7/3/07 DISC: AL

[Blake Michaleski]

Mobile, AL -

Initial reports were of a tornado. The NWS quickly said it was likely a microburst to which I agreed. Conditions were not favorable for tornadoes but were for pulse type downbursts.

Then some public photos were posted on the local NBC affiliate website in which one photo whows a very smooth funnel touching down. Apparently just a brief touchdown that damaged the local WalMart Supercenter.

I put most of the available info on my blog.

http://convectivetrends.net

With all of the mesoscale boundaries floating around from outflow and sea/bay breeze, its quite likely this was the result of local scale storm environment modification by the boundaries.


edit: geeze... local TV met is calling it a gustnado based solely on the fact that it was a shallow circulation...based on the photo, its a tornado.

 

[John Farley]

Tornado, gustnado, funnel cloud issues today

A SHORT LIVED...GUSTNADO (A VERY WEAK TORNADO ALONG A GUST FRONT)
WITH A RATING OF EF0 (WINDS ESTIMATED LESS 55 MPH) DEVELOPED ALONG
THE LEADING EDGE OF THE OUTFLOW BOUNDARY NEAR THE DAUPHIN WAY BAPTIST
CHURCH JUST ON THE WEST SIDE OF INTERSTATE-65. MINOR TREE DAMAGE
OCCURRED ALONG DAUPHIN STREET NEAR THE CHURCH AND ONE CAR WAS BRIEFLY
LIFTED OFF THE ROADWAY AND DAMAGED WHEN IT WAS BLOWN INTO A TREE. THE
OCCUPANT OF THE CAR WAS WEARING A SEATBELT AND WAS UNINJURED...BUT
THE BACK WINDOW OF THE CAR WAS SHATTERED AND SOME BODY DAMAGE TO THE
VEHICLE OCCURRED. IN ADDITION...A 5 BY 8 FOOT SECTION OF ROOFING
MATERIAL WAS BLOWN OFF THE DAUPHIN WAY BAPTIST CHURCH...RESULTING IN
WATER DAMAGE TO THE CHURCH'S INTERIOR. THE TORNADO QUICKLY DISSIPATED
AFTER THE BRIEF TOUCHDOWN.

The above is from a Public Information Statement issued by the Mobile NWS office. Interesting. Per my understanding of the definitions - and they have certainly been discussed extensively on this board - a gustnado is not a tornado. Now granted that sometimes the line between the two is blurry, but to say that a gustnado is "a very weak tornado along a gust front" certainly does not fit the definitions I have seen of tornadoes and gustnadoes. And parenthetically, if it was "very weak" it seems unlikely that it would be able to lift a car, given what I have seen of wind-tunnel and site survey research on what it takes to lift a car.

Then, if the above is not enough, the PNS goes on to state:

THE OUTFLOW BOUNDARY THAT CAUSED THE DAMAGE AT I-65 MOVED TO THE
SOUTHEAST WHERE SEVERAL PEOPLE SAW A FUNNEL CLOUD NEAR HIGHWAY 90 AND
THE LOOP. THE ONLY DAMAGE THAT COULD BE FOUND IN THIS AREA WAS A TREE
TOP BLOWN OUT AND SEVERAL TRANSFORMERS WERE BLOWN.

Really? My understanding is that if there is a condensation funnel and damage occurs on the ground, it is a tornado, yet this incident, which occured some distance downstream from the "gustnado" and also downstream from the Walmart damage, which was attributed to downburst wind, is described only as associated with a "funnel cloud."

I am not trying to be critical, but when you see this, is it really any wonder that there is confusion among the public and the media about tornadoes, gustnadoes, and funnel clouds?

 

[Blake Michaleski]

I agree, it was either a tornado OR a gustnado...not both.

If you look at the photos, to me it appears to be a tornado. the circulation was not deep enough apparently to be detected on radar which is only a few miles to the west. I think this was possibly a case of pre-existing vertical velocity along a convergent boundary that became stretched by thunderstorm updrafts as described in Caruso and Davies 2005.

http://www.nwas.org/ej/cardav/

I know a few folks at MOB and I'll see if I can find out more.