Core Core Chases

[Shane Adams]

I just don't see how you forecast cold core tornadoes. I look at archived radars from CC days and there's 12 storms out there in a group and one produces a tornado. How do you know which storm to be on? I'm just real down on CC because the only one that didn't do tornadoes was the one I commited to last year and chased in Nebraska. Every other one (that I missed or sat out) goes bonkers. Doesn't matter how many I miss though, I cannot get excited about 60s/50s or even 50s/40s. It's just not natural. However if it looks like a CC setup I'll try, since that looks to be the only shot we have this year within a few hundred miles of home.

MOD (Jeff): As a moderator note, I split this topic off from the original thread since it wasn't really about the upcoming event in particular. This is NOT a bad thing, since I think there is a LOT of interest in these types of events among chasers, and I think this discussion can be greatly beneficial for many. [/moderator]

 

[Scott Currens]

I just don't see how you forecast cold core tornadoes. I look at archived radars from CC days and there's 12 storms out there in a group and one produces a tornado. How do you know which storm to be on? I'm just real down on CC because the only one that didn't do tornadoes was the one I commited to last year and chased in Nebraska. Every other one (that I missed or sat out) goes bonkers. Doesn't matter how many I miss though, I cannot get excited about 60s/50s or even 50s/40s. It's just not natural. However if it looks like a CC setup I'll try, since that looks to be the only shot we have this year within a few hundred miles of home.
[/b]

The reason only one of the 12 storms produce a tornado is, there is usually only one chaser out on a cold-core setup (this is changing) and that was the storm he/she was on. I'm convinced that the only time cold-core setups don't produce tornadoes, is when no one chases them. It's like the tree falling in the woods thing.

The hardest thing about chasing a cold-core setup is realizing that CAPE and LIs don’t tell you Jack about the real instability. All I can say is that -22 at 500mb atop 57/53 at the surface is real instability. I promise you, it is really instability. If you have to, give it a “relative CAPEâ€￾ value of 2000. LOL!

How do I pick my target on a cold-core setup? The easy answer is that I target just east of the warmfront surface low intersection. I like to be close to the surface low, under the coldest 500mb temps (max relative instability) and strong vorticity advection. The 0-1 km shear is usually maximized along the warmfront or a pseudo-warmfront, although the SPC MESO Analysis often does a poor job of depicting this for some reason. I just look at the surface observations and compare them to 850mb RUC analysis. Also, I have noticed that 500mb winds don’t seem to be that important for LT supercells. I look at surface to 700mb for deep layer shear.

Finding your target couldn’t be easier. Just go to the triple-point! Storms usually initiate on the dryline/dryslot move north to the warmfront and produce tornadoes.

LT supercells often appear as clusters or lines on radar, but the updrafts are small and they don’t need that much room to prosper. Using an 88D to observe TL supercells is similar to using XM WXWorx on a classic supercell. The resolution is just to poor to get any real understanding of the cells structure. This is why many people that don't chase cold-core setups label the tornadoes as "landspouts". While I don't see any reason why "landspouts" cannot occur in cold-core setups, I have yet to see one. Each cold-core tornado I have observed has formed within the mesocyclone of a LT supercell.

Would you have given up on the dryline, if your first dryline chase was a bust?

Scott Currens
www.violentplains.com

 

[Bobby Prentice]

I just don't see how you forecast cold core tornadoes. I look at archived radars from CC days and there's 12 storms out there in a group and one produces a tornado. How do you know which storm to be on? I'm just real down on CC because the only one that didn't do tornadoes was the one I commited to last year and chased in Nebraska. Every other one (that I missed or sat out) goes bonkers. Doesn't matter how many I miss though, I cannot get excited about 60s/50s or even 50s/40s. It's just not natural. However if it looks like a CC setup I'll try, since that looks to be the only shot we have this year within a few hundred miles of home.
[/b]

Jon Davies maintains a great web page on this subject at:

Ingredients supporting tornado events associated with closed 500 mb cold core lows

 

[Shane Adams]

Would you have given up on the dryline, if your first dryline chase was a bust?


www.violentplains.com
[/b]

No, because it was and I didn't :lol:

I have no plans to ignore CC setups, I'm just trying to figure out how to do it. Your post helped a lot, which I appreciate. I'm just not used to chasing these type of systems, only having one under my belt (4-11-05). It produced a great supercell (with cold north inflow winds to 40mph while the storm moved NNW) but no tornadoes. It was relatively easy but weird. I guess I just need to get over the mindjob of the surface conditions and concentrate on shear and intiation points, then let Nature worry about the rest. I will definitely be chasing this next system regardless of its nature, I'm just ready to get that first 2006 tornado out of the way!!!

 

[Jeff Snyder]

Shane,

I know what you mean re: hesitation in chasing in 40 Tds. Last year, I missed every cold-core setup, because I couldn't turn away from the highly-sheared dryline / "warm" sector activity (including Mar 21, Apr 5, and Apr 10, 2006). Unfortunately, moisture was a limiting factor (IMO) all three of those days for the dryline/"warm" sector activity. This past monday, however, I (with Gabe and Justin) decided to try our first cold-core chase, and it paid off. It was very odd filming a tornado while in a heavy jacket, with wind chills probably in the 30s with the gusts. From what I've seen, the forecast may actually be easier for cold-core activity relative to warm-sector convection. Assuming the setup follows something like what Davies outlines (sfc low <=200km from 500mb closed low, occlusion front or pseudo warm front east or southeast from the sfc low, etc), your best bet almost always seems to be to anchor on that front/boundary just east or downstream from the surface low. On Monday, we were worried about the fact that Tds were only in the 40s (which is very much in the "low" category relative to that mentioned in the Davies and Guyer paper), but there was a nice surface boundary with extremely cold 500mb temps (probably compensating some for the low tds). With insolation occurring near and on the cool side of the boundary, very steep low-level lapse rates helped to develop strong 0-3km CAPE.


For anyone wondering about cold-core chasing, I strongly suggest you read the following paper:
Davies, Jonathan M., and J. L. Guyer, 2004: A Preliminary Climatology of Tornado Events with Closed Cold Core 500 mb Lows in the Central and Eastern United States. (22nd SLS Conference)

 

[Bob Schafer]

I was reading some of the case studies, etc., and something occurred to me. (First time for everything...)

There are references to "low-topped supercells". I submit that those aren't supercells at all. They simply don't fit the description of what constitutes a supercell. I decline to provide any links to examples, as I don't want to pick on anyone in particular.

Just a little elbow "nudge" to anyone calling those "supercells"....

Bob

 

[Jeff Snyder]

I was reading some of the case studies, etc., and something occurred to me. (First time for everything...)

There are references to "low-topped supercells". I submit that those aren't supercells at all. They simply don't fit the description of what constitutes a supercell. I decline to provide any links to examples, as I don't want to pick on anyone in particular.

Just a little elbow "nudge" to anyone calling those "supercells"....

Bob [/b]

Bob,

Hmm. There ARE low-topped supercells, but I don't know the particular case you are referring to. October 21 2004 was a nice mini-supercell case in east-central Oklahoma -- the storm had a nice RFD, occassional wall-clouds, and other supercell features. If you saw it on radar, however, you'd probably think it was a little shower, since the dBzs were largely <=45dbz and covered a very small area (though there was rotation extending through a considerable part of the storm). Despite the radar appearance, a visual examination of the storm in the field made it pretty easy to label it a mini-/low-topped supercell. I'm not sure if you are saying that there aren't such things as low-topped supercells, or if you are just referring to a particular chase reports that calls particular storms 'mini-supercells' but probably aren't.... I do think some may be a little to quick in labelling a storm a "supercell" (e.g. any storm with rotation in the lowest BRef tilt, without other supercell features present).

 

[Bob Schafer]

Okay, basically what I'm saying is that I see pics of TCu being called supercells simply because they spawned tornadoes. I don't think they had backshearing anvils, overshooting tops, wallclouds, RFD's, FFD's, flanking lines, inflow bands, pseudo CF's, etc. Not that a supercell must, by definition, possess ALL those characteristics, but isn't the term "supercell" being thrown about a little liberally?

*edit* But then, you suggested that as well.

That's all.

Bob

 

[Jeff Snyder]

Okay, basically what I'm saying is that I see pics of TCu being called supercells simply because they spawned tornadoes. I don't think they had backshearing anvils, overshooting tops, wallclouds, RFD's, FFD's, flanking lines, inflow bands, pseudo CF's, etc. Not that a supercell must, by definition, possess ALL those characteristics, but isn't the term "supercell" being thrown about a little liberally?

*edit* But then, you suggested that as well.

That's all.

Bob [/b]

I agree. There are plenty of nonsupercell tornadoes, so a "storm" that produces a tornado does not make it a supercell (just as, I suppose, a supercell doesn't need to produce a tornado to be a supercell). I think the official definition of a supercell only requires that the updraft be rotating (i.e. there be a mesocyclone), but I'd surmise that most (all?) also have RFDs (though some may be weak or competely rain-filled). As you said, most supercells also have overshoots, backsheared anvils (though fewer seem to have them when anvil-level winds are truely intense -- e.g. 140+kts -- for semi-obvious reasons), rain-free bases, inflow bands (probably not so many with those supercells embedded in squall lines), etc. I do agree that some may tend to jump the gun in calling a storm a supercell.

 

[Greg Stumpf]

A good time to share this old image I made about 10 years ago:

These are all supercells, tornadic at the time of the images, and all shown at the same scale. It comes from this page:

http://www.nssl.noaa.gov/wrd/swat/Cases/950213/case.html

 

[Fred Gossage]

Okay, basically what I'm saying is that I see pics of TCu being called supercells simply because they spawned tornadoes. I don't think they had backshearing anvils, overshooting tops, wallclouds, RFD's, FFD's, flanking lines, inflow bands, pseudo CF's, etc. Not that a supercell must, by definition, possess ALL those characteristics, but isn't the term "supercell" being thrown about a little liberally?

*edit* But then, you suggested that as well.

That's all.

Bob
[/b]

Those are characteristics of classic supercells that you mentioned.....but by definition, a supercell is a thunderstorm with a deep, persistent, rotating updraft.... Not all supercells have overshooting tops, bachsheared anvils, and especially wall clouds.

I will agree to the point that some people are calling towering cumulus supercells sometimes, just because a tornado or two is produced, but the storms like Jeff chased on the 12th....and those referenced in many of the online publications ARE supercells because they are thunderstorms with deep, persistent, rotating updrafts.