2013-04-17 FCST: TX / OK / KS / NE / MO / IL

[Darren Wilson]

I find it fascinating that the models disagree so much with each other this close to the event and also the delayed retreating of the frontal boundary. Usually the low level jet has a big say in moving moisture north in the overnight hours but that looks unlikely at this time. That tells me the low level warm air advection is going be very strong which could develop widespread connection in the frontal zone. This will in turn limit the northwestward movement of the front. I still like SW OK if the dry line can mix that far east and set up a triple point.

 

[jeremy wilson]

This chase is driving me nuts! The front seems to be stalled right now but the RAP wants to pick up northerly motion big time in the morning. Regardless, there's gonna be some monsters on the southern plains tomorrow. I've seen this setup a few times in my 14 years of chasing and rarely does it NOT produce some strong tornadoes. Be safe and smart out there tomorrow. The normanites will be out in full force along with all the local yahoos. Be respectful and wise as it'll be a dangerous day regardless of the models.

 

[Jacob Ferden]

I would describe my feelings toward this day as cautiously pessimistic. There certainly are impressive parameters in place, which may lead to a significant tornado event IF the warm front progresses far enough north and IF the front does not begin to move southward during the early evening and IF early day convection doesn't foul up the instability.

Beyond those issues, what I absolutely hate about this day is how much certain aspects of it remind me of April 26, 2009. Veer-back-veer wind profiles are showing up throughout the warm sector, leading me to anticipate a situation with questionable storm modes and precipitation all over the place. Of course, there were tornadoes on 04/26 near the triple point, but virtually everyone considers that day to be an underperformer.

So where does that leave me? Unsure and unusually confused. Normally, I would have a target in mind by now for an event like this, but until the progression of the front becomes more obvious, this is next to impossible. I almost certainly will be chasing tomorrow, somewhere. But as of right now, that could be anywhere from NW Texas to SW Kansas. My inclination is to head for the triple point, wherever that winds up being by mid-afternoon. Tough forecast...

 

[Jeff Duda]

One last post before I go to bed.

Been focusing mainly on the evolution of the RAP and high resolution forecasts over the past 6 hours or so. The RAP has been very consistent showing winds beginning to veer across S OK around this time (0500) with a northward return of both surface dewpoints and temps starting around 08-09Z. Current look at the OK mesonet winds, and a meteogram for the Norman station, shows that indeed the winds have just begun to veer slightly from NNE to NE or even ENE. However, one thing that bothers me is the absence of pressure falls in the CO/NM area, which were present earlier today. This may slow the veering and delay the retreat of the front.

The RAP has also been consistently showing precip developing across much of OK into NW TX starting generally after 15Z tomorrow, much as the other coarser models had progged. I'm not totally sure I buy into this solution for the following reasons. I suspect the forcing for initiation of this precip/convection is associated with forced lift along sloped isentropic surfaces, because certainly if the front hasn't retreated far north, there shouldn't be surface based convection north of the front (although a lot of the progged precip is indeed south of the front, but also notably east of the dryline). If isentropic lift is a suspected cause of early morning/afternoon precip, then I doubt it will verify given current mesoanalyses. Based on the 00Z OUN and LMN soundings, parcels in C/N OK will have to rise above 850 mb in order to become positively buoyant. Current mesoanalyses show that the strongest 850 mb temperature advection (a proxy for isentropic lift in that layer) is concentrated to the north across the KS-OK border and into the OK PH. While there is also lift occurring around 925 mb across much of the body of OK, parcels there may saturate but shouldn't convect. This may cause stratus clouds to develop, but current IR satellite shows a general paucity of clouds over OK. A personal observation from a few minutes ago confirms that there are only a few scattered cumulus clouds currently over Norman. Therefore, it may not be unreasonable to discount the forecasts for early day convection. It may still be possible that an early ejection of a piece of energy may be sufficient to fire off storms in the S-N oriented band across C/W TX/SW OK as progged by the RAP. We'll have to see how that evolves.

In my mind, if I wake up in the morning to anything but OVC or BKN, I say "game on" across W/SW OK and NW TX pending the late morning/midday rain chances. Otherwise, if it is overcast or mostly cloudy with N/E winds prevailing and still cool and dry, then it will probably be the NAM that ends up being right (therefore, not that exciting of a day).

 

[Greg Blumberg]

Jeff, I agree with your diagnosis of discounting the existence of overnight convection. I'll also add in the 00 UTC FWD sounding to your diagnosis. Parcels would have to be lifted through a distance of at least 1 km in order to realize any CAPE, and I personally cannot see that happening. Multiple Southern Plains SODARs and VAD wind profiles are indicating the intensification of the low level jet stream, but even so with the help of mechanical mixing, you're looking at needing to lift parcels a large distance. Most of the satellite I've seen isn't showing any convection, with the exception of NW OK/SE KS where it looks like a weak shortwave trough has set a few weak deep convective cells off.

 

[Tim Supinie]

I'm still not sure where we're going to get significant surface cyclogenesis. Without surface cyclogenesis, the surface boundary doesn't move, and all the surface buoyancy is shunted north TX. The near-surface lapse rates on the 00Z DEN sounding are pretty horrible, so it would be difficult to get a surface cyclone up there. The 00Z AMA sounding is better in terms of near-surface lapse rates, but it seems like the forcing for large-scale ascent isn't going to get there until too late. Relatedly, the three-hour pressure change map looks disgusting.

I hope there's something I'm not seeing because I'm getting pretty pessimistic about this setup being anything to write home about. We'll see in the morning.

 

[David Conaway]

I would focus around the Wichita Falls, TX. area. There are still uncertainties regarding the evolution of the surface features and what the convective mode will be as one goes further North into Western and Central OK. If the surface features become better resolved further north, then one would still be within a reasonable distance to move up into that area.

Since the models are still having their differences, I would play it safe along the dry line. The convection will be more scattered and the instability will be good. The storms will be able to mature and ingest the better instability as a result of not interacting with many competing storms/worked over atmosphere. These type of setups can go either way and is still a toss up.

In my experience with the way this system is organizing, at least a couple of monsters will develop along the dryline and maybe further South than my target area. One could follow these storms into SW.OK as long as the surface instability does take hold into that region.

I will be stuck at work and confined to just watching the show from the sidelines. I hope that everyone who does chase tomorrow is able to stay safe and maybe everything will come together for a great day.

David Conaway

 

[JamesCaruso]

Good morning all,

Looking at things quickly from here in Pennsylvania... the 12hr 00Z NAM appears to verify with the observed 12Z frontal position much closer than does the 00Z GFS, which is already too far north with the boundary at 12Z. SPC (6Z outlook) also calls the GFS the "less-likely" solution. So I am inclined to go with the NAM.

Still, with so much uncertainty as to the position of the front, the possibility that its eventual southward movement this evening will undercut storms, not to mention that in any case the mid-level flow will be parallel to the frontal boundary, I would play the dryline a little further south into northwest TX, initially/preliminarily around Knox City / Munday and adjust from there, possibly migrating north/northwest toward the triple point as its location becomes better defined. Usually I like to play the triple point / warm front but with the frontal boundary orientation and other concerns I feel south on the dryline is the more conservative play, although my concerns there are that the convergence along the dryline does not look all that great. But the NAM does show maximum CAPE in northwest TX.

Just take this FWIW, I have nothing at stake today and just looking at this quickly (should be working now! as a "warmup" for next month's chase vacation. Look forward to everyone's thoughts. Good luck and be safe.

Jim Caruso


Sent from my iPad using Tapatalk HD

 

[Jacob Ferden]

The progression of the front coupled with the northerly surface winds in N OK have cleared up the picture a bit...what seems likely to take shape to my eyes is a NNE-SSW oriented frontal boundary, roughly along an Altus-El Reno-Stillwater line...dewpoints are quickly rising into the high 60s in central Oklahoma as the warm front arrives. Storm mode remains a question. The latest HRRR shows a cluster of storms developing and moving into the OKC metro, with indications of both linear and supercellular elements. Given the proximity to home, I likely will not be straying very far. But I do see a scenario where a tornado outbreak of decent proportions may happen if storms can stay at least semi-discrete. Yet I also see a scenario where storm mode precludes tornadic activity altogether. We'll know in a few hours.

 

[Russ Conlon]

Got a bit of a stubborn cloud deck right now. Hope it burns off here soon and latest satellite imagery is showing hints that may be beginning. Warm front progression has been very aggressive this morning. Medicine Park, Fort Cobb, Apache, or Elgin look like decent targets for positioning with triple point looking to set up somewhere between Altus to Elk City. Stay safe out there today everyone!

 

[James Gustina]

The RAP caught that morning frontal surge pretty well. If the western edge of it lifts past Hobart I will be satisfied. 0-1km shear looks absolutely insane (45kts+) and with any luck initiation will hold off until mid-afternoon for peak heating. It'll be interesting to see the 16Z sounding OUN sends up now that the front is finally past.

 

[Mike Johnston]

The RAP caught that morning frontal surge pretty well. If the western edge of it lifts past Hobart I will be satisfied. 0-1km shear looks absolutely insane (45kts+) and with any luck initiation will hold off until mid-afternoon for peak heating. It'll be interesting to see the 16Z sounding OUN sends up now that the front is finally past.

Well, consider yourself satisfied, then. Oklahoma mesonet shows Hobart conditions in the last few minutes went from 57t/56td to 70t/70td. Winds changed from northeasterly to southeasterly at 21mph gusting to 30.

At any rate, I think maybe that little section of southeast KS may be a secondary target today. Instability has really been building into that area, and what storms have popped up have showed tops > 40K feet. The mesoanalysis is showing very high 0-1km helicity over the whole moderate risk area. Overalll, looks like a great ingredients-based tornado forecast. Good luck to all chasing.

 

[Elinor McLennon]

My first post in target area. I apologize if it's not done up to standards. At 11:45am we literally drove into the warm front in OKC. It was at 235/Broadway and Britton Rd. We had an 8 degree jump in temp in the blink of an eye. Windshield totally coated in moisture. Couldn't see anything for a few seconds. Saw a pile up at Lake Hefner and 63rd in OKC. Again temp was around 77 and I'm assuming they had that same instant blinding/fog effect. Will be interesting to see where the warm front finally stalls. I am 20 miles North of OKC and we are sitting at a balmy 61 degrees.

 

[Damon Lewis]

Virtually all of the moderate risk area in OK is now under Tornado Watch 116 until 11:00pm.

 

[Derek Weston]

Virtually all of the moderate risk area in OK is now under Tornado Watch 116 until 11:00pm.

Not a particularly impressive watch from the spc. 30/50

Better params are up in Missouri currently. The best thing that could happen for the southern target is for things to hold off for a while... should it go haflway early it may be rather mundane. Need more turning with height than is seen now.