3-28-07 FCST: SD / NE / KS / OK / TX

[Mark Farnik]

I completely agree with Gabe's well drawn comparison between this upcoming event and the March 13, 1990 outbreak. I don't think this will be an exact repeat, persay, as Gabe already said, but I have a feeling that as with that oubreak we will see two primary areas of tornadic activity: one in northern KS/southern NE near the triple point, and another in western OK along the dryline, with the former seeing more significant activity than the latter. The moisture setup and dynamics, again, aren't dead ringers for the March 13th setup, but they bear a fairly strong resemblance.
SPC mentions in their 0600 outlook that areas of the Slight Risk area will likely be upgraded to Moderate Risk in later outlooks. I'd be willing to be the entire hatched area from northern NE to northwestern OK will be upgraded to Moderate Risk once they get a better handle on the potential convective mode and the associated threats.

My preliminary target is Lexington, Nebraska, right smack in the center of the hatched area and with excellent road options. I plan on being out the door by 10 a.m. so as to reach Lexington by 2 p.m. CDT in order to gather data and further refine my target before initiation. Then it's showtime!

 

[Brian Stertz]

Hmmm....

If the 12z ETA is to be believed...this system appears to be disjointed as with the past couple systems. It looks like the most favored area for tornadic supercells will be from the eastern part of the Nebraska Panhandle/Sand Hills southeast towards the North Platte/Broken Bow/Gothenburg Nebraska areas. This particular area will have 50kts. plus of 0-3km shear and CAPEs of 1500-2500 j/kg. Similar to the system this past Sat., it looks like all of the main upper dynamics will be driven almost due north, with very limited overlap into the warm sector. If I was able to be chasing tomorrow...I would head to Ogallala/Arthur NE and hold there tomorrow around noon. That is where the big game fishing will be on this event. Not all that excited about points south of the Nebraska stateline.

 

[Donald Giuliano]

I'm pretty sure that this is simply convective feedback, since the moisture depth and magnitude should be high enough that mixing will have only a limited effect on the sfc dewpoints. We've had several days of return flow, and from the looks of recent soundings, a tropical airmass is already in place across the Plains. Rest easy...

Gabe

I'm inclined to agree with you about convective feedback, Gabe, as looking at the CAPE fields it seems pretty obvious to me that if the NAM's dewpoint forecast for 18Z verifies, then we're going to be dealing with ~3000 CAPE ahead of the dryline, even along about 00Z. Though I have to say, there's still plenty of instability available, even if dewpoints are only in the low 60s.

I've been watching this event with increasing interest, despite it looking somewhat non-classic. The hodographs look pretty darn good to me, unless I'm missing something, and I am unsure as to why people are suggesting they are too linear. The initial Bunker's storm motions (taken from Nsharp) are angled about 30 degrees off the axis of the dryline from SW OK to NW NE with a dryline-relative component of 15-25 kt (depending on location), with the right-movers at about 45 degrees and a dryline-relative component of 20-30 kt. Combine this with a dryline forecast to be slow-moving, especially farther south where storm motions are progged to be slower, and that should be sufficient to keep the convection from going linear for some time.

Right now, if I had the ability to target any location, I'd be torn between fast-moving but possibly widespread crazy-intense storms in NE vs somewhat slower-moving, but possibly not quite as widespread or intense, storms down in OK. Since I don't have that ability to even consider NE during the work week, targeting Woodward seems to be a good option for me, as it would allow me to play the southern 1/3 of KS, as well as most of OK (since the storms should be moving NE). There's still an awful lot of uncertainty, though, especially since this system is a cut-off...we all know how well the models handle those. Tomorrow morning's obs should be very revealing.

Also, I like the case from 1990...nice find, one has to go back a ways to find cut-off lows that got the job done in OK, but those cases do exist. Some of them even have southerly winds at 500mb.

--Don

 

[Reed Timmer]

Great analysis Don!

My only worry about further south was the storm motions being too parallel to the bdy...but since the dryline will be almost stationary by peak heating, it doesn't look like we'll have any problems.

We're definitely favoring western NE on this one! Mixing won't be a problem...for the northern or southern mode....given the depth of the moisture and the southeasterly 850mb flow to the north.

This is going to be INSANE!

 

[Mikey Gribble]

Over the last 24 hours I have started to get pretty excited about this system. Not that I think it is an ideal setup or a sure thing by any stretch of the imagination, but I do think this is definitely the first real shot at tornadoes in the plains this year. There are a LOT of things that could be better, but there is enough for a tornado outbreak IMO. I have started to second guess myself a little bit, but I am still far from changing my target. If you drew a line from Hays to Kearney and connected both ends to the dryline, I think that box is going to be the bullseye for tornadoes. I also think there will be a tornadic storm coming off the dryline in southern to central Kansas and maybe a few tornadoes in the Oklahoma-Texas area. I am pretty damn sure though that the place to be will be in that Kearney to Hays area.
Hodographs in Hays and Kearney are supportive of tornadoes by 00Z. 0-3km helicity should be around 300m2/s2 by 00Z. If I was going strictly off the models, I would be a little worried about LCL's being a little high in the Kearney-Hays area, but I really don't think moisture is going to be a problem after looking at current obs and considering the backing winds tomorrow.
As far as convective mode goes, I am becoming less and less worried with time about this being an issue. I am very interested to see what the WRF precipitation graphics show tonight. Like somebody mentioned earlier though, the shear vector goes away from the boundary enough for storms not to go linear right away. They are also going to move off the boundary really fast. Which brings me to storm motions. That is definitely going to be a problem. I would leave the tripod at home tomorrow and bring the radar detector instead. I am definitley going to position myself a solid 30 plus miles ahead of where I think my storm will fire.
I am pretty optimistic about our chances tomorrow. Of course every year I get "pretty optimistic" about a few setups early on that don't verify, but IMO everything we need is there for a few tornadic supercells tomorrow. I wouldn't anticipate wide spread strong tornadoes, but long track is definitely possible given storm motions and I wouldn't be surprised to see a couple strong tornadoes in that Kearney to Hays area. If I was doing the SPC forecast I would go moderate with 15% hatched on tornadoes from Hays to Kearney.

 

[Jason A.C. Brock]

Ill want to take a look at things later tonight and even again early AM tomorrow but right now I like the area near Woodward Oklahoma. The area up in NC KCS AND SC NE may indeed see more rubust and dynamic storms but I prefer to stick with the slower moing perhaps more isolated cells further South along the dryline. The storms in Nebraska (while they will be magnificent the first couple hours) will be screaming NE and also will likely have some company fightning with other cells for the atmosphere after a couple hours. One will need to keep in position on the cell that has the best unimpeaded inflow areas and watch for things that can stay ahead of the other cells or remain more isolated for as long as possible. Trying to position oneself amogs all the cells may be a chore with the screaming NE like they will. Getting in the right position on the initial cells will be critical.
While the storms futher South in Oklahoma may not have the added tornado juice they should b jsut fine. They should have plenty of moisture and daytime heating and enough of a cap to keep them more Isolated at least until dark. We may not get initiation until 4pm unlike up north where cells may fire as early as early afternoon.
Everyone should ahve their fair share at photogenic supercells picking either target and it will be good having chasers in both areas. I am a little worried about two things with the Oklahoma area..well kinda with both areas.....Some of the models want to slow down the system a tad. If this is the case (especially accross Oklahoma) We may see storms not fire until close to sunset which would be a shame. The area further North would then get later afternoon storms but still have some hours to work with before darkness.
Also the storms in Oklahoma may initially be very Isolated. So a storm may fire 100 miles away and getting to it in time could be an issue. I hate it when a cell fires 100 miles North and you are not sure if you should go on after it or wait and see if something else may fire closer or to the South. Grrrrr The 100000000000s of possibilities each system brings....I guess thats why we have supercomputers" and even they screw the pooch many times.
So as of Now Target Woodward Oklahoma but it may very well change. I would love to get storms further South in Southwest Oklahoma. It usually never fails when we have some setup with a trailing dryline and Moderate risk to the North that something tailendish and ery isolated occurs...say....Childress Texas?
Good luck to chasers in all areas and stay safe.

 

[afischer]

Well this'll be the easiest "tough" forecast I've ever made; I have to work tomorrow night, so have no choice but to play the central & northern KS portion of the dryline. How convective mode will evolve in this particular region remains to be seen, but we've certainly seen tornadoes before with a vertical "veering/backing" pattern so I am holding out some hope. The NAM & Goofus sr-hodographs look mighty fine to me the past couple model runs in north-central and central KS given a typical rightward-deviant storm, especially by 00Z... with 1km flow increasing to 40kts and remainined backed to nearly SSE.

 

[Gabe Garfield]

Analogs to the Projected Setup

Interesting comparison Gabe, and I can see some similarities but that one does not appear to be a closed low at 500mb which we will see developing, nor does it have a single cyclone aloft. In that map it appears there is a double-barrelled structure to it. Furthermore, that case does not have a weakening shortwave devolving from a slow-moving closed low ejecting northeastward into the Great Lakes. Thus, the ridge in the 1990 case is much more amplified downstream of the trough. Not to say it won't be similar, just I think there would be better matches. I checked the perfect prog analogs and it seems that there are other matches for the 500mb pattern and in fact two analog very close in 500mb and 850mb patterns which makes me think this event will probably model those events very closely. The first is May 8, 1986 and the second is April 12, 1991.

AJL

Good comparisons of past events. The 500 mb flow for the May 8th event looks quite similar to this setup, but the flow for this level looks a bit more veered in the April 12, 1991 than what we will see tomorrow. In any event, it is heartening that those days produced at least some tornadoes.

Regarding the 1990 case, the upper-low responsible for the event *did* cut off the next morning. Additionally, the shortwave trough *did* weaken the next morning and was by no means progressive. See the following links:
http://vortex.plymouth.edu/cgi-bin/gen_ua-r.cgi?yy=90&mm=03&dd=14&hh=12&re=us&ge=640x480&bg=white&com=35&sc=1.0&va=all&le=p500&pl=dp&in=30&co=26&va=no&le=p500&pl=ln&in=30&co=35
http://vortex.plymouth.edu/cgi-bin/gen_ua-r.cgi?yy=90&mm=03&dd=15&hh=00&re=us&ge=640x480&bg=white&com=35&sc=1.0&va=all&le=p500&pl=dp&in=30&co=26&va=no&le=p500&pl=ln&in=30&co=35

Also, I'm not sure what you mean by "double-barrelled" structure; I imagine you are referring to the lows drawn in by the analysis algorithm. The thing is, the rawinsonde observations do not support the existence of separate lows.

While I'm not saying that there will be a major tornado outbreak tomorrow, I believe that there is the potential for one. Just because flow is more meridional than one would like to see does not preclude the risk of a major event. Not every major tornado outbreak is forecasted well in advance.

Also, I'd like to note that very experienced forecasters at the Storm Prediction Center have a difficult time forecasting storm mode, so I believe it is wise to be open to the possibilities.

Gabe

 

[Mikey Gribble]

I agree with everything your posting Alex and if you go back and read my post you'll see that I said...

"I wouldn't anticipate wide spread strong tornadoes, but long track is definitely possible given storm motions and I wouldn't be surprised to see a couple strong tornadoes in that Kearney to Hays area."

It sounds like you are thinking along the same lines as far as storm reports will go. This isn't going to be a widespread tornado event, but it will be a wide spread sevre weather event with a fair number of tornadoes (a few possibly strong).

There are two things that are making the target decision tough for me and that is low level shear and convective mode. Convective mode is certainly an issue at the Neb-KS border target. I think that storms are going to be too clustered/linear once you get North of the border, but I think storms that fire South of the border (West of Hays vicinity) are going to be discrete enough. I would hands down take the southern target IF (that is a big if) low level shear was as good as it was up North. Both directional and speed shear are better in the low levels at the northern target. My target is based off a compromise. I am banking on a storm going up South of the Kansas border and tracking into the area of better low level shear. I honestly think both areas are going to produce a few tornadoes tomorrow, but I think the most likely place for strong tornadoes is going to be in that Hays to Kearney area. I may change my opinion after models update and the scenario becomes more clear. I have been wanting to cheat South more and more, but for now I am convinced on Hays.

 

[Adam Atkins]

Western Oklahoma is looking better with each model run. The slower the system, and further south near the base of the trough, the more veered the mid-level flow, which will help storms quickly get off the boundary. The 18z NAM KCSM (Clinton) sounding looks very good. Deep layer shear and storm motions are much better for chasing.


http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=META&fcsthr=030&STATIONID=kcsm

My concern is the completely mixed boundary layer along the dryline which could lead to too many storms. All of the models have been eroding the BL capping inversion completely leading to free convection.

Now again, this is only a model forecast but this system has been trending towards a stronger solution in each subsequent run. I expect even the naysayers will be out tomorrow. Now if I could only sabotage the tv stations here in OK....LOL, just kidding David Payne, Val Castor, etc...you're entitled to chase too, I guess.

 

[David Wolfson]

With each run the high plains possibilities are looking ever-less rosy. The upper system is holding north and well into the mountains. The whole CAPE, moisture, low-level helicity, and shear picture just doesn't look to be coming together. Tomorrow's system should be kicking a rather powerful trough line through AZ right now -- mountain showers, Cu congestus at low altitude. It's not happening, with the surface manifest already up into southern UT and extreme southwestern CO.

So my virtual target for tomorrow is San Angelo, TX. The traditional ingredients are there to a moderate degree. The 36-hr RUC is showing some low-level backing, with decent moisture, CAPE, and dryline. Throw in a little shortwave bonus, and it could actually be pretty good down there IMO. Then it's a northward amble for the 29th. FWIW.

 

[Donald Giuliano]

I could be missing something, but the hodographs for tomorrow don't look particularly linear to me. Here are a few forecast hodographs near a few towns valid 00Z 29 March:

Ainsworth, NE: http://129.15.195.166/ainsworth.png
Kearney, NE: http://129.15.195.166/kearney.png
Wichita, KS: http://129.15.195.166/wichita.png
Watonga, OK: http://129.15.195.166/watonga.png
Altus, OK: http://129.15.195.166/altus.png

 

[Donald Giuliano]

With each run the high plains possibilities are looking ever-less rosy. The upper system is holding north and well into the mountains. The whole CAPE, moisture, low-level helicity, and shear picture just doesn't look to be coming together....

This is a good point, especially since the models are not in the best of agreement, with some of them (e.g., the UKMET) getting the system hung up in the mountains (boring), instead of sliding east a little further and then stalling as per the NAM (possible outbreak). There's definitely a lot of uncertainty here, due to the nature of cut-offs. I'm very much looking forward to tonight/tomorrow morning's obs to see how this is shaping up in the real world.

--Don

 

[Mikey Gribble]

Adam, deep layer shear in the sounding you posted a link to is 49kts. The NAM has been showing 50kts all along the dryline from the NE-KS border all the way down to west central OK. There is litterally no difference in deep layer shear between the targets.
Forecasted storm motion (using Bunkers) shows less than 10kts variation between the OK and NE-KS target.

 

[Adam Atkins]

I never said there was a difference in the magnitude of deep layer shear. The shear vector backs to a more meridional vector north of the W Oklahoma target, which was my main point, and might not be favorable in terms of chasing discreet storms.