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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!"

November 2, 2006

Chase Acct: October 26 (Southwest KS) [part 1, "The Forecast"]

Filed under: Chase Accounts,Oct 26, 2006,Special Cases,Storm Chasing — Mike U @ 2:36 am

Given the uniqueness of this tornado event, I am breaking this chase account into two parts, the forecast and then the chase itself, for the purpose of documenting all the decision making processes that went on leading to the success of this chase.  I will begin by stating that, yes, my geographical starting location (Dodge City) played a huge role in my decision to chase…being only 30 miles from the target area.  I was working a 9pm to 5am shift earlier that morning, preparing the Southwest Kansas forecast for the time period Oct 26-27th… so I had a very clear idea of the overall synoptic scale situation impacting my forecast area.  For brevity, I will not go into detail on the overall meteorology involved, but I would encourage you to read the Area Forecast Discussion (AFD) I wrote earlier that morning pertaining to the meteorology for October 26th SW Kansas forecast.  You will see me mention things like mid level potential vorticity (PV) and maximized potential instability in the 800-600mb layer at the nose of the mid level dry intrusion.  These are meteorological parameters unfamiliar to many storm chasers and amateur or new severe storms forecasters (mainly because they aren’t available on the internet) — yet are very key factors in many "cold-core" tornado events, I am beginning to find.  While I didn’t mention the possibility of tornadoes in my AFD, I mentioned the key things that seem to be very important for "cold-core" tornado events.  The reason I did not mention tornadoes in my AFD was the simple fact that the surface front appeard to be just too far south of my forecast area, and that any convection in my forecast area would be largely elevated above the shallow stable layer (but just barely).  This was based primarily on the high-resolution NAM model.  Intuition told me, however, that if the front arced back north at the nose of the dry intrusion/PV anomaly into SW Kansas, then insolation could really make things interesting with an enhanced tornado risk. 

At any rate, I got home at 5am and went to bed with absolutely no intention to storm chase, primarily because I had to work again later that evening at 9:00pm, which would restrict me to a very tight leash within an hour or two of Dodge City.  I woke up around 12:30 or so, and the first thing I did when I woke up was check out the weather, since I am always interested in seeing how my forecast is verifying in complicated weather situations like this one.  Much to my surprise, I was seeing the visible satellite image revealing sunshine over the southern counties from Hugoton east to Meade to near Ashland.  We were still in low stratus and drizzle in Dodge City with a northeast wind and 53°F.  See the visible satellite image below, at 1745z (12:45pm CDT):

1km visible satellite image at 1745 UTC on 26 October 2006.  The yellow oval indicates my chase target area after looking at this image and the 17z short-fuse composite.

I then looked at the 17z short-fuse composite and noticed a large surface moisture convergence bullseye over far southwest Kansas near the edge of the clearing on the visible satellite (see image below).  Also of important note was that the surface theta-e ridge was nosing westward immediately north of the OK state border south of Dodge City.  So, putting everything together from just these two charts told me everything I needed to know… the front was farther north and we could certainly be looking at more than just "small hail" that I had put in the forecast for this area earlier that morning at work!  To me, it was looking much more like a potentially tornadic situation after looking at just these two bits of information.  With nothing planned that day until I was due in to work again at 9pm that evening, I decided to give this a shot and head due south from Dodge City to investigate this convective environment.  I was seeing some similarities to 10 April 2005... as storms were developing near the Colorado border… and as the day progressed, storms kept "unzipping" southeast at the nose of the mid level dry intrusion.  When this "unzipping" hits the higher low level theta-e, then tornadic storms could be possible given the massive amounts of nearly stationary surface frontogenesis and vertical vorticity…not to mention enhanced horizontal streamwise vorticity (from 0-1km vertical wind shear) for tilting.  I kept re-creating in my mind how this might unfold a-la 10 April 2005.  I had my camera gear pretty much all packed and ready to go, as I usually do for impromptu situations just like this one.  Since I do not shoot video anymore while storm chasing, the only gear I had to assemble was my photography pack and my laptop computer for GPS navigation.  I didn’t even have my Alltel mobile internet setup going, since I can’t use it (my new Dell laptop does not have a PC card slot, but an ExpressCard slot, so I have to buy a USB adapter)… something I was going to address in the off-season.  I left Dodge City for the drive south around 1:45pm or so.  Chase account to be continued on next blog post…

The short-fuse composite (chart #1) that we are generating every hour at NWS-DDC.  The valid time of this chart is 17z on 26 October, which coincides pretty closely with the visible satellite image above.  Note the theta-e ridge nosing westward towards the maximum area of surface convergence.

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