4/1/10 FCST: TX/OK/KS/NE/SD/MN

[Brett Roberts]

With the ECMWF finally ceding ground to the progressive GFS solution last night, my focus is turning to Thursday, since the prospects for discrete, chaseable supercells Friday now seem iffy at best anywhere W of I-35.

Other than the typically impressive "day-before-the-day" warm sector hodographs, not much is ideal about Thursday's setup. Moisture return looks mediocre for early April, so overcoming the stout EML that will result from several days of SW mid-level flow should be challenging, to say the least. In fact, neither the GFS nor NAM break out any precipitation prior to 00z Fri on this morning's runs.

On the bright side, the 29/12z NAM indicates fairly deep moisture up to 850 mb along the dryline over NW TX, the E TX Panhandle, and W OK by Thursday afternoon. My hope is that, since it's looking more and more like this wave will move too fast for a good chase day on Friday, we see a continued progressive trend in the models such that mid-level temperatures cool a bit more Thursday afternoon over OK/TX. Right now, the NAM depicts 700 mb temperatures >10 C over the dryline, while the faster GFS solution is in the more breakable 5-8 C range.

Initiation of surface-based convection before sunset may be a long shot, and tornado potential is even more questionable given likely-high LCL heights, but it's always hard to ignore the monster hodographs you get on days like this if there's any chance of storms forming. Whether the moisture advertised on the models materializes after the beating the Gulf took this weekend remains to be seen, but at least there seems to be a slight upward trend on moisture quality and depth the past few runs. Given the fall and early spring we've endured so far, I'd be more than happy to chase a rogue high-based supercell with decent structure for a couple hours Thursday evening before the cap eats it alive.

 

[Skip Talbot]

Thursday screams cap bust. Both the NAM and GFS are showing a thermonuclear cap over the dryline/cold front. Cap indices erode a little at 0z on the NAM:

But even a cap index of 1 might still be too high given the main energy in the shortwave is still to the west. The GFS has the cap filling back in with a vengeance after 0z so it doesn't look like we'd get surface based initiation even after dark. The best I could see coming out of this setup are some elevated hailers after dark. Still plenty of time to change, but I'm expecting the GFS to slow down more with its progression of this trough than speed it up actually.

 

[Adam Penney]

Unfortuanately, I have prior engagements for easter weekend, and am unable to chase on Friday, so Thursday is my only option, albeit a toss-up day for sure.

The directional wind shear for Thursday certainly has my attention. If anything can manage to break the cap, we could be in business with atleast a nicely structured supercell.

As mentioned above, the 12Z GFS prog LCL's appear to be a little to high for my liking, especially over extreme WC OK at 0Z. The NAM displays better moisture return than that of the GFS, but it still looks pretty meager on this day. I do agree this does scream CAP bust, but there is still time for that to change.

This is my only day over the weekend I can chase, so I plan on chasing. However, if the CAP is still progged to be as strong as advertised by Wednesday morning, I may holf off. I am itching to chase, so I will probably just do it regardless...lol.

 

[Brandon Goforth]

I agree with Skip, this thing has blue sky bust all over it. That cap is stout. I doubt that is overcome with such marginal instability and forcing. Moisture is a problem. Sure the sfc dews around 60 don't look too terrible, but it's real shallow. The instability axis is very narrow. LCLs are high immediately ahead of the dryline and along the axis of best instability and slightly deeper moisture. Not that any of that matters anyways, because those warm temps aloft are going to keep any storms from developing out there at all... :/ Regardless, this setup should allow for some amazing sunset pics.

 

[Chris C Sanner]

Thursday is a very classic boom/bust kind of day. While the chances of a blue sky bust are really high, in the off-chance you can erode the cap and get a storm to go, it will likely be all alone and will be a decent Supercell given the shear and CAPE that should be in place. I keep trying to kid myself and say I won't be chasing Thursday, but I will likely be out near the dryline hoping something pops just because an isolated lonely supercell in Western Oklahoma would be about as good as it gets this time of year. Given the cap in place though, I might have to just get an awesome set of sunset pics

A little more in-depth forecast with pretty Twisterdata graphics on the site: http://www.supercellhunting.com

 

[Adam Penney]

Yes, I know they are off hour runs, but both the 18Z GFS and NAM are showing a more favorable CAP situaton at 0Z Friday.

18Z GFS: http://www.twisterdata.com/index.ph...nding=n&output=image&view=large&archive=false

18Z NAM: http://www.twisterdata.com/index.ph...nding=n&output=image&view=large&archive=false


While both still show a pretty stout CAP, if these runs were to verify, it now appears to be "breakable" anyway ,IMO, over SC KS/NC OK. Shear profiles on the 500/850 crossover show decent wind profiles, so again, anything that manages to break through, should be a pretty site. The NAM continues to imply much better moisture return than that of the GFS with 60 degree dewpoints extending all the way up through SC MN. While that would be great, I certainly tend to think the NAM is overdoing the dewpoints a tad.

I am looking foward to the 0Z runs tonight to see if they continue showing a better situation regarding the CAP. If the CAP can be breached, Thursday holds better supercell potential than Friday,IMO.

 

[David Goines]

Patrick Marsh had an interesting write up on his blog today about Thursday's setup. He didn't have time to post it so I'll throw it on here for him. It's really good insight about in-depth analysis of the models and things that people overlook. Instead of copying and pasting everything, here's the link.

 

[Skip Talbot]

The cap looks even stronger across the Plains than it did in previous models runs:

The southern Plains look like a definite cap bust. The window of cap erosion is extremely narrow and not complete. The 0-3km Cape slacks off right after 0z too, so if something does manage to breach the inversion in southern Kansas, it probably won't be able to hang on once the cap fills back in.

One area I've overlooked until Dean Baron brought it to my attention is the northern end of this setup and warm front play up in eastern SD and western MN. The cap looks like much less of an issue up there, and provided the moisture can indeed advect that far north, we're looking at upper 50's dewpoints in eastern SD to maybe 60 in MN. Modest instability of 1000 J/Kg could be enough for supercells. What looks most impressive is the shear, however. 50-60 knots of bulk shear and up to 300 m2/s2 1km storm relative helicity just across the warm front. The 0z NAM is firing off convection near 0z in eastern SD. The shear instability parameters should support supercells in this environment, and given the greatly backed surface winds and directional shear increase, there could be a good possibility of tornadoes as storms approach the warm front. The big question is if the moisture can advect that far north. With modest thermodynamics this setup also doesn't have much room to degrade. Eastern SD and MN is starting to look like the best option for Thursday though.

 

[Stan Rose]

I took a quick look since its a rare day off for me--but im going skiing instead! Cap is too strong, combined with narrow moisture axis its way too conditional to justify blowing gas $--ill wait for a better setup!

 

[Jason Boggs]

I pretty much agree with what others have said. Most everything looks really good to me for supercell production for Thursday, but like most already know, the fly in the ointment may very well be the cap.

Wind fields and forecast hodographs look very good up and down the dryline with great speed and directional shear. The moisture supply won't be a problem with upper 50's and maybe low 60's on the moist side of the dryline.

Models have trended somewhat towards cooler temps at 700mb, but it's just going to depend on the convergence along the dryline which may be quite strong. Also the 700mb temps are obviously very important, along with the associated lift along the dryline from various factors. I really think with the dynamics associated with the system, an isolated storm or two will succeed at breaking the cap.

I think the tornado potential may be quite good with the excellent shear and decent moisture values. Of course with the very dynamic winds in the middle and upper atmosphere, storms may be racing at 30-40 mph. Here is a little forecast graphic that I did. Take it for what it's worth, which may not be much!

EDIT: Forgot to mention that it will be very interesting to see what the 4.0 km WRF has to say about precip. production. I'm thinking the area in NW OK around the 01Z and 03Z timeframe.

 

[Jeff Snyder]

I'm not very optimistic about tornado potential, largely as a result of marginal moisture. Even if the sfc Tds are able to make it to 60F, sfc temps should warm into the 75-82F range ahead of the dryline, which will yield dewpoint depressions around 20F. A look at forecast soundings reveals that LCLs, as a consequence of the Td depressions, will be rather high for an appreciable tornado threat. The LCLs drop to a more tolerable level 50+ miles E of the dryline, but then the cap increases E of the dryline as well, so I'm sure we'd be able to sustain a storm very far E of the dryline where LCLs are lower but CINH is higher. As is relatively common for the "day before the day" setup (though "the day" may be underwhelming in this case), shear profiles look pretty good for supercells ahead of the dryline across much of the plains. However, with the primary vort max / trough aloft so far upsteam still, mid-level temps won't be particularly cold for the given low-level theta-e. This fact, combined with Tds of 57-61F, are likely to contribute only 750-1000 j/kg MLCAPE. If we had better low-level moisture (e.g. 63-66F), I'd be considerably more upbeat. Heck, the 12z NAM has higher SB- and MLCAPE in eastern NE and parts of IA than in Oklahoma and southern KS east of the dryline tomorrow. In fact, some areas in southeastern NE look as interesting to me as some areas of western OK do tomorrow.

The 12z NAM from today (just coming out now) is forecasting for the cap to weaken to a point where convective initiation may occur if sfc convergence and the dryline circulation can produce enough low-level lift. However, the instability axis is rather narrow. Overall, with LCLs that are higher than what I look for when it comes to appreciable tornado threat, and little in the way of forcing aloft, I'm not very optimistic for supercell (and particularly tornadic supercell) potential tomorrow, at least in terms of having more than one storm per state. That said, I think there is a conditional threat for a supercell if initiation occurs considering the forecast hodographs.

Note that this doesn't mean I won't chase this one... My threshold for chasing tends to be relatively low, and I love to chase beautifully-sculpted supercells (LP or otherwise), so I may still head out there even if I think the tornado prob may be very limited. I agree with others in that this upcoming shortwave trough may just "prime the pump" by helping to bring better moisture northward from the Caribbean, thereby giving us better moisture for subsequent setups. Even without entirely advecting Caribbean moisture into the area, at least this one won't wipe out the Gulf; the air over the Gulf should continue to modify and moisten (even if buoys in the NWrn GoM indicate water temps only in the 65-66F range anyway) with time as long as we're able to stop flushing it out with dry cP air... Obs do show 61-64F Tds into southeastern Texas now, though the CRP and BRO soundings show that this better moisture isn't terribly deep (only ~50 mb).

EDIT: 09z SREF guidance (see HERE) does support a good prob that Tds may reach 60F (or 61-62F) ahead of the dryline in the plains. However, I don't think a single ensemble members is forecasting precip tomorrow afternoon through evening. The instability axis will be narrow, but the lack of any QPF by any ensemble member is discouraging. Perhaps I'll take a trip W on I40 to western OK, but the prob of convection seems low at this time.

 

[Mike Smith]

Thursday evening until Friday sunrise

I think there is a good chance of scattered to broken supercells on a Taloga, OK to Minden, NE line developing toward sunset and moving slowly east during the night (cells moving NE at a pretty good clip).

There is a chance of a tornado right at the beginning, but it should develop rapidly into a hail situation.

The EHI's look good and I think the cap is breakable along the zone indicated above.

 

[Chris C Sanner]

The real fly in the ointment for chasing tomorrow isn't the cap IMHO. The cap IS a huge deal, but even more important are the forecast storm motions. I can see storms hitting 45 - 55 kts across Kansas under the stronger upper flow, which will pretty much ruin anyone's day who isn't both experienced and really on top of their game.

Otherwise, this is at least some of the best instability of the year -- not saying much -- and the setup features pretty decent shear across the target area. There might be a narrow area where you can get enough weakening of the cap to go along with slower storm motions, but that's something I have serious doubts about.

Regardless this looks like a primer system for future systems at this point, but no doubt I'll be out chasing. More detailed forecast on the website (linked in my signature).

 

[Scott Olson]

Looking at a couple areas that will have less of a concern of a cap.

NE SD/C MN : This area appears to have enough convergence to show weakening of the cap. Unfortunately the instability is rather modest here. The shear profiles are supportive enough of rotating storms and the LCL's aren't extreme but I just don't think it will intiate here.

Lincoln, NE: There appears to be a small area where the cap is weaker, I've seen this on previous runs too. Overall shear/instability setup isn't that bad for some organization but it's a big *if* as to whether the cap can be breached. It's just getting close as it is but that's assuming model forecasts of moisture.

Mission, SD: This is my *favorite*. Near the triple point appears to be enough convergence to weaken the cap and send a releatively slow moving storm pushing up along the warm front towards Winner, SD. While the instability is still a bit on the modest side, it is no less than anywhere around there and seems to peak out with EHI. The bulk shear in this region is certainly enough for supercells. Strongest PVA is also in this area with some noted cooling around 700mb. 0-1km and 0-3km helicity is strong at 200 and 450 m2/s2 respectively. Lackluster caveats may be Tdd being upwards of 18F and that assumes that NAM moisture fields aren't overdoing moisture!

 

[Brett Roberts]

Thanks to the mods for adding KS/NE, which look more promising now than when I started the thread.

At first glance, the trend on the 12z NAM for cooler 700 mb temperatures and less CINH immediately ahead of the dryline in OK/KS looked encouraging. Unfortunately, the model appears to be severely overestimating current surface dew points. The difference between the better-initialized RUC and the 12z NAM by 00z tonight over OK, TX, and the western Gulf is simply staggering. While the end of the RUC forecast period is still 21-24 hours prior to tomorrow's potential setup, it's hard to believe the impact of (likely) excessively overdone low-level moisture upstream at the beginning of the forecast cycle on the NAM will not continue to be felt tomorrow. If Td's along the dryline tomorrow afternoon verify substantially lower than the current NAM forecast of ~58-61 F, the already-conditional threat for daylight supercells will probably vanish. We'll see how the obs evolve today and tonight, I guess.

Right now, SE NE looks like the most interesting target to me, even though both moisture concerns and warm mid-level temperatures will plague that area as well.