4/25/09 FCST: NE/KS/OK/TX

[Eric Bucsela]

The NAM is stronger with the main wave and brings it to the western Hi Plains about 18 hr later than the GFS. The strong wave is why the front pulls north so dramatically. If this verifies, Sunday would indeed be the better day (assuming convective debris etc doesn't complicate things).

I agree with Matt (thanks for taking a deep breath here!) that much better-looking setups have gone bad this far in advance, but here's hoping Sat is still good and the NAM is too slow. I think (at least on longer time-scales) the GFS can be a bit too progressive.

 

[Connor McCrorey]

I still don't believe the NAM, but it has been very consistent. My forecast on the www.texasstormchasers.com blog still stands, and I'm thinking NW OK is the place to be. I'll post again later tonight, after the 0z runs are out.

 

[Adam Penney]

I am a little concerned about the such weak upper level winds progged at 0Z Sunday. Both the 500mb and 850mb winds are pretty weak, and are not condusive for a major tornado threat.

ATTM, it looks like an isolated tornado threat to me.

 

[jamesmseitz]

I am not happy about the lastest run (GFS). It shows no good mixing on Saturday at all. Everything is Sunday. Even SREF has the theat deminished quite a bit. Sunday seems to be the only day now. After years of this I should be used to this waffleing but it always confuses the heck out of me. Well going to bed now.... See what the morning brings.

 

[Derek Weston]

I am a little concerned about the such weak upper level winds progged at 0Z Sunday. Both the 500mb and 850mb winds are pretty weak, and are not condusive for a major tornado threat.

ATTM, it looks like an isolated tornado threat to me.

This has been a concern for a while -- upwards of a week ago the GFS was basically latching onto the same situation... energy from the trough perhaps being too far back to sync up with low level shear and good CAPE.

However, lately, things have been looking more positive in this regard... especially on Sunday in the southern plains. Saturday still looked like it had a shot too down there.

And... guys... get a look at the latest 0z GFS? Has come to agreement with the NAM about the crashing cold-front on Saturday. (in fact, last two GFS runs agreed) Appears the NAM isn't that crazy afterall.

 

[Adam Penney]

And... guys... get a look at the latest 0z GFS? Has come to agreement with the NAM about the crashing cold-front on Saturday. (in fact, last two GFS runs agreed) Appears the NAM isn't that crazy afterall.

I still feel there are some pretty significant differences between the two. The appears to be atleast 100 miles difference in the placement of the cold front. The GFS has the greatest SBCAPE AOA 2500-3000 j/kg near the ICT-Medicine Lodge area at 0Z. The NAM continues to take it into SW Oklahoma near I-40 and southward.

Still seems to be a pretty big difference to me.

 

[Mike Hollingshead]

This has been a concern for a while -- upwards of a week ago the GFS was basically latching onto the same situation... energy from the trough perhaps being too far back to sync up with low level shear and good CAPE.

However, lately, things have been looking more positive in this regard... especially on Sunday in the southern plains. Saturday still looked like it had a shot too down there.

And... guys... get a look at the latest 0z GFS? Has come to agreement with the NAM about the crashing cold-front on Saturday. (in fact, last two GFS runs agreed) Appears the NAM isn't that crazy afterall.

The 0z GFS is still a good bit north of what the NAM is saying with the cold front. By Sunday evening the differences between the models remains what it has been...night and day(I realize that is a different day).

http://www.rap.ucar.edu/weather/model/eta72hr_500_wnd.gif

http://www.rap.ucar.edu/weather/model/gfs072hr_500_wnd.gif

That aspect of this is getting quite annoying to me. That is where the GFS has had the support of the other models.

As far as Saturday is concerned, to me it's one of those just on the verge of nice, or should I say nice enough to be capable of producing a great supercell or two. Combine how Saturday looks with the big fat differences by Sunday it makes deciding to chase Saturday from very far rather tough. This whole scenario is reminding me why it's pretty stupid to look at things terribly hard this far out, lol, yet I never learn. Saturday to me has the cold front question and the potential later initiation question, as well as flow. Sunday has the massive difference in the speed of the trough ejecting but either solution the TX panhandle could work...so that argues to just be there both days anyway if you have to drive very far. Arrgh.

 

[Brett Roberts]

I still feel there are some pretty significant differences between the two. The appears to be atleast 100 miles difference in the placement of the cold front. The GFS has the greatest SBCAPE AOA 2500-3000 j/kg near the ICT-Medicine Lodge area at 0Z. The NAM continues to take it into SW Oklahoma near I-40 and southward.

Still seems to be a pretty big difference to me.

I was thinking the same thing. The GFS looks to maintain a noticeably more favorable scenario for Saturday than the NAM on tonight's runs. The cold front does push southward during the day on both models, but slows down or even becomes stationary by mid-afternoon on the GFS. Additionally, the GFS continues to depict a slightly stronger surface low, resulting in somewhat better low-level winds; a sampling of forecast soundings around W OK reveals nice 0-1 km SRH on the GFS, with more marginal values on the NAM.

Of course, the caveat is that the GFS has undoubtedly been trending towards the less-appealing NAM solution, which is definitely cause for concern.

The modest flow at and above 500 mb has been shown on the models all along, and is not going to keep me home Saturday. I know it gets tiring when people throw out "analog" days just to justify their excitement, but I think one look at 2004-05-12 should be sufficient reminder that good chase days can be had even with weak mid-level flow and a southward-moving cold front. Needless to say, there are probably 10 other historical chase days that looked vaguely similar to Saturday and busted, but given that it's a) the weekend and b) the first high-CAPE setup of 2009, it will take a lot worse than tonight's runs to convince me it's not worth chasing. A classic, memorable dryline outbreak would be nice, but even an isolated triple-point threat with 65 F Td's and 2500+ CAPE is still better than anything we've seen on the Plains since last June.

 

[Connor McCrorey]

Just because the speed shear on this system isn't as high as the speed shear on every early season setup we've seen, it's an isolated tornado threat? I have to disagree. Hodographs for W OK look great from what I have seen. I still think both days this weekend have excellent potential, no matter which model wins out.

I just posted an updated forecast on the www.texasstormchasers.com blog. The exact post is at http://blog.texasstormchasers.com/?q=node/4.

 

[Derek Weston]

The 0z GFS is still a good bit north of what the NAM is saying with the cold front. By Sunday evening the differences between the models remains what it has been...night and day.

http://www.rap.ucar.edu/weather/model/eta72hr_500_wnd.gif

http://www.rap.ucar.edu/weather/model/gfs072hr_500_wnd.gif

That aspect of this is getting quite annoying to me. That is where the GFS has had the support of the other models.

As far as Saturday is concerned, to me it's one of those just on the verge of nice, or should I say nice enough to be capable of producing a great supercell or two. Combine how Saturday looks with the big fat differences by Sunday it makes deciding to chase Saturday from very far rather tough. This whole scenario is reminding me why it's pretty stupid to look at things terribly hard this far out, lol, yet I never learn. Saturday to me has the cold front question and the potential later initiation question, as well as flow. Sunday has the massive difference in the speed of the trough ejecting but either solution the TX panhandle could work...so that argues to just be there both days anyway if you have to drive very far. Arrgh.

ah, well, wasn't looking as closely I guess. I had been glancing at the surface map initially, and for a while with the GFS...midwest wasn't hit that hard by the CF on Saturday... NAM had been wiping it out -- and then GFS agreed... and made my comment right after seeing that. (and the NAM does bring it along further, Adam)

I agree, either solution provides a play down south on Sunday... N TX/OK panhandle area both days. (well, a little east of that Saturday)

(personally, if I were anywhere halfway close to the TX panhandle, I'd be there Sunday -- and if I was going out on the weekend... hey, I'll take a shot at Saturday too...despite all the concerns outlined... I think Mr. Roberts makes a good point)

 

[Greg McLaughlin]

Just because the speed shear on this system isn't as high as the speed shear on every early season setup we've seen, it's an isolated tornado threat? I have to disagree. Hodographs for W OK look great from what I have seen. I still think both days this weekend have excellent potential, no matter which model wins out.

I just posted an updated forecast on the www.texasstormchasers.com blog. The exact post is at http://blog.texasstormchasers.com/?q=node/4.

I agree with you Connor. All of my best tornadoes have come on days when H5 winds were 45kts or less. I got a peak at the Clinton, OK sounding (kclk) valid at 00Z SUN (per NAM) and I really liked what I saw. I think Saturday has a lot of potential, albeit on a more isolated basis. If the NAM is correct (which I am starting to wonder if its on to something now) then SUN could be big if the warm sector isnt a wash. Its a wait and see situation. I noticed DDC in their discussion this morning said they felt the NAM was handling the cold front better than the other models....based on past experience with cold fronts under a southwest flow regime.

 

[Shane Adams]

Anyone else wanna start making side bets as to how many times an approaching system will go from "the biggest event of the year" to "not worth the drive"? We can make the powerball a bet to see what overall %age of naysayers end up chasing anyway.

 

[Warren Faidley]

Its been my experience that relying on the models for pinpoint surface specifics more than 24 hours out can drive you crazy -- or lead to a longer than necessary drive. In ancient chase times we would jokingly (friendly) call such forecasting "sorcery." Regardless, the key elements will be present somewhere in the next 48 hours+ and there will be severe weather this weekend and likely tornadoes in the Plains. I would not be surprised to see at least one above slight risk potential in the next few days. If we knew for certain how and where everything was going to happen....... it would not be any fun!

W.

In Alamogordo, NM heading east today.

 

[Andrew Ryan]

The 12z GFS hasn't come out yet, but the 12z NAM definitely makes Sunday "The Day." NAM has slowed down the progress of the trough, just a bit. Have to wait and see what the GFS has to say.

 

[Mike Peregrine]

After looking at the 12z runs, I'm happy with a southwestern Oklahoma target for tomorrow, and won't be moving far to reposition for Sunday. Parameters look good enough to me tomorrow to warrant a drive, especially just to get into position for Sunday, if nothing else. SigTor has a bullseye on the state line with the TX panhandle, with fcst ML CAPE in the >3000 J/kg range. Scott and I will likely head down to this area tonight after work to get into position. It's worth it for a 'day before the day' situation, IMO.