Non-Supercell Tornadoes (Waterspouts/Landspouts)

[Simon Brewer]

I think this is a very important subject, because it could result in a change of forecasting methods not only regarding cold-core cases, but cold-core cases involving an occluded boundary like the one on March 20, 2006 and October 26, 2006 and to a certain extent March 21, 2005 and April 10, 2005. (I’m not a sure about April 10, 2005, because I know many tornadoes occurred in the warm sector, but I think some of the tornadoes further west occurred along an occluded boundary.)

Whether a majority of the tornadoes that occurred in SW Kansas on October 26, 2006 were non-supercell or supercell in origin (a debate involving tornado genesis, dynamics and storm environment data), it’s extremely important to recognize these cases for future setups. It is my opinion there should have been a tornado watch up on September 21, 2006 before a tornado was on the ground in Russell, KS. I think there should have been a tornado watch up on October 26, 2006 in SW Kansas before the first tornado reports went out. I think there should have been a severe thunderstorm watch up in the vicinity of NW Oklahoma on March 20, 2006 before the Putnam, OK tornado touched down. The important thing to remember for all of these events is the lack of CAPE forecasted by all the Forecast Models, and to recognize the setup and the ingredients when they are in place.

If we try to blow off these cases involving cold-core tornadoes along occluded fronts as being unforecastable land-spout events then the public will never receive warning when these events occur. As a result will the public ask why they received little if no warning for tornadoes, while a storm chaser sits down the street documenting the tornadoes?

 

[Dick McGowan]

It is my opinion there should have been a tornado watch up on September 21, 2006 before a tornado was on the ground in Russell, KS.

IIRC, there was a mesoscale discussion up for the area some time between 11 a.m. and 12 p.m. calling for a tornado or two, but a watch was not anticipated. The weather radio even mentioned brief weak tornadoes. I can't recall when the watch was issued though.

 

[afischer]

IIRC, there was a mesoscale discussion up for the area some time between 11 a.m. and 12 p.m. calling for a tornado or two, but a watch was not anticipated. The weather radio even mentioned brief weak tornadoes.

In my opinion, that's exactly where the problem lies in red-boxing these set-ups in advance. In addition to the forecast challenges of anticipating the events themselves (already well-summarized by Scott Currens), I think there's kind of a fine (and tough-to-determine) line between whether a few brief spin-ups will occur or something more significant. How serious will the tornado threat really be, how widespread, and how long will it last? I certainly didn't expect to see two eight-minute duration tornadoes when I left the house the morning of Sept 21... or even after checking data around 1pm.

Just my 2 cents.

 

[Rich Thompson]

I think this is a very important subject, because it could result in a change of forecasting methods not only regarding cold-core cases, but cold-core cases involving an occluded boundary like the one on March 20, 2006 and October 26, 2006 and to a certain extent March 21, 2005 and April 10, 2005. (I’m not a sure about April 10, 2005, because I know many tornadoes occurred in the warm sector, but I think some of the tornadoes further west occurred along an occluded boundary.)

Whether a majority of the tornadoes that occurred in SW Kansas on October 26, 2006 were non-supercell or supercell in origin (a debate involving tornado genesis, dynamics and storm environment data), it’s extremely important to recognize these cases for future setups. It is my opinion there should have been a tornado watch up on September 21, 2006 before a tornado was on the ground in Russell, KS. I think there should have been a tornado watch up on October 26, 2006 in SW Kansas before the first tornado reports went out. I think there should have been a severe thunderstorm watch up in the vicinity of NW Oklahoma on March 20, 2006 before the Putnam, OK tornado touched down. The important thing to remember for all of these events is the lack of CAPE forecasted by all the Forecast Models, and to recognize the setup and the ingredients when they are in place.

If we try to blow off these cases involving cold-core tornadoes along occluded fronts as being unforecastable land-spout events then the public will never receive warning when these events occur. As a result will the public ask why they received little if no warning for tornadoes, while a storm chaser sits down the street documenting the tornadoes?

Simon,

While it's nice to be perfect (i.e., a watch preceding *every* cluster of tornado reports), it's probably not going to happen. You mention "while a storm chaser sits down the street documenting the tornadoes", as if the "chaser" would clearly do better with the majority of "cold core" tornado forecasts. What happens to the chaser when he/she over-forecasts an event? Well, you might waste some of your own time and money, but it adversely impacts nobody but you. That's not the case with SPC outlooks and watches.

Perhaps you should come sit in with an SPC shift just to see what's going on during one of these events. I promise you there's a bunch more to it than simply picking a chase target and heading out the door.

Rich Thompson

 

[scott r currens]

If a distinction is made between supercell and non-supercell tornado then you have to draw a line somewhere.

I said this? I'm not a proponent of drawing distinct lines between mesocyclone and non-mesocyclone tornado processes. As others have already stated, there is a spectrum of processes. Many have noted that some supercell-related tornadoes sometime get a "kick" from some stretching of vertical vorticity while interacting with a boundary (outflow boundary, or an RFD or FFD boundary from the parent supercell). And some seemingly "pure" landspout tornadoes have been observed (by me) to develop clear slots and a mid-level circulation during the muture portions of their lifetimes.

Two big problems with what I posted earlier.

First, when I listed your name I had know first hand knowledge of your opinions on this case, just second hand info from friends that I presume read your thoughts on a different forecasting forum. Greg, that was wrong and I apologize. Jon Davies thoughts on the subject are public and I have discussed CC events with Jim Ladue and he described the March 21, 2005 as "Colorado type landspout event" in the Storms of 2005 DVD, so I do think it is fair for me to express my opinions on what they have said.

Second, my statement was very confusing. I don't think that anyone is trying to say that clear lines exist between supercell and non-supercell tornadoes.

When people say events like this are "landspout tornado outbreaks" "a Colorado type landspout event" or "an event dominated by non-mesocyclone processes", I think they are over simplifying the tornadogenesis process at work and are jumping to conclusions based more on theory than observation.
These events are not the same as your typical Colorado "landspout" event, they involve major cold core low and strong CVA. The individual storms often are small supercells. Some cells that are not supercells by definition still display many supercell characteristics for a short period of time. In the end I just disagree with the notion that miniature supercells have little to do with the tornadogenesis process on this and other cold core events.

As others have said, we really need mobile radar observations if we are going to improve our understanding of cold core events. How much does it cost to rent a DOW during March and April? LOL

 

[Simon Brewer]

Simon,

While it's nice to be perfect (i.e., a watch preceding *every* cluster of tornado reports), it's probably not going to happen. You mention "while a storm chaser sits down the street documenting the tornadoes", as if the "chaser" would clearly do better with the majority of "cold core" tornado forecasts. What happens to the chaser when he/she over-forecasts an event? Well, you might waste some of your own time and money, but it adversely impacts nobody but you. That's not the case with SPC outlooks and watches.

Perhaps you should come sit in with an SPC shift just to see what's going on during one of these events. I promise you there's a bunch more to it than simply picking a chase target and heading out the door.

Rich Thompson

Rich,
I am sorry you have to become so defensive. I hope you are not implying that I don’t know how to forecast just because I am not a paid operational forecaster? I was not intending in any way be offensive or to sneak a jab at the SPC or your job for not throwing up watch boxes before these events. My opinion is still my opinion, but that opinion was generated from my forecasts, and I understand other forecasters may have other opinions thus their own forecast, so I’m sorry if you were offended in any way.

I know this is not a ‘perfect world’ and some events are over forecast and some are missed, but (no offense to the SPC or the forecasters involved) it seems when it comes to cold-core events there are not only more misses than hits, but a complete lack of acknowledgement of the possibility of severe weather. I completely understand before Davies work on cold-core events these events were heavily overlooked by forecasters, but I’m surprised to see these events are still seemingly overlooked. Now, I said seemingly overlooked, because I’m not behind the desk with every forecaster in the world, so I actually don’t know what they are thinking. I am simply trying to emphasize the importance of ‘learning’ from these cold-core events and forecasting future events.

 

[Paul Knightley]

This is an interesting topic to me, largely because many of our tornadoes in the UK may develop from "ordinary" storms rather than supercell storms.

However, one question I feel I must ask is what do people consider to be different about the tornadogenesis within a supercell storm compared to an "ordinary" storm? Both result from the stretching of vertical vorticity. I obviously understand that the vorticity present in either case may be the result of different processes, but I can't help thinking that certain "things" within supercells contribute to tornado-genesis more that others.
For example, the RFD - just suppose an RFD occurred to the read of a "normal" cell - could the resulting vorticity present along its leading edge be tilted/stretched by the nearby updraught into a tornado? If so, does this mean that the updraught characteristics per se are not responsible for the tornado's development? Consider a developing tornado forming underneath a strong mesocyclone - does this tornado become strong because the updraught itself is strong? Does that then mean that the rotation of the updraught only helps tornadogenesis because the updraught is enhanced, and not because it is rotating? I am interested in others' thoughts on these points.

 

[MJ Poore]

Paul, you have a very complicated view of life.

We had a tornado report two weeks ago down here. The radar showed a strong thunderstorm which produced hail, heavy rain and strong winds. But a clue was the fact that the storm happened in a very strong low level shear environment, the wind on the ground, the LLJ, was blowing at 180 degrees backing to the wind at 2000 meters above it. That'll make anything spin, supercell or no supercell.

 

[Paul Knightley]

If you think tornadoes are not complicated John, you must have a highly simplistic view of things!

 

[MJ Poore]

Strong shear, Paul. Strong shear. It's simple or complicated depending on how you look at it. Strong shear can make even the smallest storms do wild things. You with me?

regards
Mungo

(John is my middle name, it keeps things simple online, because sometimes people think Mungo is a nickname etc etc. It's actually an old Scotttish name, but because I live in Africa people think its ethnic or something.)

 

[Paul Knightley]

Strong shear itself does not create tornadoes!

Anyway, back to the main topic of the thread - has anyone got any more thoughts?