5/15/09 FCST: IL/IA/MO/KS/OK

[Ryan Wichman]

No time to rest from yesterday's storms as it looks like another favorable set up for some tornadic supercells on Friday. Not as dynamic of a set up as this last system, but still looks to hold a lot of potential.

Here in IL, a warm front looks to move northward on Friday allowing the instability to increase from MO edging into IL and IA. Some morning convection looks to agian lay down some OFB's or the warm front itself could be a play with nice directional shear. Looks like the same area's which were hit Wednesday could be under the gun agian tomorrow.

 

[Jacob Ferden]

FWIW (after I sat at home yesterday), the GFS seems to be much more in favor of a good environment than the NAM over northern Oklahoma and southern Kansas. The lower CAPE values suggested by the NAM (1500-2000 j/kg) make me suspect that we will see initiation hold off until near or after dark, when the cap is weaker. Of course, a lot can change, but it's difficult for me to get too revved up over the instability after we saw much higher CAPE values on Wednesday. But we'll see.

 

[Brian Stertz]

Just not seeing much LLJ inflow to keep things from gusting out looking at the 12z stuff. May have some brief pulse type circulations but just not much in way of ideal sustained tornadic conditions tomorrow. Had planned to chase but not too excited with what I am seeing now.

 

[Bill Tabor]

NAM: Yep, definitely problems this day IMO with tornadoes - not severe storms. As Brian mentions the overall sfc wind field is weak. 18z decent strength winds through KS/OK, but at that time 850mb winds are veered along the sfc frontal boundary which encourages linear structures. Best lower level wind fields are in se KS and ne OK, but at 0z these winds are weak at sfc when 850mb winds are finally backed more. Additionally at 0z while the 700mb winds may be present in bare adequate amounts it is at this time in this region we are missing our good 500mb flow. The rest of the area E and N are in better mid to upper level jet flow, but are either north of the boundary or have no good lower level support for tornadoes.

Further west toward the sfc low in NM toward the convective time of 0z appears ATM that 700mb to 500mb flow is mostly absent limiting deep layer shear.

EDIT: Note my comments are in regards to the area south of Iowa.

 

[Derrick Herndon]

I think the only thing that may save tomorrow would be a favorable outflow boundary that sets up East/West across south central KS. Such a boundary might improve the low-level flow situation and if oriented with the storm motions might allow for something to be longer lived. The NAM shows the early convection that might set this up but the wind fields do not really show anything of interest in the low-levels. It is possible the model is just not handling the boundary layer flow over this area very well.

 

[Skip Talbot]

It looks like the best shear and instability combo is setting up over the same areas that were hit yesterday in NE MO. EHI values are spiking here where 3000 J/Kg SBCAPE is still catching the tail end of the trough and LLJ as it moves through. The main problem I see with this area is that there appears to be ongoing convection from the morning throughout the day in this area. The WRF is plotting precip all day along the boundary here. It might be tough to get something discrete with unadultered inflow.

 

[Andrew Pritchard]

Does look like another decent setup in the same general area. Unfortunately phasing is kind of weird with the best shear being ahead of the secondary low that will be over eastern Iowa and northwestern Illinois placing the best directional shear over western and central Illinois, but the higher cape values being back in Missouri.

I'd probably take my chances with the better shear ahead of the low and along the warm front, where ever that ends up being. Will be plenty of convection north of the warm front again, so I'd look for areas of clearing south of there for new surface based convection. I'd probably watch the Quincy, IL area tomorrow afternoon. Looks like decent cape building in there south of the boundary and still got good southerly surface flow ahead of the low. Right on the nose of the H5 jet streak too.

 

[Andrew Pritchard]

Here's to hoping the GFS verifies, I suppose. It really deepens that surface low right over NW Illinois at 0Z along the warm front, with a really tight instability gradient right along it with cape values approaching 3500 j/kg. If that thermodynamic profile and the deepening of the low really do happen along the warm front, I'd say any surface based convection that can develop on there should have no problem rotating.

Peoria area looks really good at 0z.

Setup like this isn't really easily forecasted however as it hinges on a lot of different variables, which the model discrepancies show, so we really won't know much until afternoon rolls around. Certainly bares watching through the day tomorrow though for those within a couple hours.

 

[Jeff Piotrowski]

Two great target areas for Friday Wichita KS-Perryton TX

The info below is what think 0Z 12KM & 4KM nam model is saying.

THE KEY FOR FRIDAY IS MORNING CONVETION AND THE OFB AND WHER IT SETS UP BY 21Z!!!!!

New 4KM nam has OFB /CF Kingman county KS 21Z 5000 capes EHI 6.
50+ 500 mb WNW flow. This is a window between 20-1Z for Significant tornados in KINGMAN, SEDWICK COUNTIES KS!!!!

Then the second area is Northern Lipscomb county TX 5000 cape with deep cape of 400 and EHI 5 at OZ. The 850 flow backs 170 and increase to 45knt's with 500mb WNW 45knt's WNW cross over will lead to long live tornado producing storms.

The entire DL pops from N TXPHNDL all the way down to Midland.

I would think an upgrade to moderate risk once the boundaries are in place by late morning.

Update: per 12Z data. With ongoing storms in NE KS OFB and CF will now be on West of KC at 21Z with tornado threat high in the KC metro area after 21Z. 12Z Ruc supports this solution also.

The CF storms will back build by 22z to NE TX PHDL but isolated in nature.

Ruc has capes over 6000 over SC KS ahead of front lots of big bad storms today.

 

[Brandon Sullivan]

Here's to hoping the GFS verifies, I suppose. It really deepens that surface low right over NW Illinois at 0Z along the warm front, with a really tight instability gradient right along it with cape values approaching 3500 j/kg. If that thermodynamic profile and the deepening of the low really do happen along the warm front, I'd say any surface based convection that can develop on there should have no problem rotating.

Peoria area looks really good at 0z.

Beat me to the punch.

Crazy how the NAM and GFS can differ soo much. I felt like the GFS really did the best on the convective setup for Wednesday, so we shall see what happens tomorrow.

Bout the only thinh I have to add is, the 3z RUC 12Hr FCST agrees with the 00z 15 HR GFS FCST as far as major synoptic details. Hmmm..

 

[Bill Schintler]

Chase Target for Friday, May 15

Chase target:
10 miles east of Spearman, TX (in the northeastern panhandle).

Timing and storm mode:
Supercell storms should develop at the triple point of a front and an advancing dry line after 3 PM CDT, with storm motion to the northeast at 10 mph. Additional isolated storms may form further south along the dry line in the panhandle of TX.

Synopsis:
A broad ULVL trough extended across the NCNTRL CONUS, with the strongest ULVL flow well N of TX and OK. In WRN TX, a retreating CF extended from near CDS to north of MAF. An isolated storm fired at the intersection of the front and a DL just N of MAF. Further N in the TX panhandle, moisture has increases dramatically over the last 18 hours, increasing from 30F this morning to the upper-50’s to low-60’s as seen in the latest observations. Fog and ST will develop over the ERN panhandle as SERLY upsloping flow increases moisture in this area.

Discussion:
Models indicate a strengthening SFC low W of AMA by 00Z, partially in response to strong SFC heating. A SFC trough will extend NE into the OK panhandle, separating air masses of similar temperature but with a sharp moisture gradient from N to S. ST and fog will persist in the ERN panhandle through midday, before moving east of the area while allowing for strong insolation. A dryline will mix eastward through the TX panhandle, and it is at the triple point of the dryline and trough where convergence should be strongest. Lift will increase as a shortwave emerges from NM. Orographic lift along the western Red River near the Caprock in the southeast panhandle, and the Canadian river, will locally enhance lift and backing of surface winds.

Strong instability will result as steep mid-level lapse rates AOA 8.5C/km overspreads a 100mb-deep moist layer with SFC dewpoints of 60-65F, resulting in an axis of SFC-90mb MLCAPEs in excess of 3000J/kg. This strong instability may somewhat offset marginal shear, with deep-layer shear AOB 40 kts. Shear should be locally higher over the panhandle as a compact H5 disturbance moves through the area between 21Z and 03Z. Tornado probability will increase after 00Z as LLVL directional shear increases with a strengthening LLJ and LCL levels decrease to 1200m AGL or less.

- Bill

12:09 AM CDT, 05/15/09

 

[Jeff Snyder]

I'm a bit leery of the small-scale mid-level wave that appears on the 24 hr NAM forecast valid tomorrow evening (00 UTC)... Associated with the small 500 mb jet streak is a distinct vorticity pair (look at the 500 mb vort forecast) and a QPF max. There are also 500 mb vort pairs associated with QPF maxima near ICT and LBB as well. I wonder if the model isn't adjusting for what's amounting to the release of strong to extreme instability. Such a jetlet doesn't appear to be continuous from 18z to 00z to 06z; it appears primarily only at 00z, which adds to my hesitation to treat it as a "real" feature and not an artifact of the model producing very high QPF. Granted, the operational NAM obviously cannot explicitly model convection, but I've seen cases similar to this before, when the model producing a very compact 500 mb jet streak nearly collocated with a 500 mb vorticity pair (a small local max adjacent to a small local min) and very high QPF. Note also the location of the 'off-the-chart' 500 mb UVV forecast valid for the same time, which are collocated with the QPF max and 500 mb vorticity 'couplets'. All of this together is telling me to treat that TX PH 500 mb local jet streak with significant caution. Maybe we'll see something on the TCC profiler tomorrow morning or early afternoon, but I have my suspicions that the particular 500 mb jet maxima forecast by the 00z NAM valid at 24 hrs isn't a 'real' feature that would exist without the intense convection/QPF the model is producing.

 

[Bill Hark]

Complicated forecast but definitely worth chasing before the pattern changes. I am not as enthusiastic about the potential decent chaseable and visible tornadoes but if I was out, I would chase this event. There is rather marginal 500 mb flow with the best in northern Kansas, MO and Il. Unfortunately, the 850 winds will be from the southwest. There maybe some backing of the surface winds in NE Kansas before the front sweeps through. Some chasers are targeting the southern Texas panhandle but I think the upper level winds will be too low despite some localized southeast winds with the low. The best compromise in good chase territory will be in the Hutchinson area and one would have to get on the storms early before they form a massive line and then the front arrives. There may be a better chance of tornadoes in northeastern MO with backing of the surface winds and good upper level flow but the area will be killed by the front. Forecast CAPE is not as good as farther southwest in Kansas. Macon, MO would be my first target if it wasn’t for the chase territory

Bill Hark

 

[John Farley]

Again today, like Wednesday, I have life-chasing conflict, as I have a graduation event tonight. If I had no restrictions, I would probably head to Columbia, MO, and watch from there. As it is, I will again stay near home and hope something pops near the STL area. If the RUC is right, I might be in business - it shows CAPE around 3000 in this area, with storms surging south into the area early in the afternoon. Weak wind fields, but good directional shear. If the NAM is right, we'll have only garden-variety thundershowers as happened Wednesday in this area. With all the precip now across northern MO, I would think the area of action will be a little farther south than Wednesday, though.

 

[Stephen Locke]

Initial decisions today based on terrain. The Kirksville storm Wednesday was a frustration of time and effort as I was forced to shoot it through trees and between hills. That's not a lesson I need to learn yet again today. I'm moving wsw out of KC today away fron the greatest tornado threat. I need open country to shoot my style of still photography.

I'd rather bust in Kansas then chase an obscured wedge along the Ho Chi Minh Trail.