High Plains Drifter

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April 10, 2009

Thoughts on 9 April 2009 “cold-core” event (or lack thereof!)

Filed under: General Weather & Forecasting — Mike U @ 6:28 pm

My sudden mid-afternoon pessimism regarding the "cold-core" setup across south-central Kansas yesterday was realized.  Storms did develop in the target area as mentioned in the forecast blog posts, but none of them were tornadic based on any reports.  I say "based on any reports", because between 2205 and 2215 UTC (5:05 and 5:15pm), KICT WSR-88D revealed a very interesting, very small scale shear couplet with at least 3 volume scans of temporal continuity.  The 2210 volume scan revealed what I believe is a TVS signature about 6 miles northwest of Goddard.  It was only on one volume scan, and the entire shear signature was gone after 2215 as it evolved very quickly.  Was there a brief tornado here?  That brief TVS was only 11 miles from the KICT radar (with the center of the beam hitting an altitude of only ~ 500 feet above radar level at that range), and since the storm was so close to the KICT radar, the reflectivity looks unorganized and messy at best.  A look from KDDC at that time revealed a 50dbz core extending up to about 20 thousand feet above this area.  That brief TVS was interesting to say the least and is very convincing given temporal and even elevation angle continuity.  Whatever happened, happened fast, probably less than a minute, and since there were no chasers out there that I know of west of Wichita at that time, if an event occurred there, it probably wasn’t observed.  Who knows.  I’m not aware of any damage reports from this location.  See the 3-image composite below:

Storm chaser Dean Cosgrove sent me a couple links to images he captured of a well-defined funnel cloud from one of the storms along the occluded front in northeastern Pratt county near Preston at around 2135 UTC (4:35pm CDT).  Below is one of the images.

Why weren’t storms more productive tornado wise?  This is very difficult to answer with any degree of confidence since I haven’t done an in-depth post analysis of the event yet, however I think that southwesterly dry winds were converging too close to cooler northeasterly winds just to its north.  There wasn’t a wide enough favorable airmass in between the dry southwest winds and cool northeast winds for storms to thrive long enough in order to take advantage of the rich ambient vorticity that was around.  I think storms simply became undercut too quickly by cool northeast winds that resided immediately north of southwesterly surface winds.  There really wasn’t much of a corridor of easterly or southeasterly winds (all that’s needed is about 20 to 40 mile wide corridor based on my experience from 26 October 2006 and 10 November 2008), and on 9 April there wasn’t even that, I don’t think.  Again, I will have to look at the mesoscale data in order to help answer this.  I also think the advancing cold front from the northwest was too much for the surface-based storms as well.  Intense convection simply didn’t last that long.  I also think this event lacked "converging boundaries".  Both on 10 November 2008, and 26 October 2006, it was interesting to see on satellite imagery hours before the event occurred, the presence of cumulus cloud lines marking surface boundaries…which ultimately converged on one another in a constructive manner favoring tornadogenesis.  I don’t think this occurred yesterday from what I saw in the data.  I think this may have to do with the positioning/evolution of the 400mb PV anomaly.  On 10 November and 26 October, the 400mb PV anomalies were very focused and even more mesoscale than yesterday.  Yesterday’s 400mb PV anomaly was broader as it moved east, leading to a much broader surface response in the wind field.  I don’t think the vertical vorticity axis was tightly concentrated over one specific area, but was rather strung out all along the occluded front without much room for storms to take advantage of before becoming overwhelmed by either chilly northwest surface winds or northeast surface winds.  I’m thinking out loud here, but these are my early impressions on yesterday.  These are very mesoscale details that make a huge difference in whether a "cold core" event is productive or not.  This kind of detail can not be forecast with much ease at all.  I more than likely would have busted yesterday had I chased, as I targetted Kingman.  Congrats to Dean Cosgrove for at least intercepting something somewhat interesting from one of these short-lived storms.



  1. Mike, there’s a second “TVS” signature that passes about 1 mile NW of Saint Marks as well. See it?

    Comment by gstumpf — April 10, 2009 @ 9:04 pm

  2. Greg, yep. I noticed that as well, but didn’t think it was quite TVS strength… This is the Bookbinder curve, so those colors correspond to about mid-upper 20s on either side… man, this is an excellent example of the need for phased-array 1-minute or less volumes!

    Comment by Mike U — April 10, 2009 @ 9:13 pm

  3. Thanks Mike,
    Based on what I experienced in the field I think your initial impressions about the surface winds is correct.

    Comment by Dean Cosgrove — April 11, 2009 @ 8:40 am

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