Moderate Threat Risk for Eastern NE 6-26-2011

[Rob Wadsworth]

Mods: didn't want to post this in the wrong section. Please move if necessary.

I was just very curious why there isn't any discussion in the Advanced Forecast section on today's Moderate Risk for E NE?

Seems the CAPE values are 4000 J/kg presently across all of NE, according to the RUC. Dewpoints are roughly ~72 degrees too. Helicity is best on the WC part of NE and centrally along the NE SD border ATM. The cold front is of course moving from the NW to the SE, located centrally in SD. The lapse rates in E NE are improving ATT. 850mb winds from the SE are approaching 40kts.

Like to learn from what looks like should happen - or not.

BTW - Is anyone on this chase?

 

[Ben Corby]

Plenty of people on this one. I debated going this morning, and opted against it. I'd be potentially as far east as Lincoln or Omaha by the end of the day (~8:30/9:00 PM), and would then have an eight-hour drive ahead of me before starting work at 7:30 AM tomorrow.

Looks like a great setup for severe weather, though, and good luck to those who are on it!

 

[Andy Jackson]

Yeah it is interesting how the probabilities are. The extreme instability forecast coupled with the upper level energy moving into eastern Nebraska should produce some powerful stuff. I'm sure most will be chasing this event.

 

[Brett Nickeson]

This setup was looking great last night and into early this morning. However, I'm a little concerned at the lack of surface heating in eastern Nebraska due to the complete cloud cover in the area. It's going to be hard to break the cap if these clouds stick around. The 16Z RUC still has the cap completely broken in east-central and SE NE by 21Z, so I guess we'll see what happens. I'm still torn on what target to shoot for. I could go south just north of the warm front into a more unstable environment but with less backing winds, or I could go further northeast outside of Columbus which has better backing winds but less surface heating. I might wait on this one a bit more here to see how it evolves. On paper the setup looks incredible but for some reason I'm pessimistic on getting powerful sup's. It just doesn't feel right outside.

 

[Rob Wadsworth]

What are the parameters that would change these from tall, low based (high CAPE value and high dew points) hailers into dangerous tornadic supercells? Since this is a learning thread, I don't mind asking the question. 300mb winds are due East - BTW.

I didn't look at any hodograph as yet; don't have much confidence how to read them well enough either. But with lapse rates getting better (haven't rechecked that yet); that would mean the vertical shear would have to be more profound. Just not quite sure how to read and understand what is happening at 500mb. I think this is one of the more important parameters that account for putting a spin on a cell. With 300mb winds E, The cold front moving to the SE, and surface winds from the SE at 40kts; what direction would the 500mb shear need to be? Anyone care to address this? All ears here . . .

 

[Andy Jackson]

I didn't look at any hodograph as yet; don't have much confidence how to read them well enough either. But with lapse rates getting better (haven't rechecked that yet); that would mean the vertical shear would have to be more profound. Just not quite sure how to read and understand what is happening at 500mb. I think this is one of the more important parameters that account for putting a spin on a cell. With 300mb winds E, The cold front moving to the SE, and surface winds from the SE at 40kts; what direction would the 500mb shear need to be? Anyone care to address this? All ears here . . .

Look at the SPC mesoanalysis page. The question mark icon besides each parameter will help steer you to understand what each parameters significance is. Remember people go to 4 years of college to learn about this stuff so it's not going to be an overnight learning experience, or maybe it is.

 

[Brett Nickeson]

Well today's threat dissipated in a hurry. I'm sitting in York, NE where it's 69 degrees and misting with a light northeast wind and a nice strengthening cap. I see the SPC just removed the Moderate threat for the area as well. I don't think the models could have handled today any worse. I'm not sure anything will come out of this in SE NE today.

 

[Jeff Duda]

This was a pretty classic SPC 15% hatched tornado bust. They are notorious for overdoing the threat for a situation like this. Yes, instability is extreme and shear is sufficient for supercells and tornadoes, but take one look at the 700 mb plots and visible satellite. The entire 15% area was socked in under low stratus, which maximizes the loss in destabilization, until just the recent hour or so. Take that with 14-17 C H7 temps moving in and you have the perfect recipe for a cap bust, which SE NE is going to be. One more thing, the models have not been accurately predicting the northward progression of weakly forced warm fronts across the central plains lately. This is just another example. Thus your only real surface forcing is sitting under a nuke-proof cap. I decided to venture out when I saw the stratus deck eroding rapidly at around 1 PM, but it quickly filled in again and the W-E oriented band of showers developed in NE, thus officially halting any destabilization from there and north (and likely somewhat south due to cold pool propagation). I turned around about 1.5 hours after leaving and ended up seeing more impressive stuff 2 hours from home (non-severe hail near Creston) than I would if I had gone to SE NE.

Rob, to answer your question about why there is no discussion in the target area forum: it's probably a combination of the rule changes restricting and confusing some people, a bit of an exodus over to CF (but it's been pretty quiet even over there), and what may be the biggest reason (at least for me) - as active as a season as this was especially in April, I think people are just exhausted of the season.

 

[jshields]

i'm currently sitting in beatrice nebraska about 45 minutes south of lincoln. the skies have cleared here and it is soupy. last hours obs showed 82/77!! according to the spc the cap is gone in extreme southern nebraska and northern kansas. not so sure about that since spc also showed 14-16 C 700 mb temps. i know the ruc overdoes cape but its now showing cape values over 6000, supercell composite is 50, and the sig tornado index is maxed out over a large area at 12 due to effective srh of 400!! if something can pop it should go severe VERY quickly. there is an ofb that has blown off the mcs to the north so hopefully that will be enough. right now watching small towers go up and then fall apart. if something doesn't go soon i might head back north towards omaha to catch the squall line that is heading southeast towards east central nebraska. i want a tornado though!!

 

[Jeff Duda]

according to the spc the cap is gone in extreme southern nebraska and northern kansas. not so sure about that since spc also showed 14-16 C 700 mb temps. i know the ruc overdoes cape but its now showing cape values over 6000, supercell composite is 50, and the sig tornado index is maxed out over a large area at 12 due to effective srh of 400!!

Know that the mesoanalysis data on the SPC site is coming from forecast hour 01 RUC model data. That means that what it says for observed data is actually a one-hour model forecast adjusted to come closer to matching the current observations. Thus you tend to get some effect of the model forecast in the analysis. I'm pretty sure that surface-based parcels in southern Nebraska are not uncapped. They may not have a ton of CIN left, but it's probably higher than what is being indicated. Also, it sounds like you already get this, but the reason the composite parameters are so high is because the CAPE is extreme. The CAPE part of the supercell composite parameter and significant tornado parameter is likely driving the output value significantly higher. Unfortunately, just because such extreme CAPE exists doesn't mean it will ever be realized. Such is the case frequently in IA and NE, and KS this year. If only a storm would go up there...

 

[Rob Wadsworth]

Thanks for that explanation, Jeff.

So; what would b a more acceptable H7 temp? They were too warm and supported the inversion layer - eh?

And why does the SPC get every bodies knickers in a bunch when they knew the cloud cover wasted the destabilization? That makes them a whole lot less credible over the last two weeks. 3 and 0. Maybe they should put the same team they had last year on the SPC; they were pretty right on. Time to change the pitcher . . .

I rolled out to NE Nebraska on Hwy 20 four hours ago. Just got back in. A bridge on Hwy 20 - about 90 mi E of Oneil NE had been washed out. Didn't want to have to beat a hasty retreat with a detour 12 miles long. No way. The Missouri river was immensely swollen; I saw trees 15-20 ft under the water that used to be 5 ft above the banks. It doesn't look too good for the farmers out along the river. Sioux City has got to be feeling pretty uptight right about now too.

 

[Dan Robinson]

Jeff is right, the parameter bullseyes are typically not good for targeting. You have to get a storm in the environment to take advantage of the parameters, which many times doesn't happen. Many times with the big CAPE/shear/STP/SC bullseyes (south of a warm front, for example), the place to target is the front, even though the parameters are significantly reduced there in comparison. The parameter composites are a lot like SPC outlooks in that they don't help much with pinpoint chase positioning, you still have to do all of your traditional analysis.

 

[Skip Talbot]

So; what would b a more acceptable H7 temp? They were too warm and supported the inversion layer - eh?

http://www.jondavies.net/700mbTcap/700mbTcap.htm

And why does the SPC get every bodies knickers in a bunch when they knew the cloud cover wasted the destabilization? That makes them a whole lot less credible over the last two weeks. 3 and 0. Maybe they should put the same team they had last year on the SPC; they were pretty right on. Time to change the pitcher . . .

Its easy to criticize from the bleachers, but really the SPC forecasters are some of the best in the world. When you forecast you are working without all the variables and some that are misleading. Was a moderate risk for tornadoes warranted? Several of the numerical models indicated storms going up in an extremely favorable environment for tornadoes. However, if you switch up a few of the ingredients, you wind up with nothing. It was a good guess given the data we had to work with.

The cloud cover didn't waste the destabilization in that it prevented it from being used/realized. If anything the cloud cover hindered the northward progression of that warm front and destabilization north of the warm front. What really wasted the unstable airmass (in terms of initiating it) was a source of good lift, and capping issues. We had broad zonal flow and a fairly mediocre surface pattern over the moderate risk region, neither is going to support strong forcing. What I noticed that was severely lacking today were the low level lapse rates. Even right on the warm front where the airmass was strongly to extremely unstable, low level lapse rates were hanging around 5, which is awful. You need those lapse rates a lot higher to get really strong updrafts and convection to come up off the surface. Eroding that cloud cover a lot earlier would have helped that situation, and for awhile it looked like it might happen. When that cloud cover burned off by early afternoon with a nice robust cumulus field coming out of Kansas, I was kicking myself for not being out there. The capping turned out to be a bigger issue than I originally thought (last night's models showed big holes in the cap). It looked like a shortwave or two went through the area in the afternoon as you could see waves in the cu fields, but then it went quiet just as the cap was supposed to open up the most before filling in again. Had those clouds burned off earlier, and maybe those shortwaves been a little better timed, we could have seen a few supercells go up in the moderate risk area and maybe have dropped some large tornadoes. It doesn't take much to botch an entire forecast.

Jeff is right, the parameter bullseyes are typically not good for targeting.

That's right, in fact forget the bullseyes completely. You should be looking at where your sources of lift are (boundaries and upper level dyanmics) and where the cap is weakest. Then you can take a peek at what the severe parameters are like in those areas. All the cape and helicity in the world is not going to do you any good if there is no source of lift and you have a bit of a cap hanging around. Your sources of lift are often on the fringes of those better parameters. Play the gradients, not the bullseyes.

 

[Rob Wadsworth]

Thanks for filling in a few more blanks, Skip. My track record with cap busts is appalling. Chalked up yet another today out in NE Nebraska. Yep; I took the bait. Truth is, I got here in IA on June 3rd and this year is turning out to be the first year w/o bagging a tube. Just got antsey and went out anyway.

Guess I'll need to study more details this year if I'm going to get one next year, Lord willing . . .

 

[jshields]

oh yeah i know all about days of summer with extreme values on several severe weather indices, but if you have nothing to set anything off they do go wasted. i often take a look at soundings during a warm humid summer afternoon just to see the extreme amounts of CAPE going "wasted". today was pretty oppressive temp and humidity wise. the clouds were literally almost scraping the ground once you got near the storms.

i stayed right on the warm front, never ventured further south into northern kansas where the CAPES were 7000. i watched the 700 temps just keep going up and up and knew there had to be a cap that was going to hold, despite what the spc was showing. i seem to remember the convective outlooks talking about a good piece of energy ahead of the coldfront coming across that was supposed to set off the storms, but apparently it wasn't timed right? skip- i remembered looking at the low level lapse rates and seeing that huge area of really low numbers. i have to admit that is something i don't always look at or when i do, i don't pay much attention to it. something with forecasting, etc. i need to work on!!
i only stayed in beatrice about 30-45 mins watching a few towers die before i headed north to intercept the line moving east/southeast across the state. intercepted the end of the line northwest of lincoln right before it went tornado warned. didn't see anything great rotation wise but visibility was pretty bad due to all the low clouds. experienced winds of 60 mph and up to quarter sized hail. also there was buckets and buckets of rain that came down. with all that moisture i'm not surprised! was treated to a nice lightning show and mamatus clouds on the way home into omaha on the backside of the storms. another day without a tornado, but at least it wasn't my fault today!!