Rotating Wall Clouds Reports & TOR's

[nickgrillo]

I'm not sure why... but why do some offices issue tornado warnings based upon the report of a rotating wall cloud by a spotter/chaser and others don't? Especially Detroit/Pontiac... I've reported numerous rotating wall clouds when there was only a SVR out and they never upgraded it.

I know the Denver NWS has issued quite a few warnings with the warning saying something like "TRAINED WEATHER SPOTTERS REPORTED A ROTATING WALL CLOUD CAPABLE OF PRODUCING A TORNADO OVER...", etc.

Is there a particuler reason why some offices choose not to issue a TOR when a rotating wall cloud has been spotted? Of course, not all WC's end up producing a tornado, but there is enough risk to issue a TOR!

Can anybody help me out?

..Nick..

 

[David Drummond]

I'm not sure why... but why do some offices issue tornado warnings based upon the report of a rotating wall cloud by a spotter/chaser and others don't? Especially Detroit/Pontiac... I've reported numerous rotating wall clouds when there was only a SVR out and they never upgraded it.

I know the Denver NWS has issued quite a few warnings with the warning saying something like "TRAINED WEATHER SPOTTERS REPORTED A ROTATING WALL CLOUD CAPABLE OF PRODUCING A TORNADO OVER...", etc.

Is there a particuler reason why some offices choose not to issue a TOR when a rotating wall cloud has been spotted? Of course, not all WC's end up producing a tornado, but there is enough risk to issue a TOR!

Can anybody help me out?

..Nick..

Perhaps they couldn't correlate the report with other facts? Such as rotation near that location on radar, other reports etc.

 

[rdale]

Rotating wall clouds in high-based thunderstorms are not going to touch down... Just because you have rotation in a storm does not mean you're getting a tornado - I'm guessing that the other examples you posted had more going on behind the scenes (info you'd never put in a public warning.)

- Rob

 

[Kevin Scharfenberg]

In almost every case, I would guess the WC report is only one part of the decision to issue a tornado warning. Other factors for the warning would usually include radar, the storm's environment, other spotter reports, the storm's history, and so on. Just because the warning states a rotating WC was reported doesn't mean it was the only factor in the decision to issue a warning. The reason the wording of the warning states that a "rotating WC was reported" is because this generally evokes more response from the public than "radar indicated...". If people know rotation has been spotted they are more likely to take the situation seriously than if the warning is just based on radar.

 

[rdale]

"No tornado warning?"

Many factors at play... 1) How strong was the rotation on radar? 2) What was the cloud height? 3) Any history of tornado? 4) What's the met on duty's severe weather knowledge?

Since no tornado touched down - I'd say that no TOR was a good call...

- Rob

 

[Kevin Scharfenberg]

Also the environment is very important. There can be strong turbulent motion, rotation, a visible RFD, strong shear on radar, but the storm may be riding above a shallow cold pool. ALL of this stuff has to go into the warning/no warning decision.

 

[David Drummond]

Rotating wall clouds in high-based thunderstorms are not going to touch down... Just because you have rotation in a storm does not mean you're getting a tornado - I'm guessing that the other examples you posted had more going on behind the scenes (info you'd never put in a public warning.)

- Rob

I wouldn't go that far Rob. I have witness brief touchdowns from higher based storms with rotation. Granted, it's not usually likely, but it does happen.

 

[rdale]

Sorry - referring to high based as in "over cold air below" which we get here in MI much more often that a true "out West" high storm ;>

- Rob

 

[rdale]

I wouldn't say "common" but sure that's a good spot...

 

[Jeremy Lemanski]

if the NWS were to issure warnings based upon only spotter/police/etc. obs. of a rotating wall cloud/funnel cloud/etc. There would be a ton of warnings which would be unwarrented. We all know that some people can't tell the difference between a scud and a funnel. The NWS knows this too. If there is nothing on radar showing any evidence of rotation then chances are they won't issue the warning based only on a person's report. Yes, sometimes there is a touchdown without rotation on radar, but those are small in number compared to the number of reports of rotation that come in that are incorrect.

I hope i didn't confuse you all too much, i think i did that to meself.

 

[Tony Laubach]

NWS in Denver tends to issue tornado warnings for such events when populated areas along the Front Range are beneath this area of circulation.

Several times this year (notably June 10), tornado warnings were issued for the Denver Metro area and/or surrounding urban areas (Castle Rock, Colorado Springs, Greeley) with the wording of rotating wall clouds. I imagine this is done to give heads up the public of the storm, as these storms (especially around here) tend to be massive hailers (again, see June 10). Hail is a big problem around here, and tornado-warned storms typically have massive hail (2in or bigger) associated with them. Now I'm not saying that they issue tornado warnings for hail, but because of the obvious rotation associated with them, they figure it to be a safer bet to issue the tornado warning just in case, as weak tornadoes like to touch down at will around here in the summer. That and SVR-warned storms aren't a big deal around here.

Just a safer bet, I guess... as for other areas, not sure what they're reasoning is, but this is just mine. BTW, I'm typically one of those trainer weather spotters sitting beneath it! :lol: Obviously there are other factors that go into such things. Radar images, storm history, etc (many mentioned in above posts), so visually confirmation of a rotating storm over a heavily populated area would warrent such a warning, I would guess, especially with storms up here!

 

[Andrew Pritchard]

I had an incident I was quite surprised by happen here in central Illinois during the October 29 2004 event. Got on a nice LP supercell, which put out a rapidly rotating wall cloud...which even put down two funnel clouds, each lasting a couple minutes. Scott Kampas, who was nowcasting for me also called me to alert me that the supercell now had a very tight low level couplet, and that it may produce a tornado any minute. The sirens began sounding in the nearby town, so I called the Lincoln, IL NWS office to alert them of the situation (there was only a Severe Thunderstorm Warning out) I let them know, that a wall cloud had been rotating strongly for 15 minutes or so, and had produced several funnel clouds, as well as the strong couplet which Im sure they had to have seen on radar, and they said they were on the situation. They did not issue a tornado warning for another hour, as the storm began weakening.

Wall cloud visible on left side of precip shaft...
[Broken External Image]:http://www.geocities.com/ilxwx/10290404.jpg


Funnel cloud now on the left side of the wall cloud.
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[Broken External Image]:http://www.geocities.com/ilxwx/ILX_SRV_2342Z-BMI2.jpg

[/img]

 

[Doug Lee]

As to why no TOR comes out for rotating wall clouds, I can think of two or three factors that apply.

In spotter training, we are always told to watch for persistent rotation. If one report comes in of a rotating wall cloud, and then no more reports of rotation come in within 5 - 10 minutes, the mets may assume the rotation was not persistent.

Another factor would be the lack of a TVS indcator on the radar system.

Also, the mets that work for several years in the same office tend to become familiar with the patterns and typical behavior of storms in their area. Experience, intstinct, or intuition is hard to quantify or explain, but it is sometimes the strongest and/or the most reliable factor in the decision process.

 

[Andy Wehrle]

I recall something like this on May 23, 2004. The NWSFO in Milwaukee/Sullivan, WI issued a severe weather statement about a storm approaching me, saying that a spotter had reported a funnel cloud near Belleville, but the storm still only had a SVR on it, and a TOR wasn't issued until nearly half an hour later when it had already passed overhead dropping 3/4" hail.

The one brief tornado touchdown it produced developed just a couple minutes after the TOR came out over NWR. I may have caught a glimpse of it, but am not sure: http://www.stormtrack.org/forum/viewtopic.php?t=4872

 

[rdale]

" If you report a wall cloud in an area where the radar is showing NIL rotation they will probably cross check it with other spotters in the area or send a sheriff's deputy out to check it out."

They certainly would ask the hams to have others check it out, but they clearly do _not_ dispatch police officers...