High Plains Drifter

disclaimer:  "The meteorological views/forecast thinking expressed are those solely of the author of this blog
and do not necessarily represent those of official National Weather Service forecast products,
therefore read and enjoy at your own risk and edification!"

March 31, 2006

3/30/06 Virtual Chase Verification

Filed under: Storm Chasing,Virtual Chasing — Mike U @ 10:28 am

entry_20060331_1.jpgWell as any good forecaster should do, I’m here to verify my forecast from yesterday’s virtual chase. My primary northern target to intercept the first supercells of the day in north central KS west of Highway 81 didn’t really pan out. Storms developed in the target area around 17z or so just as I had though, however too many storms developed given the lack of a “cap” and the orientation of the convection was north-south…with prevailing mean shear vectors being of strong southerly component, that did not allow for discrete cells to develop, but rather a messy line of marginally severe cells (see left radar panel below). My southern (secondary) target in southern Oklahoma worked out a little better. A classic supercell developed near Duncan, OK by mid-afternoon which did produce at least one tornado near the town of Velma, according to a few storm chaser accounts.


March 30, 2006

Virtual Chase Target: March 30

Filed under: Chase Forecasts/Outlooks,Storm Chasing,Virtual Chasing — Mike U @ 10:10 am

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.

Mar30 15z Short-fuse Composite #2Mar30 15z Short-fuse Composite #1

WV image (left).. radar (right)

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