6/16/10 DISC: SD

[Matthew Grzych]

This brings up an interesting point for debate. If you have a multiple vortex tornado that is associated with one parent broad scale circulation and is spitting out subvortices on a regular basis, do you call each subvortex a unique tornado? The answer to this question is no. I wasn't there in Dupree, but from the video and pictures I saw it appears that there were multivortex tendencies with this storm at times. Maybe the report of 16 tornadoes is a bit inflated?

 

[Greg Stumpf]

Oh. OK. Sorry Greg. I guess you don't like my terms. I guess maybe I should have written the 'tornado' 'forms' and 'dissapates'. So so sorry about that. So sorry.

Sheesh.

My reply wasn't intended to be snarky. Hopefully this longer explanation is more satisfactory...

If the vortex completely dissipates and then a new vortex forms, then yes, I would say new tornado.

However, many times, the vortex weakens to below damage-causing winds and then re-strengthens above the damage threshold again. That would be one tornado.

A vortex can weaken to a level at which the air pressure within the vortex increases and the resulting condensation vortex appears to "lift". What is actually happening is that the level at which the rising air in the vortex condenses (the LCL or lifted condensation level) increases in altitude, and the "cloud base" of the condensation funnel goes up. Similarly, as the vortex strengthens and the pressure drops again, the LCL of the condensation vortex begins to lower in height and "drop" again. This occurrence is usually what leads people to believe that the tornado is lifting and dropping (or skipping), even though the vortex of wind really does not do that.

 

[Matthew Grzych]

Yes. The wind field was really weak yesterday. That helped to keep the storm anchored on the boundary. Also, once the storm was rooted in the boundary layer, that allowed the storm to slow down even more. Looking at the radar loop, you can see the storm "flying" (relatively) to the North and then come to an almost complete halt once it becomes surface based. Pretty cool to watch it sit there and cycle over and over again.

The SR inflow has nothing to do with the storms movement. The movement is based on the flow in the upper part of the storm.

I'm not sure if you can call yesterday's wind field "really weak". Actually it was just the opposite. Looking at a sounding there was 30-35 kt at 500 mb, 60-70 kt at jet stream level, and there was amazing inflow to the south of the warm front on the order of 30-40 kt of southeasterly surface inflow. For a stationary storm, this storm had quite an amazing wind field and hodograph for tornadoes (not to mention the big CAPE and low LCLs). You just don't get prolific tornado producing storm's with a really weak wind field (like 10 kt or less through the profile). Also a storm's motion is based on the integrated wind vectors from the bottom to the top and whether or not it's updraft convergence and forcing is "anchored" on a boundary like a slow moving warm front... which probably was the case near Dupree.

 

[Bill Hark]

My reply wasn't intended to be snarky. Hopefully this longer explanation is more satisfactory...

If the vortex completely dissipates and then a new vortex forms, then yes, I would say new tornado.

However, many times, the vortex weakens to below damage-causing winds and then re-strengthens above the damage threshold again. That would be one tornado.

A vortex can weaken to a level at which the air pressure within the vortex increases and the resulting condensation vortex appears to "lift". What is actually happening is that the level at which the rising air in the vortex condenses (the LCL or lifted condensation level) increases in altitude, and the "cloud base" of the condensation funnel goes up. Similarly, as the vortex strengthens and the pressure drops again, the LCL of the condensation vortex begins to lower in height and "drop" again. This occurrence is usually what leads people to believe that the tornado is lifting and dropping (or skipping), even though the vortex of wind really does not do that.

Interesting point. This would make counting tornadoes very difficult especially under chase conditions and a rapidly moving storm. I had forgotten about visible and nonvisible circulations. Maybe one can see multiple tornadoes but the final determination would be through damage surveys. How are official tornado numbers on the same storm counted through the NWS?

Bill Hark

 

[Derek Weston]

Since we're getting off topic... never really understood the point of counting tornadoes on a cyclic supercell. (especially when time between is short)

I'd be more interested in counts of tornadoes with different supercells.

 

[Bob Schafer]

I wonder how they handled their sirens, if those things aren't supposed to run long. I could hear them going for quite a long time. They had to be under a tornado warning over an hour straight. I imagine the cops were telling them when to sound them. For a long time all that seemed to be on it were myself, Bob Schafer(I hope you got east) and a couple tours.

That's kind of funny, Mike, because I was wondering that myself today. Imagine being in Dupree, and getting that first TOR. So then, how long did they sit in their shelters, and what did they do after they came out and there were more TOR's? And, crap, we're talking about TOR's for HOURS, man!

NO!!!!!!!!!!!!!! I DID NOT FRICKEN FRACKEN GET EAST! AAAAARRRRGGGHHHH!!!!!! I MISSED ALMOST EVERYTHING!!!

After you left, I knew that the storm to the NW was toast, but nevertheless it looked pretty cool for awhile there, so I embraced the strategy of 1) watching that first storm until it died for good, and 2) letting the "main show" cross the road and then getting back around to the SE of it. I even called RAP to advise them that the NW cell was not producing after they TOR'd it. Except, we all know that the SOB NEVER CROSSED THE ROAD. What you had said kept ringing in my ears: "Will it turn right before or after the road?"

So, I sat just west of the precip for hours on end. Some chasers are willing to core punch. God Bless Ya. I'm not.

At one point, a tornado developed right over me, and I was in the ground circulation for a few seconds until I bailed a couple hundred yards west, LOL. (I called RAP with a report.) I think Andy G was sitting right across the road from me at the time. As I bailed west, he took off towards the core. Credit where credit is due.

Finally, I got fed up with the whole scenario and went back to Faith, where I apparently got the last vacant motel room in town. There was no electricity in town, but at the motel they had a couple cases of beer on ice in the cafe, some flashlights and candles, and about a dozen of us listened to the owner play the guitar and sang along until about midnight while watching the lightning show outside.

Once, the owner's wife saw me unlocking my motel room, and advised me "You don't need to lock your room around here, hon". After that, I didn't.

God, I love chasing.

 

[Andrew Ryan]

I'm not sure if you can call yesterday's wind field "really weak". Actually it was just the opposite. Looking at a sounding there was 30-35 kt at 500 mb, 60-70 kt at jet stream level, and there was amazing inflow to the south of the warm front on the order of 30-40 kt of southeasterly surface inflow. For a stationary storm, this storm had quite an amazing wind field and hodograph for tornadoes (not to mention the big CAPE and low LCLs). You just don't get prolific tornado producing storm's with a really weak wind field (like 10 kt or less through the profile).

Well, I was speaking in relative terms. This was not a highly sheared environment by any means. And, yes, you can have prolific tornado producing storms in a weak wind field, ala Jarrell, TX May 27, 1997. But that's the exception, not the rule. My point was that the wind field was marginal but did allow for downdraft/updraft separation.

Also a storm's motion is based on the integrated wind vectors from the bottom to the top and whether or not it's updraft convergence and forcing is "anchored" on a boundary like a slow moving warm front... which probably was the case near Dupree.

True. But my point is that most of the "steering" comes from the upper level winds. And supercells can deviate from this mean wind.

 

[Greg Stumpf]

This would make counting tornadoes very difficult especially under chase conditions and a rapidly moving storm.

Correct, it isn't always easy in real time, but in any storm, not just rapidly moving storms.

Maybe one can see multiple tornadoes but the final determination would be through damage surveys. How are official tornado numbers on the same storm counted through the NWS?

Even damage surveys don't always reveal the truth, especially in the case of weakening and strengthening vortices, and especially when there is a dearth of "things" to damage. There have been times when I needed storm video to help with damage surveys (e.g., the El Reno OK 4/24/06 tornadoes, which hit very little).

The NWS is supposed to count tornadoes as separate circulations, but that guideline is not always followed due to 1) challenges determining that from surveys as stated above, and 2) the same differences of understanding/knowledge about "what is a tornado" that we see here on ST!