extremely So the early stuff in Kansas continues for a couple hours, doing little more than some mild hail reports. Just the orientation of the stuff popping off in Arkansas suggests to me effects of that outflow boundary are arcing up near Joplin, likely south a bit. On this wide view of the radar you can see the boundary in Arkansas popping off storms as well as theДry line in the plains and the gravity wave across central Missouri Then in nearly the same area you get a storm that pops up just ahead of it(but later on and more east in better low level orientation and flow) and that storm

The old storm in southeast Kansas had been going for hours and did really The storm popping up later and to the east in the better environment, made a massive difference. It's much more clear on radar but figured I should point it out on here. Note that what moves over Joplin isn't a continuation of the convection in southeast Kansas but new storms marked by those new overshooting tops that pop up right before moving

What is for sure is that just ahead of the dry line early, the winds were veered southwest, but that to the east, if they weren't already south, they soon would be. I'd say there are some effects of that boundary back Just west of them it appears that 'line' curves and points northwest towards the northeast corner of Oklahoma. If you watch real close where the Arkansas storms are firing, you can see them doing so on the same sort of line. Here is a closer in look with Joplin marked with the box. Your browser does not support the video tag.

Joplin weather radar