[BC] Tornado warnings

[Mike McCarthy]

 From one who spends some time at a NWS office during severe weather...

The NWS's standard for issuing warnings covers a bunch of possible 
scenarios.  We are aware of the usual visual sighting of a funnel or 
tornado (which is defined as where the column of rotating air is in 
contiguous contact with the ground) and advance indications as shown by radar.

One of the criteria for issuing tornado warnings is driven by the WSR88D's 
programming which a defined TVS (tornado vortice signature) on the radar is 
confirmed and monitored for a period of time. This is usually derived from 
the relative storm velocity and a very tight couplet is observed (where the 
incoming versus outgoing velocities go gate to gate in immediately adjacent 
pixels (at distance) or clusters of pixels closer in to the radar.) The 
radar focuses on that segment looking at various elevations to see if the 
rotation is evident at different elevations.  If the rotation is not 
evident higher or lower, the segment continues to be monitored, but the 
warning becomes a gut decision for the forecaster.

Given the extreme number of eddies and micro vortices in the overall 
circulation of the parent storm being within the span of the radar's 
detectable span, it doesn't surprise me a number of TOR's are being 
issued.  Many F-0 wind speed tornadoes form in tropical storms and related 
intensity tornadoes in higher category hurricanes.  But many of them are 
never acknowledged since the damage caused by those micro storms are always 
intermingled or considered as being created with the overall storm.

Thus, what might be a severe wind gust or two...or three could in fact be a 
clear air tornado of similar or slightly higher magnitude air speed than 
the surrounding overall wind field.  But lacks the classically observed 
debris field because the sheering winds present in the overall wind field 
simply creates too much disturbing turbulence to allow the debris field to 
materialize.

MM

At 11:16 PM 8/31/2006 -0400, Kent Winrich wrote
>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....
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