[BC] Tornado warnings

[Kirk Harnack]

"Calling" a tornado is often a touchy subject.  Before there was Doppler
radar, the NWS would sometimes call a tornado based solely on a hook-echo
return, but they'd say "confirmed" or "unconfirmed" to clarify their call.

Even with Doppler radar (WSR-88D) used by the NWS, calling a tornado isn't
an exact science.  Here's a fairly recent study...
http://cstar.cestm.albany.edu:7773/Research/Comet99/Paper20aa.htm

Figure 1 of this paper shows increasing level of certainty when gate-to-gate
shear (that's velocity toward the Doppler radar in one cell, adjacent to
velocity away from the Doppler radar in the next cell) vs. the large-scale
rotational velocity of the mesocyclone.

Another, very recent, paper - scheduled to be presented in November at an
AMS Conference on Severe Local Storms, describes uncertainties posed even
when 4 Doppler radars are observing the same storm...
http://ams.confex.com/ams/23SLS/techprogram/paper_115287.htm


Probably the paper that best answers the question before our group is this
one, written by Mark Rose in Nashville's Weather Forecast Office...
http://www.srh.noaa.gov/ssd/techmemo/sr215.htm

Mark describes the call-to-action prerequisites.  Indeed, the 4th one for a
Tornado Warning seems a bit weak...

a. Tornado indicated by radar:

    * A tornado may form at any time. Take cover now! Abandon mobile homes
and vehicles for more substantial shelter. Avoid windows.
    * Radar shows strong signs that a tornado is developing. Take cover now!
    * This storm shows strong rotation and may produce a tornado at any
time. Do not wait. Go to a safe place now! Put as many walls between you and
the outside as possible.
    * Doppler radar indicates a tornado may form at any time. Take cover
now! Abandon mobile homes and vehicles. Move to an interior room or hallway
on the lowest floor away from windows.



... And leaves much interpretation up to the forecaster.  

It's certainly inappropriate for NWS Watch or Warning criteria to be abused
in either direction.  What we don't know is just what indications were seen
on Doppler in NC.  I drove through western NC yesterday; lots of rain and
mean, mean skies.  I saw enough sheared clouds to make me think that the
weather *could* have produced a tornado.


Best,

Kirk Harnack


Kevin Webb wrote:

> 
> Kent,
> 
> You are correct for being confused and this is a problem I see that's 
> gotten worse.  Potential does not equal tornado.
> When I used to do weather on TV we did *not* report a tornado warning 
> until one was sighted by a reliable contact (police, known weather 
> spotter, etc.).  But that was in the 80's.
> We were a bit advanced because we actually -had- weather radar.  
> That's showing my age.
> 
> Now they run a tornado warning if they see the conditions are correct 
> on Doppler radar and *not* necessarily an actual tornado.  Yes you can 
> see the classic "hook" or comma signature of wind shear that's 
> *likely* to turn into a tornado but that doesn't mean it IS a tornado.
> 
> I'd like to see someone do a study of when they run tornado warnings 
> based solely on the radar signature vs. one that's actually touched 
> down.  I'll bet they'll see that it is less than 1 out of 10 times 
> that signature turns into anything at all.  This is way too close to 
> crying wolf and the result is the public turns a blind eye and doesn't 
> take the warning seriously.
> Plus how many more injuries and deaths have occurred because of the 
> "cry wolf" syndrome of late??
> 
> 
> Kevin Webb
> ------------------------------------


Ken Winrich posed:

> 
> During the Ernesto thingy here in North Carolina, the NWS kept sending 
> out tornado WARNINGS, but then said that the potential was there for a 
> tornado.
> Correct me if I am wrong but that sounds like a tornado WATCH.  Not 
> once did they say there was one on the ground.
> In the Midwest when we got a tornado warning, we knew we had one on 
> the ground.  Paint me confused.  Do the different NWS office have 
> different standards?
> 
> Signed,
> 
> Your soggy engineer....