04/13/06 DISC: Northern Plains

[Jeff Miller]

Starting a thread for discussion on severe weather on 4/13/06 in the Midwest states of Iowa and Illinois.

Third party media reports and confirmed SPC reports indicate damage from tornadoes from numerous supercells in these areas. Per ST Mod, carrying over discussions here.

 

[Jeff Snyder]

Just a mod note, the DISC thread type was intended more for post-event discussion or media reports, not necessarily real-time media, NWS, or spotter/chaser reports. As the rule stands now, however, it does read that all third-party reports belong in a DISC thread, which is why I requested that media reports should be carried on over in this thread. So, please paste third-party reports here.

 

[Jeff Miller]

SPC STORM REPORT:

MAJOR STRUCTURAL DAMAGE TO LARGE SHOPING BUILDINGS AT INTSCTN OF Q18 AND STATE HIGHWAY 1. LOTS OF DEBRIS AND DOWNED TREES. (DVN)

Wow. My hope is everyone is ok here. Hopefully the shopping buildings were closing and not many were there at the time.

 

[J.B. Dixon]

New pictures being posted right now on the Cedar Rapids Gazzette web page from downtown Iowa City, including a great shot of a lightning-backlit funnel/tornado.

www.gazetteonline.com

 

[Jayson Prentice]

Media reports that traffic in Iowa City is terrible, people are trying to travel with debris and other damage in the area. People have been evacuated by some areas due to natural gas leaks as well. I did recieve word from a student at Iowa that may help show how strong this tornado was, reported that near the Menards that had the roof collapsed completely was a Dairy Queen that is supposedly completely destroyed.

Very lucky that there havne't been more injuries or even deaths in the Iowa City area given that some reports have indicated that they did not know where the tornado was. Not sure why or how, but that is the info that I have right now.

 

[Sam Sagnella]

KCRG has posted a photo gallery of viewer-submitted photos of the event. Most of these are hail (some quite large) but there are a couple in there of wall clouds and such.

http://community.webshots.com/slideshow?ID...3439&key=ijLEFw

EDIT: KCRG-TV: "Video from Mark Geary from south of Van Horne in Benton County" This is from the location where a man was briefly trapped in his home earlier tonight. They keep adding new videos all the time to this page http://www.kcrg.com/news/local/2632711.html

 

[James Musal]

Media reports that traffic in Iowa City is terrible, people are trying to travel with debris and other damage in the area. People have been evacuated by some areas due to natural gas leaks as well. I did recieve word from a student at Iowa that may help show how strong this tornado was, reported that near the Menards that had the roof collapsed completely was a Dairy Queen that is supposedly completely destroyed.

Very lucky that there havne't been more injuries or even deaths in the Iowa City area given that some reports have indicated that they did not know where the tornado was. Not sure why or how, but that is the info that I have right now.
[/b]

For reference that DQ is JUST south of University of Iowa campus and in a light commercial strip (several fast food and light retail outlets). It is indeed very lucky that there aren't more injuries and people in that area presumably heeded the warnings.

Raw storm photos can be found here: http://mesonet.agron.iastate.edu/cases/060413/

The best link for local info:
KCRG TV 9 Cedar Rapids/Iowa City this has video reports

KWQC TV 6 Quad-Cities this one does not have much but covers the Muscatine area

//edit: I was a bit too slow to post these links. My appologies

 

[J West]

I moved this over here to better comply with the rules:

Numerous reports from Dane County regarding big hail...Quick check shows a few verified reports of 3.0" hail, with some reports from the UW-Madison campus. I called work, and a Trooper reported getting softball size hail on the west end of Jefferson county when the cell went through, and a Waukesha County Sheriff squad lost a window to baseball+ size hail in the Oconomowoc area.

 

[Sam Sagnella]

First official report of a fatality from the storm that passed through Muscatine County.

0920 PM     TORNADO          NICHOLS                 41.48N 91.31W 
04/13/2006                   MUSCATINE          IA   LAW ENFORCEMENT 

            *** 1 FATAL *** MOBILE HOME DESTROYED. STORM TRACK 
            ESTIMATED AT LEAST 4 TO 5 MILES IN LENGTH. STORM SURVEY 
            WILL BE DONE IN MORNING. TIME ESTIMATED.

http://kamala.cod.edu/offs/KDVN/0604140455.nwus53.html

Frankly, I'm surprised/thankful this was the only one considering the population density of the areas affected by tonight's apparently significant tornadoes.

 

[Jeff Miller]

NEW TOR WATCH issued now.

I normally am not very inquisitive concerning how forecasts are handled by the Storm Prediction Center, but last evening to this morning have raised some questions. The following is NOT a derogatory statement toward the Storm Prediction Center. It is an honest request for answers on things I apparently do not yet understand.

Last night, we had apparantly significant tornado activity which caused one fatality, and injured at least two individuals. Significant damage was reported in Iowa City, and tornado damage reports were common throughout much of SE Iowa from evening continuing to morning. Several large supercell thunderstorms had mesos, and reports of large tornadoes were coming in that were spotter-confirmed.

All during this event, the watches remained as severe thunderstorm watches despite more than 2 supercell thunderstorms with mid and low level rotation, strong couplets and confirmed wall clouds, funnels and tors that threatened populated areas.

Finally this morning at around 1:50, a new Tornado Watch was issued for the same storms farther east, but long after the worst of the tornaodoes apparently occured.

I have every confidence that SPC did all they could and followed every guideline, and I applaud them for working as hard as they did. They do a superb job at what they do and not many can fill their shoes.

My question is: What lacked the SVR boxes to be upgraded to TOR boxes? what is it about the event that lacked the parameters and conditions for tornado watches? were tornado watches warranted? Was this a scenario where an MCS was simply not expected to go tornadic, or the tornadic storms were expected to die off but didnt? Was something askew about the whole event that caught even the most experienced forecasters by surprise?

Again, thank you SPC for all you do, this is not derogatory. I simply ask for answers because honestly, I am quite perplexed, and I dont know or not if I am the only one who has wondered this this morning.

 

[Justin Turcotte]

NEW TOR WATCH issued now.

I normally am not very inquisitive concerning how forecasts are handled by the Storm Prediction Center, but last evening to this morning have raised some questions. The following is NOT a derogatory statement toward the Storm Prediction Center. It is an honest request for answers on things I apparently do not yet understand.

Last night, we had apparantly significant tornado activity which caused one fatality, and injured at least two individuals. Significant damage was reported in Iowa City, and tornado damage reports were common throughout much of SE Iowa from evening continuing to morning. Several large supercell thunderstorms had mesos, and reports of large tornadoes were coming in that were spotter-confirmed.

All during this event, the watches remained as severe thunderstorm watches despite more than 2 supercell thunderstorms with mid and low level rotation, strong couplets and confirmed wall clouds, funnels and tors that threatened populated areas.

Finally this morning at around 1:50, a new Tornado Watch was issued for the same storms farther east, but long after the worst of the tornaodoes apparently occured.

I have every confidence that SPC did all they could and followed every guideline, and I applaud them for working as hard as they did. They do a superb job at what they do and not many can fill their shoes.

My question is: What lacked the SVR boxes to be upgraded to TOR boxes? what is it about the event that lacked the parameters and conditions for tornado watches? were tornado watches warranted? Was this a scenario where an MCS was simply not expected to go tornadic, or the tornadic storms were expected to die off but didnt? Was something askew about the whole event that caught even the most experienced forecasters by surprise?

Again, thank you SPC for all you do, this is not derogatory. I simply ask for answers because honestly, I am quite perplexed, and I dont know or not if I am the only one who has wondered this this morning.
[/b]

This was an interseting day that will likely garner the attention of a few case studies. I'm sure someone will talk about it at the next Iowa conference. Most of us including myself were focused on the warm frontal boundary located in southern MN and southwest WI. This was where the various models were advertising convection with the backed surface winds and reasonable dewpoints. Look no further than the various AFDs and ST forecast posts. What was less obvious was a subtle trailing trough which was in fact in some of the previous day model runs. The warm sector looked like it was going to be fairly capped though not unbreakable. One of the GEM runs and perhaps a GFS run did spark some convection along that boundary but consensus was for the action to be right along the warm front. What was not advertised is surface winds backing to the southeast along the trough. There was plenty of advertised shear in the warm sector but southwesterly surface winds are generally not the ideal direction to get those long loopy hodographs and 0-1km SRH. I went to the office and was tasked with drawing grids for IADoT forecast. A quick glance at the surface plot at 21z had the winds along the trough out of the southwest. Wnds along the warm front were behaving as usual. The moisture was pooling along the trough axis and never quite made it the the warm front where the action was expected to focus. This picture lead me to believe the tor threat in IA was quite limited. A cell quickly popped up along the trough and was just as quickly severe warned. The next hour the winds along the trough quickly backed to the southeast. This should have raised a red flag to all the forecasters but once you are stuck in a paradigm it is hard to shift. I cannot and won't speak for SPC but I do know the the various NWS agencies generally like consistency. If a product is issued than there needs to be significant overriding factors to change it. A blue box with an isolated tor threat doesn't necessarily justify an upgrade to a red box though I agree there were some warning signs that the situation could become quite volatile.

 

[Jeff Snyder]

I think the primary question mark for tornado activity was marginal moisture. Looking at surface obs and mesoanalysis, dewpoint depressions were quite high, yielding LCLs well above 1500m (up to 2200m in some areas near the supercells IIRC). Previous research has shown that the risk for tornadoes drops off markedly as the LCL approaches and exceeds 1400-1600m. A look at the 0z DVN sounding shows that the low-levels were quite dry (low mean RH), with LCLs in the 2100-2200m range. That's very high for any significant tornado activity. In addition, with the relatively dry low-levels, I think there was concern that cold downdrafts would be favored with cold pool / outflow collisions. Low-level and deep-layer shear was pretty strong given the WNW flow aloft, so supercells looked to be possible despite the relatively dry low-levels (the 0z DVN hodograph indicates that strong low-level shear was present, particularly given the ESE storm motion).

 

[Mike Johnston]

I agree this event will likely warrant some case study/retrospection.

My own thumbnail hypothesis is that instability built to optimal levels under the capping inversion, with the subequent energy release along a fairly sharp gradient along the southern boundary of the convective system. The last SPC outlook of the day anticipated MLCAPE values from 2,000 to 3,000 j/kg across E IA, and as it turned out the actual values appeared to be at the upper end of this range.

Despite the relatively high t/td spreads and LCL's, it appears the abrupt release of energy along the southern edge of the convection was sufficient to keep the cells inflow dominant for several hours. In addition, veering of winds w/ height was ideal (~90 degrees between 850mb and 500mb flow), maintaining rotating supercellular characteristics and delaying the anticipated evolution into a linear MCS.

As mentioned by other posters, the lack of moisture at the surface was a potential limiting factor, and was cited in a mesoscale discussion issued after the first severe watch, and even after the prolific mesoscale circulations and tornadic activity were observed. Again, purpose is not to play Monday morning quarterback w/ the SPC performance, but through exchange of ideas to gain an understanding of "why what happened happened."

There is a good paper by Craven and Brooks that sheds some light on the interplay of these factors, which I found very useful in attempting to understand this event:

http://www.srh.noaa.gov/jan/research/climo/climopaper.html

To give credit where credit is due....Nick Grillo's first forecast post on this setup (written two days in advance) was very prescient, so hats off to Nick!

 

[Rich Thompson]

NEW TOR WATCH issued now.


My question is: What lacked the SVR boxes to be upgraded to TOR boxes? what is it about the event that lacked the parameters and conditions for tornado watches? were tornado watches warranted? Was this a scenario where an MCS was simply not expected to go tornadic, or the tornadic storms were expected to die off but didnt? Was something askew about the whole event that caught even the most experienced forecasters by surprise?

[/b]

The original decision to issue a SVR watch was based on a deep mixed environment with potentially strong instability and sufficient vertical shear for supercells. Keep in mind that convective initiation was not clear cut yesterday, and I'm at least somewhat satisified that we issued before it got going in IA. All of the early focus was on the warm front well to the N, as mentioned by Jeff S.

I would have been better served in yesterday's case by *not* thinking much about the scenario. All of the short term models and problems with the moisture profiles. Even the RUC had some modest over-estimates of the moisture in SE IA with mean dewpoints of ~64 F, which was about 4 F too high. That moisture fed back into the various parameters, resulting in some of them being a bit too large. If you took the STP at face value and with no modification, you could justify a small TOR watch knowing that storms would be discrete supercells (which we did anticipate correctly). However, I may have looked at the situation too hard and convinced myself that storms would be relatively high-based with very large hail, and that destructive storm interference and cold pool formation would disrupt any tornado potential later in the evening across ern IA.

By the time we were convinced that the SVR watch was truly a mistake and that there would be more than 1-2 brief tornadoes, there wasn't much time to do anything to fix the problem. The majority of the tornado reports were clustered from ~0040-0220z. It was maybe 0130z by the time I truly believed the original watch was the wrong decision, which means we could have issued a TOR watch that would have covered the last 30-45 minutes of the threat (no longer than a single warning). The local office had things covered with TOR warnings, and I had missed my opportunity.

The second SVR watch (IL/WI) seemed to be a reasonable call with only 1 tornado report (we're supposed to issue TOR when we expect 2+ tornadoes). The late night TOR watch was issued by the next shift at both the SPC and the local offices, so I can't really speak for that one.

In summary, the timing and location of the initial watch was good, but the watch type was wrong. It's clear that my decision making and/or level of understanding need to improve to avoid any similar situations in the future.

Rich T.

 

[Gabe Garfield]

In summary, the timing and location of the initial watch was good, but the watch type was wrong. It's clear that my decision making and/or level of understanding need to improve to avoid any similar situations in the future.

Rich T.
[/b]

I woke up this morning and was shocked to see that damaging tornadoes took place last night. The synoptic/mesoscale environment didn't seem particularly favorable for the development of tornadoes, as previous posters have alluded to.

It's easy to get bent out of shape when a significant event happens that "flys under the radar." However, I think that it's simply impossible (at this time) to anticipate these events, because unique events occur every year. Furthermore, our collective level of understanding is still not where it needs to be to understand why tornadoes form in the first place. Thus, I think it is wise to give the SPC (and other such agencies) the benefit of the doubt in situations such as these. They are doing the best job they have with the knowledge that is available, and they should be commended.

Gabe