Re: SOOTALK Digest V1 #321 (fwd)

Hi Pete, 

I do not know if this event occurred in 2000, but if so it is probably
related to the COMET Case Study CCS033, (Missouri Isolated Severe Weather
20-22 May, 2000 ).

Nice insight to the storm and its conditions, it sounds like the same
event.

If so, please feel free to access any of the data at:

http://www.joss.ucar.edu/cgi-bin/codiac/projs?COMET_CASE_033

and if any work is being done on this event, any contributions or added
insights to the case study would be greatly appreciated.


Thank you,

-Jeff
____________________________                  _____________________
Jeff Weber                                    address@hidden
Unidata Support                               PH:303-497-8676 
NWS-COMET Case Study Library                  FX:303-497-8690
University Corp for Atmospheric Research      3300 Mitchell Ln
http://www.unidata.ucar.edu/staff/jweber      Boulder,Co 80307-3000
________________________________________      ______________________
> 
> Date: Sat, 26 May 2001 18:47:02 +0000
> From: "Peter Wolf" <address@hidden>
> Subject: anticipating landspouts
> 
> SOOs....
> 
> Had an interesting meeting with researcher Jon Davies last week about a
> tornado event on May 20th in central KS (at least 5 or 6 touchdowns and
> additional funnel reports...in environment with 2500 J/Kg CAPE, but
> helicities less than 80 m2/s2).  I believe he has come upon some
> interesting clues for anticipating these events.  Based on what we have
> found in several multiple-landspout events, the following should be
> looked for:
> 
> 1) Large CAPE (at least 2500 J/Kg, preferrably greater than 3000
> J/Kg)... including substantial positive area in the lowest 3km (e.g.
> 700mb LI's of -3 or lower...I've come up with a volume browser field
> that approximates 700mb LIs).  This seems to be critical w/ regard to
> the "stretching term" that appears to be important for landspouts.
> 
> 2) Storm-relative flow aloft of 15 kts or greater...to redistribute
> precipitation away
> from updraft core.  In weak flow environments, this condition can be met
> through deviant storm motion.
> 
> 3) A well-defined boundary, with surface windfields across the boundary
> producing fairly large values of vorticity (e.g. N or NW wind north of
> boundary, SW wind south of boundary).  This can be plotted from LAPS or
> RUC analysis using Volume Browser (higher resolution plot of vorticity
> of surface wind).
> 
> 4) Deviant storm motion that keeps the storm over the boundary (keeping
> continuous feed of air parcels experiencing vorticity within boundary
> into updraft), Storm motion must also be such as to prevent updraft from
> being cut-off by downdraft. For May 20th event, storm motion was almost
> due south at a speed that kept storm above southward-moving cold front
> and apparently ahead of its cool outflow.
> 
> Conditions #2-#3 are often observed, but less so in combination with
> condition #1, and much less so to have all conditions met. For the
> multiple-landspout events we've observed, all conditions were met (also
> met in Jarrell TX event, though the extreme instability yielded more
> than simply a landspout).
> 
> It appears shear is not a relevant factor for landspouts.  In fact, the
> several events
> reviewed were all low-shear events.  What appears to be important is a
> boundary with airflow across it producing positive vorticity, and for a
> storm to somehow to remain over the boundary.  An isolated landspout can
> occur when a storm briefly encounters a boundary with such a "vorticity"
> condition met (have seen this occur, with landspout occurrence ending
> when storm leaves the boundary...this setup
> usually leads to 1 brief landspout/funnel, not multiple), but
> multiple-landspout events appear to require storm to have continuous
> access to parcels acquiring vorticity in boundary (making condition #4
> quite important).
> 
> I've instructed our forecasters (especially this time of year) to focus
> on the above
> conditions, and be in contact with spotters in the locations where the
> conditions are
> met.  In the past, we've had very little skill anticipating such events
> (clueless why they occurred in weak-flow environment).  The above gives
> us a chance to better anticipate such events, and use our spotters to
> help in the warning process (especially given lack of signatures on
> radar).
> 
> Hope the above is helpful...
> 
> Pete Wolf, SOO
> NWS Wichita KS