10/26/06 DISC: KS

Congrats Mike!! What an AWESOME catch! I was watching the event unfold from on top of Monument Hill, south of Castle Rock, CO. I was watching sat and radar and saw your set up unfold quite nicely, wishing I were there! Instead I was in the middle of a full fledged blizzard with clocked winds to nearly 60 MPH, 14" of snow with drifts to 5 ft and complete whiteout conditions. I like your side of the system better LOL!!

Looking forward to your writeup and photos!

Roger Hill
 
Yeah Mike, damn! And all this time, I was going to pull bragging on you cause you were missing an awesome snowstorm! Guess I'll insert foot into mouth and smile LOL
 
I would be interested in hearing some comments on why these cold core outbreaks are so difficult to forecast. The SPC didn't have a risk for tornadoes or severe thunderstorms in that region. Even in their updates throughout the day I didn't see a risk added.

What makes the cold core outbreaks so difficult to forecast? Are there some good papers to read on this subject?

Did the local offices forecast this event?

This was the third big event in that region (during the past year - I believe) that involved a similiar set-up.
 
What makes the cold core outbreaks so difficult to forecast? Are there some good papers to read on this subject?

There are a couple of relatively recent publications focused on cold-core setups:
Preliminary Climatology of Tornado Events with Closed Cold Core 500mb Lows.(Davies and Guyer)

Guyer, J.L., and J.M. Davies, 2006: Enviroment Characteristics Associated with Tornado Events near Closed Cold Core 500 MB Lows. Preprints, 23nd Conf. Severe Local Storms, St. Louis MO.

I think the biggest problem lies in the fact that the parameters of "cold-core" setups are far from what we've come to expect from tornadic supercell cases. In addition, there's even some debate as to whether these events are nonmesocyclone tornadoes or mesocyclone tornadoes associate with relatively short-lived mini- or low-topped supercells. I'll be presenting a poster at the upcoming SLS Conference that focuses on the 3-20-06 NW OK cold-core tornado, which had dewpoints below the common lower threshold set forth by a previous Guyer and Davies paper (~50F).

From a chasing perspective, I don't think they really are that difficult to forecast. The cold-core setups that seem to produce are those with a surface low <150km from the center of a 500mb low, a distinct pseudo-occludded front, and steep low-level lapse rates that yield some decent low-level CAPE. The boundary involved yesterday was well-developed and clearly evident on local 88Ds. Earlier this year, on 3-20-06, we parked ourselves along a similar, well-defined surface boundary in NW OK, and waited for a moderate convective cell to approach, interact with, and cross the boundary. Well, not entirely unexpectedly, the cell quickly developed substantial rotation, took on supercell characteristics (RFD clear slot, wall-cloud, etc), and produced a tornado; all the while it, was snowing 30-40 miles to the northwest.

The last line of my last post in the FCST thread:
" There may be a risky cold-core play across far nw OK and eastern OK panhandle if the 12z RUC verifies."
This makes my choice even more frustrating, since I looked at the cold-core play (in the mid-morning, it appeared as though the front may stay in OK, which is why I mentioned far nw OK... Obviously, the front ended up in sw KS, so adjustment would have been needed!). So, why did I chase south of ICT yesterday instead of south of DDC yesterday? The same reason why I chased the warm-sector several times during the spring of 2005 while the cold-core play was lighting up to my northwest... It's tough for me to drive hours to a location, hoping to see tornadoes, with temperatures in the 50s and dewpoints even lower, when I can play a more "typical" warm-sector setup (dewpoints in the 60, good veering wind profile resulting in substantial low-level shear, etc). This will change next year, as I've realized that the cold-core target has been remarkably consistent the past 2 years, particularly since many of the cold-core days in the past couple of years have feature warm-sector setups that have had to deal with marginal moisture.

It is very important to determine, however, if yesterday's tornadoes really were associated with low-topped supercells with (relatively) deep, persistent mesocyclones (a little redundant, since supercells, by definition, contain deep, persistent mesocyclones). I haven't looked at radar data from the event, but there's the possibility that these were nonmesocyclone tornadoes caused by intense stretching of ambient vertical vorticity not associated with deep, persistent mesocyclones. This is a very important distinction to make! Many landspout tornadoes on the Front Range are caused by strong low-level vertical acceleration associated with building TCu stretching vertical vorticity in or near a misocyclone. A "cold-core event" typically refers to situations in which convective cells "feed off" the ambient vertical vorticity along a boundary and develop relatively persistent, deep mesocyclones. On the 3-20-06 case, the cell near Putnam indeed did develop a deep, persistent mesocyclone, along with other supercell "features" (RFD clear slot, etc, as noted earlier). I suppose much of this comes down to the depth and duration of the rotation in the cell. Were they really tornadoes associated with supercells / mesocyclones, or were they more shallow, landspout-ish tornadoes? It's not entirely a clear-cut distinction in the first place, and I haven't looked at any radar data to determine either way.

Did the local offices forecast this event?
The only mention by DDC that I read in yesterday afternoon's AFD was this: " VERY LIMITED CAPE SHOULD KEEP STORMS BELOW SEVERE LEVELS."

Did the SPC update their 20z outlook to account for higher tornado probs when they issued the tornado watch for SW KS?
 
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I think there were some of both (mesocyclone and misocyclone) tornadoes yesterday. The cell near Minneola did display a persistent mesocyclone and displayed a hook echo on several scans. The cells further west also showed some weak convergence signatures with high SW also located in the area of the reported tornadoes. However, there were at least a couple reports that looked to be associated with very weak showers or possibly even just the boundary. There was one report into DDC for a possible mile-wide multi-vortex tornado. Now we know that intial guesses on size can sometimes be far off but still that would be a little extraordinary by cold core standards.

A good example of what Jeff mentions is Janurary 28th. That was the tornado that formed where two weak boundaries and where a weak tower was forming. The result was a tornado that caused some damage at a car dealership. As for yesterday, I got home just in time to grab the 21z RUC nexlab products, so I plan to have something put together later today.

Congrats to Simon Brewer & Mike Umscheid. When I saw that cell near Dodge City I thought there was a pretty good chance Mike would be on it, look forward to your pics guys!
 
10/26/06 Southwest KS. Tornado outbreak

Even though my chase with Dave Ewoldt was a successful one... no tornadoes were had... the cells in Cowley Ks. toward dusk tried hard to tornado... lots of light to moderate, broad rotation but with lots of turbulence... for a more indepth review of my chase.. refer to my chase summary that I posted.

Dave and I, as well as other's on this list pretty much knew where to go... capes were barely adequate, shear was more than exceptable, especially low level shear as the vortmax was beginning to eject east aiding in the lift... surface winds as advertised by short term models backed as the day progressed at our location along the warm front just north of the OK/KS border . But the negatives, a big dry punch in the mid levels may have impeded the processes... moisture, and perhaps too much flow at the 500mb. level(?)

But ... what about the DDC area... who saw this coming?? So here are some questions I impose on the group to figure this all out.

1.) Was all the vertical vorticity that I'm sure was a catylist to these tor events not recognized earlier and thus raise the eyes of forecasters?

2.) These tornadoes occured more on the northwest side of this shortwave/vortmax... how unusual is that? What case studies similar to this in the past have occurred?

3.) Did the low LCL's and boundary interactions also contribute to this unforecasted event? I noticed after the fact that covergence was quite evident south and west of DDC... Was this stronger than forecasted?

4.) Could this been caused by a mesolow that branched off from the main vortmax to the SE.?

I'm looking forward in reading what responses can come from this... I'm especially looking forward in reading what Jon Davies has to say regarding this event. I'm also hoping that Simon Brewer will chime in here as he pretty much had this pegged from early on and as noted in the summaries had a successful intercept ...great work !

Rocky&family
 
Congratulations to all that chased to CC setup yesterday. It is great to see more and more people recognizing and chase these setups. I have to say I am very jealous and annoyed with myself for passing on two (Sep 21st and Oct 26th) excellent CC setups in just over a month.

I would be interested in hearing some comments on why these cold core outbreaks are so difficult to forecast. The SPC didn't have a risk for tornadoes or severe thunderstorms in that region. Even in their updates throughout the day I didn't see a risk added.

What makes the cold core outbreaks so difficult to forecast?

In my opinion, the hardest thing about forecasting cold core setups is ignoring everything you think you know about instability. The low CAPE values typically associated with CC setups are not representative the true environmental instability. As long as you have relatively clear skies over the surface-low warmfront intersection and OK moisture (50+ dewpoints) you will have all the instability needed for strong updrafts and low-topped supercells. Finding your target couldn’t be easier. Just go to the warmfront! Storms usually initiate on the WF or on the dryline/dryslot and move north to the warmfront and produce tornadoes.

LT supercells often appear as clusters or lines on radar, but the updrafts are very small and they don’t need 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 true structure. This in my opinion 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" and 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. It is my firm belief that DOW data from these types of storm would show that they are virtually identical to your typical tornadic supercell with the one exception being size.

Here are the SPC storm reports and the 13z tornado probabilities from some recent cold core events. Can you say warm sector bias?

October 26, 2006
061026_rpts.gif

day1probotlk_20061026_1300_torn_prt.gif


September 21, 2006
060921_rpts.gif

day1probotlk_20060921_1300_torn_prt.gif


March 20, 2006
http://www.spc.nssl.noaa.gov/climo/reports/060320_rpts.gif
http://www.spc.nssl.noaa.gov/products/outlook/archive/2006/day1probotlk_20060320_1300_torn_prt.gif

November 27, 2005
http://www.spc.nssl.noaa.gov/exper/archive/events/051127/act-plot.gif
http://www.spc.nssl.noaa.gov/products/outlook/archive/2005/day1probotlk_20051127_1300_torn_prt.gif

April 10, 2005
http://www.spc.nssl.noaa.gov/climo/reports/050410_rpts.gif
http://www.spc.nssl.noaa.gov/products/outlook/archive/2005/day1probotlk_20050410_1300_torn_prt.gif

March 21, 2005
http://www.spc.nssl.noaa.gov/climo/reports/050321_rpts.gif
http://www.spc.nssl.noaa.gov/products/outlook/archive/2005/day1probotlk_20050321_1300_torn_prt.gif
 
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Just an observation from having watched this event on and off from work. From a pattern recognition standpoint, I think that the location of the Clark/Ford county tornadic storm couldn't have been more classic with respect to the location, character, and movement of the mid-level vort max. The unusual thing in this event IMO was the fact that the storm was generally well into the northwest quadrant of the surface low (which had shifted into northcentral OK IIRC), along a trailing quasistationary boundary (perhaps an old occluded front) within relatively lower theta-e air. That morning, when I looked at short-term forecasts, sfc winds wanted to go northerly in that area, and MLCAPE was fcst to be less than 100j/kg. I accordingly disregarded the SW KS target. Looking back at the mid-levels, I kind of kicked myself afterwards. Obviously, microscale conditions allowed for tornadic low-topped storms even though the surface pattern was a little different than what i'm used to seeing with these cold core events.
 
According to my research, 10-26-06 preliminary report of
26 tornadoes (if they all verified) will set the new October
daily record for tornadoes for Kansas (1950-2006 data)

Mike
 
Scott, thanks for the analysis and links to archived data. Does anyone happen to have the surface vorticity RUC data from around this time? I'm interested because we have a fairly unique case here, not only with low topped storms, but there is some degree of "extra" vertical stretching ongoing as the upper low exits the higher terrain of the Rockies.

I'm willing to bet there was a local maximum in the area of tornadogensis given the strong convergence into the E-W surface trough and strong N-S thermal gradient on top of that.

Regarding CAPE, one thing that Jon Davies and others have tried to demonstrate in these cases is that "some CAPE" is enough, as long as it provides an updraft deep enough to concentrate the high boundary layer shear. Often true of these cases, cloud tops are only on the order of 20Kft with very little lightning.

I noticed that in Mike Umscheid's report he kept referring to the low overcast and "grunge" near the storms. A direct assessment of the low LCLs and LFCs, also suggesting that the very moist parcels near the surface would lend to a higher virtual temperature and thus higher CAPE than would be predicted by the RUC.

The "westward" advection of moisture along surface boundary is likely largely due to persistent upslope flow that had been ongoing for days north of a qausi-stationary warm front...finally drawn around the surface occulusion as it passed by.

It's funny how this case becomes obvious in hindsight, so it may be interesting to go back 12-48 hours before the event and see if these hints (besides the obvious upper low and speed max) were available.

Evan
 
Does anyone happen to have the surface vorticity RUC data from around this time? I'm interested because we have a fairly unique case here, not only with low topped storms, but there is some degree of "extra" vertical stretching ongoing as the upper low exits the higher terrain of the Rockies.

I'm willing to bet there was a local maximum in the area of tornadogensis given the strong convergence into the E-W surface trough and strong N-S thermal gradient on top of that.
22Z SPC graphics of surface vorticity and 3 km CAPE on National Scale
http://www.spc.noaa.gov/exper/ma_archive/images_s4/20061026/22_3cvr.gif

22Z surface plot, MSAS SLP and "RUC40" initial analysis of surface relative vorticity
http://members.cox.net/gdp416/METAR_Plot_20061026_2200.png
RUC analysis of surface vorticity maxima looks to be displaced too far south given observations

22Z Digital Atmosphere surface plot and surface relative vorticity
http://members.cox.net/gdp416/KP28_22Z.gif
 
Input to your 10/26/06/ discussion

I and chase partner Rick Druse were on the Minneola storm on the 26. This storm that produced all the tornado reports was to me had classic super cell structure. The number of tornadoes that were reported fell short of what we observed.Threre was a very large well formed meso very low to the gound with multiple vortices rapidly forming and disapating. This is what I reported as the large multi vortex tonado. At the same time south of a very clear boundry,on just building towers were landspout tornadoes occuring .On this boundry at the surface you could move literally feet and be in cold air with NE winds 30 to 40 mph to south southwest warm winds of about 10 to 15 mph. You can go to the web site dodgecity.com and click on spotted scroll down to you spotted to 10/26/06 tornadoes and find pics of this event. I hope this is of help to you in your break down of this event
 
Jeff,

I was working the 4pm-12am shift at SPC. The first tornado warning was issued (literally) as I walked into the operations area, and that warning included a report. I took over the shift around 4:05 pm, and by 4:20 pm was initiating a conference call with DDC and ICT for what became tornado watch #839.

Fifteen minutes is not much time to get your bearings, especially when I had to at least consider some aspects of the "main" outlook areas in OK/TX. We did not amend the outlook because the expectation was that the event would likely wind down before 01z. In other words, we missed our opportunity to forecast the tornadoes, so we were left with a short term "reaction" in the form of the tornado watch. The worst case scenario is when an unexpected event corresponds to shift change, as was the case Thursday afternoon.

Rich T.
 
Jeff,

I was working the 4pm-12am shift at SPC. The first tornado warning was issued (literally) as I walked into the operations area, and that warning included a report. I took over the shift around 4:05 pm, and by 4:20 pm was initiating a conference call with DDC and ICT for what became tornado watch #839.

Fifteen minutes is not much time to get your bearings, especially when I had to at least consider some aspects of the "main" outlook areas in OK/TX. We did not amend the outlook because the expectation was that the event would likely wind down before 01z. In other words, we missed our opportunity to forecast the tornadoes, so we were left with a short term "reaction" in the form of the tornado watch. The worst case scenario is when an unexpected event corresponds to shift change, as was the case Thursday afternoon.

Rich T.
Thanks for the comments. I was curious what the thinking was on your end of the line. These cold core events seem to be extremely difficult. It seems like there have been more over the past couple of years than in the past. That may not be the case though.

I would be curious if SPC does a post analysis "meeting" on events like this and try to determine what went wrong or could have gone better.

Great job this year on the forecasting for the PAH Region. We have been hit hard for several years now. Lot of destructive tornadoes. Everyone over here pays close attention to what your office says and does.
 
There are a couple of relatively recent publications focused on cold-core setups:
Preliminary Climatology of Tornado Events with Closed Cold Core 500mb Lows.(Davies and Guyer)

Guyer, J.L., and J.M. Davies, 2006: Enviroment Characteristics Associated with Tornado Events near Closed Cold Core 500 MB Lows. Preprints, 23nd Conf. Severe Local Storms, St. Louis MO.

I think the biggest problem lies in the fact that the parameters of "cold-core" setups are far from what we've come to expect from tornadic supercell cases. In addition, there's even some debate as to whether these events are nonmesocyclone tornadoes or mesocyclone tornadoes associate with relatively short-lived mini- or low-topped supercells. I'll be presenting a poster at the upcoming SLS Conference that focuses on the 3-20-06 NW OK cold-core tornado, which had dewpoints below the common lower threshold set forth by a previous Guyer and Davies paper (~50F).

From a chasing perspective, I don't think they really are that difficult to forecast. The cold-core setups that seem to produce are those with a surface low <150km from the center of a 500mb low, a distinct pseudo-occludded front, and steep low-level lapse rates that yield some decent low-level CAPE. The boundary involved yesterday was well-developed and clearly evident on local 88Ds. Earlier this year, on 3-20-06, we parked ourselves along a similar, well-defined surface boundary in NW OK, and waited for a moderate convective cell to approach, interact with, and cross the boundary. Well, not entirely unexpectedly, the cell quickly developed substantial rotation, took on supercell characteristics (RFD clear slot, wall-cloud, etc), and produced a tornado; all the while it, was snowing 30-40 miles to the northwest.

The last line of my last post in the FCST thread:
" There may be a risky cold-core play across far nw OK and eastern OK panhandle if the 12z RUC verifies."
This makes my choice even more frustrating, since I looked at the cold-core play (in the mid-morning, it appeared as though the front may stay in OK, which is why I mentioned far nw OK... Obviously, the front ended up in sw KS, so adjustment would have been needed!). So, why did I chase south of ICT yesterday instead of south of DDC yesterday? The same reason why I chased the warm-sector several times during the spring of 2005 while the cold-core play was lighting up to my northwest... It's tough for me to drive hours to a location, hoping to see tornadoes, with temperatures in the 50s and dewpoints even lower, when I can play a more "typical" warm-sector setup (dewpoints in the 60, good veering wind profile resulting in substantial low-level shear, etc). This will change next year, as I've realized that the cold-core target has been remarkably consistent the past 2 years, particularly since many of the cold-core days in the past couple of years have feature warm-sector setups that have had to deal with marginal moisture.

It is very important to determine, however, if yesterday's tornadoes really were associated with low-topped supercells with (relatively) deep, persistent mesocyclones (a little redundant, since supercells, by definition, contain deep, persistent mesocyclones). I haven't looked at radar data from the event, but there's the possibility that these were nonmesocyclone tornadoes caused by intense stretching of ambient vertical vorticity not associated with deep, persistent mesocyclones. This is a very important distinction to make! Many landspout tornadoes on the Front Range are caused by strong low-level vertical acceleration associated with building TCu stretching vertical vorticity in or near a misocyclone. A "cold-core event" typically refers to situations in which convective cells "feed off" the ambient vertical vorticity along a boundary and develop relatively persistent, deep mesocyclones. On the 3-20-06 case, the cell near Putnam indeed did develop a deep, persistent mesocyclone, along with other supercell "features" (RFD clear slot, etc, as noted earlier). I suppose much of this comes down to the depth and duration of the rotation in the cell. Were they really tornadoes associated with supercells / mesocyclones, or were they more shallow, landspout-ish tornadoes? It's not entirely a clear-cut distinction in the first place, and I haven't looked at any radar data to determine either way.

The only mention by DDC that I read in yesterday afternoon's AFD was this: " VERY LIMITED CAPE SHOULD KEEP STORMS BELOW SEVERE LEVELS."

Did the SPC update their 20z outlook to account for higher tornado probs when they issued the tornado watch for SW KS?

Thanks, Jeff, for considerations. Cold core setup is so much productive also in Italy during autumn.
Anyway following the last synoptic situation of 26th october , it seemed to me that the place where tornadic supercells occurred was not the right one where tornadogenesis is most favourite (correct me if I'm wrong).
From Davies site there's a fine graphic where it is well explained.

composite_daviesguyer2004.gif



In our case 500mb low was collocated less than 320km away from the surface low and this was a good sign that could indicate that tornadic low topped supercell could occur. But if you see from the surface analysis map where is collocated the intersection between cold front and warm front (major probability for tornadic development) at 21-22Z of october 26th(the time of the tornadic development in Minneola)it appears that this intersection of those boundary is about in Enid Ok, that is about 200miles far away from Minneola. For this reason it resulted difficult for me to understand why tornadic development was so distant from the forecasted one.
Anyone can give me an answer?
 
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