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

[Rocky Rascovich]

It seems pretty evident with the overall consistency of the ensembles and the the EURO and GFS models that we will be entering an active period of convective weather across the central and southern plains.

The first system of note according to the 0Z and 6Z runs suggests cyclogenesis occurring across W.KS with troughing extending SW into the TX PH. early on Thurs. 1 Oct. This initial system will advect a fair amount of moisture based on the projected PWATS across the region. Timing will be critical with this as based on the models, the best dynamics may come through the I-35 corridor to early in the day to utilize day time heating. Capes will be marginal but shear parameters look more than sufficent for severe storms if they can remain isolated.

Predominate storm type though, will likely be a fast moving squall line due to the progressive nature of this system and strong vertical velocities accompanying it. As of now, it looks as though areas from EMP on down to PNC over to TUL and on down to MLC may be under the gun for SVR potential. Of course, alot can happen with the models tweeking on the timing of this. My guess is that this may slow a tad and the highest risk area could be displaced to the west.. we'll see.

Beyond that, it looks as though we'll have more potential systems to deal with but that will be for a later thread.

Cheers!

 

[Jim Bishop]

I couldn't agree more that we are about to enter an active severe weather period over the southern to central Plains beginning Wed or Thur.

Right now it's difficult to speak in detail about specific days because the operational models (GFS and European) disagree on the timing, strength and exact location of the initial shortwave ejecting on Thur. For example, the 12z GFS for Thur would suggest an environment characterized by high shear fit for fast moving tornadic supercells with ample low level moisture and sufficient CAPE over central Kansas into southern Nebraska. Unfortunately the European Operational and both ensembles suggest the cold front will surge south and east much faster and indicate a more squall line like scenario. So uncertainty is quite high on the storm mode at this time, but the potential for severe storms is high.

It appears the next good opportunity for organized severe storms would come Sun and Mon over the southern Plains with the next shortwave. These two days could be quite interesting since they will have an even better supply of deep, low level moisture.

If a couple days end up looking really good, especially into the weekend I'm going to need to find some cheap airfare!

 

[Rocky Rascovich]

I was apprehensive in discussing further about the following weekend due to the time constraints this forum allows on the FCST topics.. but, if the 12Z GFS data comes to pass, the following weekend does have a much better set up and actually looks down right scary. The only reason why surely I can't see it being as bad as the models suggests is due to climatology for this time of year, and of course, we're talking over a week away. Who knows what flips and turns the models will do between now and then.

Concerning the latest data, It does look as though the system may slow down a smidge for Thursday 1 Oct. I am concerned about the potential for the frontal surge undercutting what potentially severe storms that may occur. At least if anything does occur, it will hit at peak heating times, adding a little bit of cape to the brew, not to mention that I'll have a better chance of chasing as I'm off work by 4:30. Still, this will be fascinating to watch this evolve as we near the date of a fall chase.

I was just thinking (which for me could be dangerous) We haven't had a decent fall season in how long? The last one was in '98 right? Didn't we have a budding el nino event that year too?

 

[Jim Bishop]

I was just thinking (which for me could be dangerous) We haven't had a decent fall season in how long? The last one was in '98 right? Didn't we have a budding el nino event that year too?

In the fall of 1998 we were in a moderate La Nina. But what's interesting about the weather pattern we are going into for the next 15 days, possibly longer, is it's actually indicative of La Nina like pattern, despite the fact that we are in a weak (nearly low end moderate) El Nino. So take that for what's i worth. Although the 30 day running average of the SOI (Southern Oscillation Index) has been positive since Sept 16, which is indicative of a La Nina like pattern.

Going a step further, I looked looked at the monthly temperature anomalies for October, 1998. The month feature below normal temperatures over the western half of the U.S. (cool troughing) and above normal temperatures over much of the central to eastern U.S. (broad ridging). Interesting because that broadly fits what I'm been expecting for October, but it's not one of my analogs.

 

[David Reimer]

Comparing this morning's 12Z NAM and GFS at Hour 84, the NAM is much slower bringing the system in, which is not a surprise considering the GFS is usually too fast with a system. That's why Im not really that worried with this run, even though it shows the cold front around Dallas by 0Z Friday. I'd just take it as a bad run.

 

[Andrew Stoller]

I know it's early to get picky about specifics, but run after run of both the GFS and now the NAM is showing a stout elevated mixed layer/capping in the warm sector.

 

[Derek Weston]

I know it's early to get picky about specifics, but run after run of both the GFS and now the NAM is showing a stout elevated mixed layer/capping in the warm sector.

Less than impressed with CAPE as well.

 

[David Reimer]

Less than impressed with CAPE as well.

Not knowing what area your talking about, I'd say that Southern Oklahoma to Northern Texas are looking the best at the moment where the highest amounts of CAPE are projected to be by the GFS.

 

[Derek Weston]

Not knowing what area your talking about, I'd say that Southern Oklahoma to Northern Texas are looking the best at the moment where the highest amounts of CAPE are projected to be by the GFS.

See that now. Messed up and looked at the wrong day. Yeah, CAPE not too bad on the 1st down in Texas. (per 12z GFS) Of course, badly veered low level flow doesn't look too good... big forcing along the CF... mode doesn't look good. We'll see the next few runs here though.

 

[Brandon Goforth]

Not knowing what area your talking about, I'd say that Southern Oklahoma to Northern Texas are looking the best at the moment where the highest amounts of CAPE are projected to be by the GFS.

Actually I think they are looking at Wednesday, rather than Thursday...the NAM doesn't even go out to Thursday afternoon yet as Andrew commented on. Yeah, 2500 CAPE will get it done, but the GFS seems a bit fast, pushing the cold front to DFW by 0Z and looking linear. When compared to the NAM 84 hours out, the NAM is quite a bit slower. I'm not going to look too much into it until I can check out the 12Z NAM tomorrow, but we need the slower solution if you want anything worth chasing.

 

[Brett Roberts]

Timing, timing, timing. We've still got several days of model flip-flopping to get through, but in the grand scheme of things, it seems like they're slowly converging on a solution that brings the best dynamics through the Plains overnight Wednesday into Thursday morning. I guess we should have seen this coming, being that the ECMWF and GFS each showed great chase setups several days ago, but disagreed on which day it would be! (Thursday vs. Wednesday)

Aside from the likely-unfortunate timing of the trough ejecting into the Plains, another thing that's changed on the models is the position of the downstream trough along the east coast. Earlier this week when the GFS was showing an apocalyptic setup, it had the downstream trough axis over the Canadian Maritimes. Now, the models are all showing it over New York. I'd be curious to see how many good chase days have occurred in such a short-wavelength pattern, with another trough so close by to the east.

The 00z NAM this evening indicates the trough axis for "our" system still hanging back along the UT/CO border at 12z Thursday. This makes me think that the most realistic alternative to the disastrously ill-timed 12z GFS (which seems to be nearly the worst-case scenario) is a slower solution that sets up an I-35 chase Thursday afternoon, as opposed to a faster one that allows for a breakable cap Wednesday.

 

[Bart_Comstock]

Actually I think they are looking at Wednesday, rather than Thursday...the NAM doesn't even go out to Thursday afternoon yet as Andrew commented on. Yeah, 2500 CAPE will get it done, but the GFS seems a bit fast, pushing the cold front to DFW by 0Z and looking linear. When compared to the NAM 84 hours out, the NAM is quite a bit slower. I'm not going to look too much into it until I can check out the 12Z NAM tomorrow, but we need the slower solution if you want anything worth chasing.

They are talking about on the previous run of the GFS:

I really do hope that the current run of the GFS is bogus as it doesn't look promising at all for Thursday. Wednesday is starting to look so-so but the lack of CAPE and decent moisture will serve to most likely prevent that day from being anything worth even mentioning. All in all I am starting to get my doubts for this event.
http://img199.imageshack.us/img199/8750/gfsus0mlcape120.gifhttp://img199.imageshack.us/img199/8750/gfsus0mlcape120.gif

 

[Andrew Ryan]

The wind profile has improved from last night. I think the moisture is bit overdone but it still looks good. But yikes, the 0z GFS is still pushing the cold front thru really quickly. I hope it slows done a bit, which it probably will do, otherwise it will just be a squall line or the main event will be confined to the eastern areas of OK/TX.

 

[Bart_Comstock]

The wind profile has improved from last night. I think the moisture is bit overdone but it still looks good. But yikes, the 0z GFS is still pushing the cold front thru really quickly. I hope it slows done a bit, which it probably will do, otherwise it will just be a squall line or the main event will be confined to the eastern areas of OK/TX.

I may be desperate this time of the year but I'm not so desperate to try and pull another Jungle chase. If anything I'll park in the southern part of KNWA's local viewing area and chase there. One good thing about the GFS is it consistently does show systems moving through much faster than they actually will. Come day 3 I suspect the models will drop the event or back off considerably on it then on day 2 it will show back up and look decent once more. As long as the SPC doesn't jinx us with their usage of the word outbreak from today's out look we should be alright but I still don't think this will be by any means a apocalyptic spring like system. It is a bit scary to look at the GFS and see the front just east of I-44 at 0z Fri and then at 6z see it halfway across Arkansas.
Wednesday is looking slightly better and could possibly yield a photogenic storm or two in western Kansas.

 

[Brandon Goforth]

Well, the 12Z NAM is out and it is only slightly slower. I'm really not liking this setup very much at all at this point. That thing is shoving through pretty quickly, but even worse, I hate the badly veering 850s that both the NAM and GFS are strongly agreeing on. This looks more like a raging squall line at this point that will quickly get into unchaseable terrain as it moves east of I-35.