10/01/09 FCST: NE/KS/OK/TX/MO

[Jim Bishop]

The 12z Sept 28 WRF shows hope for central to eastern Oklahoma. It only drives the cold front through northwestern Oklahoma by 00z and mixes a dryline to near the I-35 corridor or just to the west. The 500mb flow is quite veered to the west-southwest over all of Oklahoma between 60 & 70 knots. Beneath that is a 35-40 knot 850mb jut out of the southwest to south-southwest with southerly surface winds.

The veered 60+knot 500mb winds pretty much makes the entire 6km shear vetor quite good for discrete supercells. And it's very encouraging that the cold front will still be way up in northwestern Oklahoma at 00z, allowing a dryline to initate storms (according to the WRF).

Dewpoints are forecast to be in the mid 60s owing to sufficient instability, though nothing beyond 1500 CAPE as the 500mb temps look somewhat warm.

This "model trend" is something to monitor as it presents the potential for a more widespread severe weather event across parts of central and eastern Oklahoma, including the possibilities of tornadoes.

Of course the GFS (from last night) drives the cold front through OKC and Tulsa by 00z and is much more suggestive of a squall line. The European (from last night) generally agrees with the GFS solution. We'll have to see if these models follow the WRF trends. I doubt they will, but you never know.

 

[cdcollura]

Good day all,

I have no problems taking Wednesday and Thursday off this week, and given that I have 2 free tickets (I WAS saving those for hurricane chases), I'll probably roll the dice and play "whatever" happens in the central US Wednesday (9-30) and Thursday (10-1).

You might want to pay attention to a good setup for LP storms in W kansas on Wednesday if moisture returns fast enough. Thursday has much of a chance of being a squall line IF the front pushes through too fast. I like the higher instability on central OK for Thursday (10-1).

 

[Greg Blumberg]

Four midterms later, I finally get a chance to do some serious forecasting for this setup.

I'm actually feeling quite good about the moisture for either day. Every model, with the only exception being the 12z WRF cuts off today's cold front's push to the GOM/TX/AR intersection. They leave a nice pool of 60s Tds near the coast up to Austin with 70s right behind it.

I'm not even going to mention the 18z NAM run. It's really bringing in the trough like it's made of molasses. Based on the GFS and WRF, I'm liking Wednesday. The dynamics are there along with a fair amount of CAPE. I'm having trouble justifying the thermodynamics that the models are putting out for each day, so I will avoid discussing those. After this cold front in TX has something happening to it, I'll begin figuring out thermodynamics. I'm willing to bet that tonights runs will start bringing things together. I do agree with Chris about LPs in Kansas. I would love a fall chase of LPs in Kansas. Who cares about tornadoes, etc. After this ridge-y spring, I want structure shots.

Just wanted to add this, when you mention the time of the day, since the chase day has not centered on either day, make sure you mention the day in your discussion. I'm getting a headache just trying to figure what everyone is saying.

 

[cdcollura]

Good day all,

This morning (Monday AM) I had it all planned, fly into KC Tuesday night, return Friday AM - Expecting Wed to be 'the day before the day'. I just looked at some models and right now it does not look good for a Kansas chase as it did 12 hours ago.

The GFS has the surface low is in W Kansas on Wednesday (9/30), then way up in the Dakotas on late Thursday (10/1) with NW flow half way across TX. I know this is the GFS, and handles things a bit fast, but another concern is that winds are NW (or have a N component) ATTM and the Gulf is shut down, and will be until at least Tuesday evening, so moisture return for Wednesday's high-shear setup may not be sufficient.

Right now, my plans are on hold to go out there (I even cancelled my refundable tickets) ... I'll wait until tomorrow morning for a final thought. In my own opinion, I see the front surging before any hint of a dryline, with the "widespread" outbreak SPC is depicting being a damaging squall line / derecho type storm mode, mainly overnight on Thursday, when the LLJ is maximized.

 

[jamesmseitz]

A Chasers October Fest

I just looks a the models as well. If it holds this good be a descent day. The Jet seems to be in a Good place for this as well. Still worried about moisture as well as heating might not be as strong being this time of year. Still looks good right now and will be watching closely. I could handle one more chase to tide me over til next spring

 

[CZandbergen]

Based on the 0Z NAM and GFS runs for 10-1 I think this is a linear system as far as storm mode goes and it is going to be east of I-35. The bad news is the models seem to be moving toward the accelerated solution. Things may improve tomorrow, but the negative trend seems to be holding. This is unfortunate, but it is what it is. Looks like this is going to happen after dark and not be discreet. that and it will be in really poor chasing territory, at least in OK and to the south and east.

Darn...

 

[Chad Cowan]

Most likely a big time wind threat but there is a conditional tornado threat given that storm mode isn't squally. There isn't much doubt in my mind that this will be a MDT somewhere. We're only three days away from the event but the GFS and NAM are still in big time disagreement with the forward speed of the system. I can't chase but if I were I would be rooting for the NAM's sfc feature placements to win out. This would keep things in better terrain and leave room for redevelopment around the KS/MO border behind the early morning squall line before it brings the CF through. If the GFS's more progressive solution wins out I would chase further north into IA and nestle up next to the occluding surface low.

Pretty sad that this is the best system we've seen in > four months.

 

[Gabe Garfield]

The primary question for this potential chase day is "Will the short wave be favorably timed?" Unfortunately, it's going to be pretty tough, given that the wave will be zipping along at a good clip (short wavelength waves propagate faster). Right now, things look unfavorably timed: the wave moves over the warm sector on Thursday morning. However, there is some suggestion from the latest Euro that the wave will move onto the Plains a bit slower than previous progs suggested. If such is the case, there is a considerable risk of a significant severe weather event -- including tornadoes -- given the robust moisture return and strong wind shear. We shall see...

 

[Michael O'Keeffe]

Lets hope the ole reliable 6z NAM is on to something because it looks very interesting! It really slows the dryline/cold front keeping it in C KS/OK/SC NE most of the day until after dark allowing CAPE over 2000j/kg to develop and it allows strong SE surface winds across C/E KS/SC NE. If this model run is trending something which I think it is based on last night's run and the day before's run I think this may in fact verify and we could have more supercells than a squall line! It is nice to see a crappy setup look better and better instead of a good setup look crappier and crappier which has been typical this season.

 

[Jim Bishop]

I continue to be impressed by the WRF. The trend from yesterday continues and we may have a big day across eastern Kansas and western Missouri.

It mixes a dryline across western and central Oklahoma. The cold front moves southeastward across western to central Kansas, but just ahead of it is a pre-front trough oriented north south. So the two focus mechanisms for storm initiation appear to be a dryline across central to eastern Oklahoma and pre-frontal trough over central/eastern Kansas.

The warm sector is characterized by very fast 500mb flow with a slightly backed strong 850mb jet and slightly backed surface winds. If everything comes together just right there should be elongated supercells with a moderate to high tornado potential for a relatively short period of time before the cold front surges east and south and turns the whole thing into a raging squall line.

The GFS, however, surges the cold front south and east much faster and suggests a pure squall line. So maybe a compromise b/w the GFS and WRF is the correct solution. Should the WRF be correct, supercells and tornadoes would be much longer lived across eastern Kansas into Missouri.

 

[jamesmseitz]

Looking at everything this morning I think the main threat will be winds as Chad Cowan stated. I still hold that there will be a hour mabey 2 where things will be good. I am thinking Kansas right now. There seems to be a short time frame that the dry line will be ahead of everything. The shear will be good I still not sold on Moisture but after what happen here in the Twin Cities earlier this year if shear is great temp and moisture do not stop it....With that said it is still probably the last good chance til next year.

 

[CZandbergen]

As someone else mentioned, timing seems to be everything with this system. Based on the 06Z runs you have the NAM and WRF slowing things down and trying to setup a dryline play in central to eastern OK around 21Z on 10-1 but the GFS and the ECMWF have the system about 150 miles to the east pushing into AR by that point. I don't see enough agreement in the models to make a call on storm mode at this point. If and that is a big if, the NAM/WRF solution verifies you will have a short time for a sup play in central to eastern OK/KS. If the GFS/ECMWF verify it looks like a wind event in far eastern OK propagating to SE overnight.

Hopefully the models will sort themselves out later today/tonight.

 

[Mike Smith]

If one were to accept the 12Z NAM from today as a "perfect prog" there is a fairly good window of opportunity from EWK to PNC to IWX to 25 NNE of CNU back to EWK late afternoon until mid-evening Thursday.

 

[Jeff Piotrowski]

The new 12Z WRF!!

I like the trends with the DL now in Central KS/OK around 21Z. The main 500 mb wave has slowed a little.

The area across SE-NE near triple point all the way down to SC-OK ahead of the DL. The models have 2000 capes from NE-KS down to SC-OK.

The best cross over winds at 850 & 500 looks best across Eastern KS-OK.

SE-NE/SW-IA I would expect early low topped storms and tornados by 19Z a head of triple point and WF near OMA.

Kansas as cooling at mid levels and strong convergence on both the CF merges with DL near ICT around 21Z. Expect explosive development across Eastern KS back build into NE OK by 0Z. I would expect a few significant tornados in this area. Risk threat IE Moderate likely or high is possible.

The other prime area is SE-OK and western AR after 0Z this area could also have significant tornados near and after dark.

It also appears Oct 3-5 will be very active with significant outbreaks of SVR weather in the southern plains.

 

[W. Grant Dade]

I am really liking the area out ahead of the progged surface low, SE NE, SW IA, E KS, NW MO. Nice theta-e axis moving into an area of high 0-1km SRH.

Of course that is too far for me as I am working this week. So for a local chase I will probably head out to the OK TX line north of Dallas and play the dryline into southcentral OK.