2012-04-14 FCST: TX, OK, KS, NE, IA

[Greg McLaughlin]

As for Saturday, the NAM is showing kinematics far too strong to create a favorable balance with (what it considers an inferior thermodynamic profile) I would think 3000-4000J/kg CAPE would be enough, that is a little more than the NAM is showing. Steeper mid-level lapse rates would help. We will need all the instability we can get to keep this from being a big shear fest. Another thing the NAM does is delay the deepening of the surface low in Colorado until early evening, then lifts the surface low quickly to the north from northeast Colorado to the Dakotas before shearing it out. We need the surface low to deepen earlier and hang down further south. Because the upper jet is so strong, I think we need much better backing of winds in the low levels to balance the kinemetic environment. If the surface low were to stay further south than what the NAM is forecasting while deepening it earlier in the afternoon, plus we get steeper lapse rates then Saturday has the potential to be a monster outbreak. That's what I have surmised after looking at the NAM. What do you all think of this?

And really all this appears to be coming down to is timing issues, but its anyone's guess as to how the timing and strength of these waves will pan out.....

 

[Tom Tackett]

Russ:

The only other time that a Day 2 Convective Outlook from the SPC has had a categorical High Risk issued was for the forecast day of April 7, 2006 (Outlook issued on 4-6). Unfortunately, it verified with "deadly" results.


http://www.spc.noaa.gov/products/outlook/archive/2006/day2otlk_20060406_1730.html

With regards to the set-up, watching for North Texas severe potential. Storms not expected to hit North Central Texas until the overnight with decreasing instability and strong linear forcing likely generating a linear system that will sweep through.

 

[cdcollura]

Good day all,

Right now I am targeting an initial stay in Wichita, KS (arriving on Kansas City about 5:30 PM this evening), do a quick setup, and drive there to Wichita for the night. As per SPC they have a 60% hatched and very enhanced wording on this forecast (issued Friday 4-13) with one statement stating "A High-End Life Threatening Event" in their text.

Basically, there will be two areas favorable for tornadoes and extreme weather, one the area pretty much along the I-35 corridor in N-Central Oklahoma extending into south Central Kansas (dryline, and the main focus), and another area spreading to the NE towards SW Iowa and into southern Nebraska (warm front). A 995 to 992 MB lee low is forecast to develop by 18z on 4/14 over W KS / E Colorado and that should cause the backing flow ahead of the dryline. This correlates to the H250 exit region of a 125+ knot jet stream. Winds remain SW and strong from H25 (250 MB) all the way down to 925 MB with a 70knot LLJ at 850 MB from the SSW and 50 knots at 925 from the S (with SSE at surface). Storm motions will be quite fast, so stay AHEAD of the early stuff.

The CAPE (3000+) has a large bullseye in the central N OK and S KS corridor, yet another one (2500 or so) near SE NE. Helicity (up to 400) is also maximised slightly east of the first "target" and a bit north of the SE NE one. Many models are showing precipitation breaking out in the 18-0z time-frame with a very sharp dryline west of the primary (OK-KS) target.

This has the potential to be a very devastating setup ... Stay safe out there - Chasers and non-chasers alike...

 

[Christopher E. Kincaid]

What about storm motions? I get the feeling they will be very fast - 40-50mph+. What do you guys think?

 

[Steve Sherrod]

I'm a newbie to trying to forecast so please correct anything I am saying wrong. Comparing the stp,cape and LSI index it looks like the ok/ks border north thru Wichita and up
to Salina is a target from around 6pm until around 1am. Am I reading this right? Early in the day Saturday the CAP is almost non existant until around 2pm then it goes to a +1
I live in Wichita and I am thinking start there or move to the east to handle the fast storm speeds. Did I read the parameters correct? Thanks everyone for all you input.

 

[mkavulich]

My first post here, so forgive me if I show a little ignorance.

It looks like the 12z NAM might be finally coming around and initializing some daytime convection, especially in south/southeast Nebraska near the triple point. I think the previous runs showing a complete daytime bust are pure nonsense, for 3 reasons: 1) both models show almost no cap throughout the afternoon, 2) there should be residual boundaries lying everywhere from the morning convection, and 3) the nose of a massive curved jet streak should intersect at least part of the warm sector starting mid-afternoon. I see the area south of the triple point in southeast Nebraska as a sure thing for daytime tornadoes (at least, as sure a sure thing as you can get with tornadoes). Am I off my rocker to think this?

 

[James Aydelott]

I worry that the northern target will not recover quick enough from morning convection. This could hinder real tornado potential but with at system like this it may not mater much.

Don't underestimate the effect a morning overcast/rain event can have. It will cause an e/w baroclinic boundary that will often act as another trigger, especially where it intersects a dryline/cold front.

Many major events have struck where we had morning precip.

 

[Jason Haller]

Don't underestimate the effect a morning overcast/rain event can have. It will cause an e/w baroclinic boundary that will often act as another trigger, especially where it intersects a dryline/cold front.

Many major events have struck where we had morning precip.

I guess I worry about it clearing quick enough. If it does then yes it could be just as explosive and have a warm front to work with. Guess I am just being nit picky with this setup.

 

[Derek Weston]

As for Saturday, the NAM is showing kinematics far too strong to create a favorable balance with (what it considers an inferior thermodynamic profile) I would think 3000-4000J/kg CAPE would be enough, that is a little more than the NAM is showing. Steeper mid-level lapse rates would help. We will need all the instability we can get to keep this from being a big shear fest. Another thing the NAM does is delay the deepening of the surface low in Colorado until early evening, then lifts the surface low quickly to the north from northeast Colorado to the Dakotas before shearing it out. We need the surface low to deepen earlier and hang down further south. Because the upper jet is so strong, I think we need much better backing of winds in the low levels to balance the kinemetic environment. If the surface low were to stay further south than what the NAM is forecasting while deepening it earlier in the afternoon, plus we get steeper lapse rates then Saturday has the potential to be a monster outbreak. That's what I have surmised after looking at the NAM. What do you all think of this?

And really all this appears to be coming down to is timing issues, but its anyone's guess as to how the timing and strength of these waves will pan out.....

The low had been settled by 21z on previous runs. I see now on the latest NAM that it drops from 996 to 992 at 0z. Not sure this necessarily changes anything, though.

2000-3000 j/kg with big time shear is a combination we've seen on many big spring outbreaks so that itself doesn't worry me too much. I think the numbers add up this way. But like you said... the worry is the balance of all the elements. As mentioned in my earlier posting about the only improvement I'd like to see is a bit more turning in the lowest levels -- more easterly component with the surface winds. But as is we're seeing some large looping hodographs by 21z... but for immense coverage -- storm competition throwing a wrench into things -- any storm realizing 2000 - 3000 j/kg in that sort of environment is going to be a threat to put down.

I do worry a bit about storm coverage being a tornado limiter with the sort of forcing we have... then again, we've all seen plenty of days with huge forcing and a plethora of discrete supercells. However... the nuances of predicting this sort of storm mode behavior are beyond my grasp.

All I can say is that the hodographs I'm seeing -- if instability is realized -- sure as heck look like tornadoes waiting to happen.

 

[Andrew Stoller]

If the 500 mb flow was more meridonal, I'd be more concerned about the strong upper forcing overcoming the lack of cap and somewhat more extreme instability. But 3,000 J of CAPE with deep layer shear vectors almost perpendicular to the dryline is text book, even of low level winds aren't as backed as you'd want in a perfect world. One thing I think might happen tomorrow, like what happened on Thursday, is the dryline retreating more westerly during the morning and overnight Friday, meaning initiation will be further west than anticipated.

There's a second dryline bulge and what looks like a smaller scale surface low forming to the south of the main surface low, right around the the Medicine Lodge area, per the NAM. Winds back a bit more right to the east/southeast of there and the dryline bulges a bit. That is also where moisture seems to converge more, maximizing CAPE, helicity, and EHI.

 

[jshields]

the 12Z NAM seemed to ramp up the low level helicity in several places as shown by the increased 0-1 EHI values all over the place vs previous runs. 2 areas i noticed were eastern nebraska, just east of the surface low where the winds are more backed to the southeast, and the second area as mentioned above by Andrew and Mike. I was going to head down towards Salina tomorrow, but now am torn between there and eastern Nebraska. Maybe I will start further north where initiation should be earlier, and then hop down the line after letting the previous storm blow past me. It'll be interesting to see how tomorrow mornings convection affects the placement of the warm front, instability, and also any OFB's up here in Nebraska

 

[Derek Weston]

the 12Z NAM seemed to ramp up the low level helicity in several places as shown by the increased 0-1 EHI values all over the place vs previous runs. 2 areas i noticed were eastern nebraska, just east of the surface low where the winds are more backed to the southeast, and the second area as mentioned above by Andrew and Mike. I was going to head down towards Salina tomorrow, but now am torn between there and eastern Nebraska. Maybe I will start further north where initiation should be earlier, and then hop down the line after letting the previous storm blow past me. It'll be interesting to see how tomorrow mornings convection affects the placement of the warm front, instability, and also any OFB's up here in Nebraska

Latest NAM makes Nebraska look awfully tempting. I noticed that about the backed winds... love the SE surface winds. Add to that... probably better storm motions on a better grid to chase on. My only concern is instability. I'll have to research that later today, but I'd say I'm a Nebraska lean as of now. What I wouldn't want to do is to get caught in no-mans land -- between two big clusters of supercells. While we may not have that behavior Saturday I've certainly seen it enough. (and as mentioned above... a few specific areas seem to be popping out) If I were in KS I'd want to be southern KS.

 

[Jared Orr]

I've been in love with the Northern Target for a couple days now...I just like the possibility of more isolated cells there. The considerations I will be monitoring most closely: Initiation time, interference between cells, and early afternoon clearing.

 

[Trey Thee]

Latest Day 2 SPC discussion tends to downplay the southern areas now...at least wrt violent tornadoes, but still keeping high risk....also added high risk in ern ne...

I'm not really sure why they weakened the wording so much for the southern area. Seems like a significant change from this morning. I've looking over the model data now and see nothing to indicate the likelihood of severe weather any less then it was this morning. Coverage is still in question so perhaps that's why?

To me it looks like we're going to have a major severe weather outbreak from the Wichita Falls area north to Omaha. Am I missing something here guys? Why the significant change in wording?

 

[Billy Griffin]

Why the significant change in wording?

Most likely; SPC is just playing this hour by hour by checking model runs, incoming data, etc.
Daytime shift came on as well. Lead forecasters will be a bit cautious with their wording with this potential event still 24 hours out.

I would expect a much more defined emphasis (and accompanied text) by early tomorrow morning.

Two distinct areas show the 'potential' for a very busy day tomorrow; the Wichita to OKC area and the eastern NE area as indicated by SPC's outlook.
I'm not particularly sold on the northern target due to the potential for instability to be lacking.
Same old scenario, really... do you play the southern instability or northern better shear? The northern target will likely be more clustered, but still will produce tornadoes. The more discrete stuff will play out in central Kansas through northern Texas.

Lots of potential tomorrow. Sure wish I was there! Good luck to all and... be safe.