Do LP and HP supercells produce violent tornadoes?

Michael Auker

Do LP and HP supercells produce violent tornadoes or are they mainly limited to classic supercells? Any examples or case studies?
 
Michael - Dr. Charles Doswell has published many references to the types and structure of supercells. In general, supercells may be classified by their observable, physical characteristics - some produce less downdraft (LP), some have a classic structure, and some produce heavy downdraft (HP). Keep in mind that these are general classifications, and most supercells are actually a hybrid of more than one of these categories together. Storms can easily evolve or morph from one classification into another depending on the environment they enter into. They can even display characteristics of both LP and HP storms at the same time! I think we make too much of these classifications sometimes. All supercells are fundamentally the same. A supercell thunderstorm is any storm that is supported by a single, strong, rotating updraft. They all produce damaging weather, they are long-lived, they all have a mesocyclone. They can all produce tornadoes ... technically any thunderstorm can produce a tornado in the right environment. Even non-supercell storms produce them. And in the right conditions, all of them are capable of producing violent tornadoes.

Some other helpful links:

Forecasting Supercell Type, by Richard Thompson and Roger Edwards: http://www.stormtrack.org/library/forecast/sctype.htm

Supercells (UNL), http://www.hprcc.unl.edu/nebraska/supercells.html

What Is a Supercell?, http://www.cimms.ou.edu/~doswell/Conferenc.../Supercell.html

Storm Chasing With Safety, Courtesy and Responsibility: http://www.cimms.ou.edu/~doswell/Chasing2.html

Advanced Spotters Field Guide (See pp. 26-27): http://www.crh.noaa.gov/lmk/spotter_refere...field_guide.pdf

Structure and Dynamics of Supercell Thunderstorms: http://www.crh.noaa.gov/lmk/soo/docu/supercell.htm
 
Generally, the most prolific violent tornado producer will be the classic supercell. But that's not to say other types can't. As Mike said, all supercells are capable of producing tornadoes and a supercell may morph from one type into another during their life.
 
I would be interested in reading some case studies about long-track violent tornadoes spawned by HP supercells. Does such information exist?

KR
 
As a chaser, I strongly disagree that all supercells are generally the same, regardless of type. Yes, they all have a single, strong, rotating updraft, but that's where the similarities end. Precip type/amount/dump, tornado placement/visibility, life cycle/cyclic characteristics, favorable environment for development - these are just a few examples of the very different aspects of the different sup types. A lot of chasers won't even chase HP supercells, so that alone is an indication fo just how different these "types" can be.

Although, almost any supercell will at least touch upon each type as it goes through its life cycle; many times classics can give the appearance of an HP when cycling down, as the RFD fills with rain and the overall structure becomes "diffused."
 
just a thought on the HP/LP thing.

It would seem to me that strong and/or long lived tornados get spawned out of either classic or HP sups. LP, while producing at times monster hail, usually don't produce strong tornados. Now, that being said, i wonder if more deadly tornados come from HPs then any others? Since HPs often produce rain wrapped tornados, the chances of people being caught off guard is higher then that of a classic sup or a LP sup. I guess they could also produce more deadly tornados because of the locations they effect, often occuring in more populated areas then LPs, meaning a great chance of loss of life



So, what do you think? i'm i nuts or do i have some good ideas?
 
Supercell type is largely determined by the low-level moisture environment of the storm and coincidentally this tends to effect the ability of each to produce tornadoes. LP's typically occur in the High Plains where low-level moisture is sparse and LCL's and in turn the cloud bases are usually > 1500 meters. This in turn makes it much more difficult for the supercell's circulation to interact with the surface and spawn large long-track tornadoes.

There has been relatively little research done on characterizing the environment for the three types of supercell's since a individual supercell can actually morph between the different types as it changes environment...such as a storm moving from the High Plains of western Kansas into the lower and more moisture laden terrain of central Kansas. There have been some excellent proximity sounding studies done by Thompson/Edwards, Rasmussen and I think Brooks has done one as well. Off the top of my head I can't remember which of the studies determined it, but for significant tornadoes (F2 or greater), Classic supercells actually had lower mixed layer LCL's than HP's which from a thermodynamic standpoint is a mystery to explain. As the datasets get larger and model soundings improve we will be able to know much more about the inflow environment and its effects upon supercell type and tornado production.
 
There is a nice web site with forecast parameters for cell type by Roger Edwards:

http://www.stormeyes.org/tornado/stmtype.htm

As for tornado production - I'm not familiar with a LP supercell case producing a violent tornado - in fact they often will not produce tornadoes - but can and occasionally do. Violent tornado cases with CL and HP are fairly common - mostly the former are well documented as classic supercells are more common in tornado alley.

Glen
 
Supercell type is largely determined by the low-level moisture environment of the storm and coincidentally this tends to effect the ability of each to produce tornadoes. LP's typically occur in the High Plains where low-level moisture is sparse and LCL's and in turn the cloud bases are usually > 1500 meters. This in turn makes it much more difficult for the supercell's circulation to interact with the surface and spawn large long-track tornadoes.

I might say that what's just as if not even more important than low-level moisture content when forecasting (or trying to) supercell type is upper-level winds, storm speed, storm motion and all the vectors associated therein when storm motion and speed is vectored against the hodograph's winds at all levels.

A good example of this may be on May 29th 2004, if you recall. The upper winds seemed to be stronger in s-central Kansas and north-central Oklahoma than they were in central Oklahoma and west-central Oklahoma. What did we end up with? A tornadic HP supercell near OKC, and a tornadic Classic supercell up by Conway Springs, Kansas.

If anybody knows of a good case study for May 29th 2004 online - I'd sure love to hear of it (amd I'm sure the beginner of this thread would, too!).

KR
 
I consider it HIGHLY unlikely that an LP supercell would produce a violent tornado. HP supercells can, and do produce violent tornados though. A perefect example of this would be the Plainfield, Illonois torndo of August 28, 1990 that killed 29 people. Another HP supercell that produced violent tornados was the NC Kansas supercell of June 15, 1992.
 
A good example of this may be on May 29th 2004, if you recall. The upper winds seemed to be stronger in s-central Kansas and north-central Oklahoma than they were in central Oklahoma and west-central Oklahoma. What did we end up with? A tornadic HP supercell near OKC, and a tornadic Classic supercell up by Conway Springs, Kansas.

KR

Karen,
Actually, the mid-upper level winds were stronger over OK. The jet streak axis was centered right over centerl OK. For example, at 300mb, DDC had 65kts, while OUN sounding had 90kts... At 500mb, OUN may have been a shade stronger with 45kts, compared to likely the low 40s in souther KS.

See the 500mb, 300mb, and 250mb graphics at http://www.spc.noaa.gov/exper/archive/even...0529/index.html

For this particular event, I still haven't really figured out why the central OK storm was as HP as supercells get, while the southern KS storm was classic. My only observation was that there was stronger/more CINH down in central OK (see OUN sounding) than was the case in southern KS.
 
As a chaser, I strongly disagree that all supercells are generally the same, regardless of type."

I should clarify the statement to stress the word 'fundamentally' in that sentence ... I was actually intending to distinguish supercells from other types of thunderstorms, including clusters and linear events. At the most basic level, supercells have a single rotating updraft and produce severe weather, which is what makes all of them variations of supercells - but I agree that the varieties (LP, classic, HP and mini) are FAR different from a chasing perspective. Would take a classic over HP any day of the week! - Due to our geographic location and the factors already mentioned (moisture, etc) where I live by far the majority of supes around here are HP, so I'm forced to punch rain curtains every year at some point. Also, we often DO have embedded HP supercells within clusters/lines - which is just one more frustration for chasers - that is personally my least favorite scenario as there seems to be downdraft everywhere. In thinking about this I'm not aware of an LP storm producing any long-lived tornado that might be considered 'violent' ... but won't push it completely out of the realm of possibility, of course - since they can and do produce tornadoes and can easily move into an environment where the storm becomes classicly defined and then produce a violent tornado. I feel like some of the judgment made in defining these storms is a bit on the subjective side, though - as every storm is different and they frequently have characteristics of more than one type.

Photos of tornadoes spawned by LP cells can be found:

http://ww2010.atmos.uiuc.edu/guides/mtr/sv.../gifs/home1.gif (Photo credit: Marshall)

http://ww2010.atmos.uiuc.edu/guides/mtr/sv...lp/gifs/ex2.gif (Photo credit: Moller)

These examples are really rare, though - and usually in a storm bordering between what might be considered LP and classic.
 
Photos of tornadoes spawned by LP cells can be found:

http://ww2010.atmos.uiuc.edu/guides/mtr/sv.../gifs/home1.gif (Photo credit: Marshall)

http://ww2010.atmos.uiuc.edu/guides/mtr/sv...lp/gifs/ex2.gif (Photo credit: Moller)
There isn't enough evidence in Marshall's picture to conclde supercell type. He was too close to the tornado.

As for Moller's picture, that is clearly a classic supercell. I can see the wrapping precip. In fact, I wuold go as far as saying that this storm might be more on the wet side of classic, seeing all the precip falling in the rear flank.
 
These images were originally pulled from this U. of IL site, which contains a bit more description if it helps:

http://ww2010.atmos.uiuc.edu/(Gl)/guides/m.../spr/lp/ex.rxml

In looking at the link to Tim Marshall's photo, though - it's difficult to tell if this is another example of the same storm discussed on the primary page or merely an example of a tornado - it's a bit misleading that way - - - got me wondering now.

Sam Barricklow also has some nice examples of storms that move between classifications on his site worth taking a look at here: http://www.k5kj.net/wall.htm (he nicely describes the primary observable differences between supercell types on bottom of this page) ... this particular storm is pretty interesting: http://www.k5kj.net/950605V.htm
 
Tom Grazulis's 2001 booklet F5/F6 Tornadoes notes that "HP supercells are NOT the ones that produce F5 tornadoes. Too much rain is not good for the updraft."

Obviously this isn't a case of HP supercells not producing F5 tornadoes, period — the 1990 Plainfield, IL, tornado shows that — and this comment was in regard to global warming increasing the incidence of violent tornadoes (that there could be an increase in moisture in the air, thus more HPs . . . alternately, he says, it could just as soon be hot but dry and so nary a supercell).

At any rate, the Plainfield tornado was not all that long-lived: its path was 16 miles long. And while it was the last of a family of about 4 tornadoes, the others weren't very long-lived (or violent) either. So, as Karen alluded earlier, it may be that because of its less stable updraft, an HP can produce violent tornades without sustaining them.

It is possible that the 1925 Tri-State tornado was spawned by an HP, but the only real evidence is that no-one could really see a tornado — that's pretty shaky evidence. THis lack of visibility may have had more to do with the size of the tornado (i.e. it wasn't a "classic" funnel or anything) or intervening microbursts.
 
Karen,
Actually, the mid-upper level winds were stronger over OK. The jet streak axis was centered right over centerl OK. For example, at 300mb, DDC had 65kts, while OUN sounding had 90kts... At 500mb, OUN may have been a shade stronger with 45kts, compared to likely the low 40s in souther KS.

See the 500mb, 300mb, and 250mb graphics at http://www.spc.noaa.gov/exper/archive/even...0529/index.html

For this particular event, I still haven't really figured out why the central OK storm was as HP as supercells get, while the southern KS storm was classic. My only observation was that there was stronger/more CINH down in central OK (see OUN sounding) than was the case in southern KS.

Jeff -

You got me going, so I've been digging around for data from May 29th. I was privy to a private discussion between Louis Wicker and others who came to the near-solid conclusion that the northern Oklahoma/southern Kansas conditions were much more favourable than central Oklahoma that day - mainly in CAPE but also in wind fields.

Trouble is - your link above shows the 0Z May 30th OUN sounding, but not the special sounding released from LMN (Lamont) that date at that time (there WAS one - that's why others managed to come to the conclusion of why the southern-KS storm was Classic and the OKC storm was horridly HP).

As soon as I find the LMN sounding - I will post it here, along with perhaps a few of the conclusions of the aforementioned discussion.

I saw Greg Stumpf raise his head in this thread. Greg - care to digress on the May 29th differences????

KR
 
IMO the windfieilds in S Kansas were almost perfect for classic mode. Great directional and speed shear combo, plus the added bonus of awesome vent winds - which is what I based my target decision on. The windfields were equally good in W OK that day for sups too, but the convective temp was 91 degrees - with upper 60s/low 70s dews, I was afraid any storm that could break through would be extremely high-based (20+ spreads are iffy). When we left Norman for N OK that day, I would've bet the farm nothing would go south of Enid, OK. I was wrong about my OK forecast, but fortunately I was right for my KS one.

Main thing I remember about forecasting that morning was automatically shunning N Kansas/SE Nebraska due to weaker mid-level winds; I feared a slopfest was in short order once initiation got underway up there.
 
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