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A classic mid latitude cyclone is moving across Kansas today. This appears to be shaping up to be a setup very similar to work done by Jon Davies regarding tornadoes near the 500mb low/potential vorticity max coincident with the cold-pool aloft. Here is a forecast I posted to a storm chasing forecast discussion group regarding today’s virtual chase target:
WV loop mid-morning shows nice mid level drying working into western KS. You can see the subsidence/lift couplet near the mid level PV max on the water vapor loop pushing east at a fairly healthy clip. I think initiation by 17-18z in an area north of I-70 east of HLC...with the first storm(s) evolving into supercells by 18-19z with first tor report maybe by this time? Looking at the DDC short-fuse composite (weather.gov/ddc/shortfuse/shortfuse.php) a nice persistence moisture flux convergence max betw HLC and HYS with nose of steepening low level lapse rate and theta-E/CAPE working up into this area as well. I'd like to be near Smith Center KS around 18z if I could be out. This event does have components of the cold-core pattern with the 995 sfc low/sfc wind vertical vorticity max positioned very close to the H5 PV max and cold pocket of -20 to -22ish. I guess you could call it a hybrid... maybe somewhat similar to April 10th last year or even March 27th Kinsley KS event in 2004. After 20z, the whole warm sector should light up, but I don't usually like being directly under the H5/3 jet core which should be flying through most of KS today/Nrn OK. So, I'd either stay along the KS/Neb line near the cyclone occlusion or farther south in the southern half of OK. Good luck to all out today, I'm jealous!
With compact mid level lows like this one today, I like targeting the area very close to the mid level potential vorticity max. This is usually marked by the darkest “dry spot” on a water vapor image. This is an area of strong subsidence in a maturing cyclone that contains some air from the stratosphere which contains a lot of “potential vorticity”. Just downwind of this PV max (northeast in a northeasterly moving cyclone) is where the best lower tropospheric “response” will be , where frontogenesis is usually maximized and lift is strongest. When there is potential instability involved (usually diagnosed by CAPE fields or theta-E ridges at the surface) near this area, then this potential instability is released vigorously along with the extra deep lifting from all the other “dynamics” involved. To make a long story short, “low-topped” supercells are favored in these areas. Today, between 18z and 20z, the “sweet spot” for all this appears to be setting up in far north-central KS for these kind of storms. Tornadoes usually occur in this area. So, I’d be favoring strongly the Smith Center to Mankato KS area to Osborne to Beloit around this time if I could chase.
