09/10/10 FCST: IA, NE, MO, KS, MN

[Jeff Duda]

There looks to be a small region in the four-states area of SW IA, SE NE, NE KS, and NW MO where good instability and shear will come together Friday evening for a potential severe weather event. Looks like a shortwave with two different surface features: a meridionally oriented trough across the Dakotas and south into Nebraska and a broad low/trough in KS. A warm front will be draped WNWly to ESEly across S NE through C MO earlier in the day, gradually lifting north as the trough moves east. This boundary will delineate the good thermodynamic environment, as there will be minimal-no SBCAPE north of this boundary. Unfortunately, as is typical with many early or late season events, the best shear is mostly displaced from the sufficient instability. Thus, the shear in the area will not be as good as further north, but the 12Z WRF-NMM is suggesting that there will be > 150 m2/s2 0-1 km SRH in SW IA and NW MO as well as 200 - 300 or more m2/s2 0 - 3 km SRH extending north and NEWD from as far south as NE KS. Thus the potential for rotating storms is certainly non-zero, but how high it will go certainly depends on how much overlap there will be between the instability axis and the shear axis. The farther north the warm front makes it may result in a larger area (assuming the upper level features don't also move farther north, which is probably what would happen).

On a final note, of course there will be some capping issues, but it doesn't look nearly as bad as Monday's event did. The 12Z NAM lid strength index is negative in the area at 00, and both American models are showing precip at 00Z.

I added MN to the list because of the likelihood of elevated instability and convection there, too. With very good shear in that area, there could be some elevated hailers.

 

[Mark Blue]

We're planning to chase this setup as well as long as it still looks as good on Friday morning as it does now. I've been looking at the parameters and like some of what I see, especially in the area where NE, KS, IA and MO meet along the lower Missouri River Valley. There appears to be 40 to as much as 50 knots of bulk shear from the surface to 500 mb in that general area. The surface winds are backed to almost due east in NW MO at 0Z Saturday (Friday night 6 pm), with winds out of the SSW at 850 mb, and eventually SW at 500 mb, so very nice turning with height. The 18Z NAM has CAPE as high as 3000 J/kg slightly to the south down into eastern KS - so I'm not sure if that is overdone - but there appears to be plenty of moisture at the surface with low 70 dewpoints co-located with the CAPE. EHI is looking very healthy in the same area as the CAPE and moisture, so there is some indication that the shear and instability may be in the same general area - hopefully not too far south though. SRH with values close to what Jeff mentioned run from NE KS due east along the warm front into northern MO. What pulls it altogether for me is the below hodograph that has nice curvature and plenty of lift just north of the warm front where I think the action will be Friday at show time. It's a little further north than the other parameters mentioned above, but perhaps if the warm front is lifting north during the day and early evening that would be the best play for surface based storm initiation with the best helicity. It's for Clarinda in SW IA (click 60 hour box for 0Z Saturday):

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=NAM&STATIONID=kicl

The LFCs are a bit high on the Skew T readout, so I can only hope that comes down with time. Several other reporting stations in that general area had decent looking Skew-Ts and hodographs, but none as good as Clarinda. Some I looked at were: Nebraska City (KAFK), Beatrice (KBIE), Topeka (KTOP), and Falls City (KFNB). Right now our target would be St Joseph MO where we can adjust in any direction as things develop. I sure hope it pans out as this is a long haul from Denver for a one day chase.

 

[Mike Smith]

Friday is shaping up to be an interesting day. SPC has raised its day two probabilities to 30% in NE KS.

While I think NE KS will be in play, I am interested in a triangular area from P28 to BVO to 25 N. of EMP.

The high res. model is forecasting a low near P28 at both 4 and 7pm tomorrow with increasing WAA and moisture advection. Heights fall nicely with decent flow at 500 mb and above. The NAM is forecasting 3000+j over most of this area at 4pm. There is a weak boundary across the area of interest to focus convergence and keep surface winds adequately backed.

What is lacking is 850mb flow. If that can correct itself, and I think it can, we could have a couple of tornadoes in the outlined area.

 

[Lanny Dean]

Friday is shaping up to be an interesting day. SPC has raised its day two probabilities to 30% in NE KS.

While I think NE KS will be in play, I am interested in a triangular area from P28 to BVO to 25 N. of EMP.

The high res. model is forecasting a low near P28 at both 4 and 7pm tomorrow with increasing WAA and moisture advection. Heights fall nicely with decent flow at 500 mb and above. The NAM is forecasting 3000+j over most of this area at 4pm. There is a weak boundary across the area of interest to focus convergence and keep surface winds adequately backed.
What is lacking is 850mb flow. If that can correct itself, and I think it can, we could have a couple of tornadoes in the outlined area.

It was interesting to see everyone playing up the northern end of this possible event and I was kinda hoping it would stay that way!

I saw the "broad" low near Med. Lodge (P28) as well as the boundry and via the 00z run it looks as though 850 winds may turn south just east of these features. 3,000-3500j/kg with -7 plus LIs....I think this area could be a pretty decent play. Set up kinda reminds me of May 13 2009 event!

Certainly something to keep an eye on

 

[Brian Davidson]

I'm going to take a crack at a prediction here, so If I'm wrong please tell me; I'm still new at this!

I'm looking at the RUC model at 6, 8, and 9+ hours. Its showing the CAPE at being 5500+. It looks like Ottawa, Ks will be at the heart of it. Again, please prove me wrong and tell me why I'm wrong. I want to learn!
**EDIT**
Took out the model for CAPE due to it updating
***

I'm also predicting the biggest of the action will start around 8pm and go till midnight CST and just storms after.

 

[rdale]

Its showing the CAPE at being 5500+. It looks like Ottawa, Ks will be at the heart of it.

If the RUC CAPE map was all you needed for severe weather forecasting, your analysis is perfect. But as mentioned above, there are other ingredients that may not be there. You might take a peek at the educational section here for more forecasting aids.

I'm also predicting the biggest of the action will start around 8pm and go till midnight CST and just storms after.

The US is on Daylight Saving Time now, so I think you mean CDT?

 

[Jonathan Whitehead]

I posted a quick blog on my page found in my sig.

Ill summarize what I said by noting that with the main upper energy being removed into NE, not expecting huge supercell event, mostly multicell clusters due to the weak flow but areas closer to the sfc low in NERN KS will have the best combination of instability and low level shear juxtoposed over their area, so thats where Id like for risk of isolated tornadoes.