Take a Cold Core Shower

Computer models have been hinting at the return of SW flow over the plains, and a relatively deep, negatively-tilted trough taking shape later during the coming week. Looks like the Wed-Thu time frame this week is shaping up for possible severe, possibly starting in western Oklahoma in Wednesday and hitting eastern Kansas and Missouri by Thursday. The 500mb low looks to be cut off at this point, as well, which may lend itself to yet another cold core scenario. A few chasers in Oklahoma were treated to cold core tornadoes this past Monday.

Cold core environment tornadoes are not quickly noticed by the majority of chasers, though more and more have been noticing them everyday. I started paying attention back in 2001, and have been listening to what Jon Davies says on the subject everytime he opens his mouth. The most intriguing part of the scenario is the fact that the environment closest to the triple point is generally quite cool and relatively dry, so most of the folks living in the path of the low likely wake up and go through their day never giving a thought to the possibility that tornadoes may in fact be in store for them later on.

Basically, what happens is - in an extremely narrow corridor pulling ahead of the triple point, moisture and instability pull in very close to the TP ... it always seems to trigger within 200 statute miles of the triple point - so for a chaser interested in catching a cold core tornado, all you have to do is hug the TP ... can't get any more simple than that! ... What is so deceptive is the fact that instability on cold core days looks cruddy by most severe weather standards. In fact, it looks downright impossible. Generally the CAPE numbers are <1000 J/kg ... and surface TDs are in the low to mid 50s. Yeah, sounds like a typical spring day, right? ... Wrong ... Here is the map for a typical cold core setup. Notice the cold air at 500mb (-16 to -22C), the dry punch moving in from the southwest, and the narrow window of opportunity for the development of severe thunderstorms close to the triple point. I haven't heard Jon mention this, but as a personal observation, it seems to me that most storms in this particular location on days with closed lows, are moving along with the swing of the warm front, so they generally move more north than northeast, the closer they are to the low pressure. But I've seen cold storms move northeast too, so this isn't a hard rule or anything. Just an observation.

Scott Currens has recently been having some nice success since his move to northern Kansas in chasing these particular setups, and has made some good observations about them in this thread in ST. If I wasn't working so much, I would be chasing them too. We'll see how this week stacks up.

(By the way, if you haven't done it yet, be sure to check out the link on Steve Miller's blog concerning Rob Hedrick's very cool, live TV tornado intercept. Terrific video there.)