4/21/07 FCST: OK / KS / TX / NE

[Rich Thompson]

Rich -

That's a pretty good match! How exactly do you go about finding analagous events - do you guys have a good database or is it just a keen memory? I'd just say the only obvious difference at first glance is that the surface low in the 4/6/01 case was much deeper, by ~10 mb.

Otherwise -

The dryline keeps getting pushed further west. If you're going to chase this on Saturday and had originally planned on going to the TX Panhandle you may need to head close to the NM border. I'm still debating on whether or not to head out and a lot depends on whether or not I can ride along with someone.

Still, plenty of shear spilling past the dryline. Despite moderate instability the strong shear favors supercells. Still difficult to tell how quickly it will go linear. The 12z NAM does have a little pocket of 150-200 m2/s2 0-1km SRH in the C TX Panhandle in the mid-late afternoon. Winds are out of the southeast so good veering on wind profiles. I wouldn't rule out a few tornadoes. I think that the volume of hail and to a lesser extent wind reports will probably dictate a mod risk somewhere unless a lot changes between now and Saturday. Don't give up the hope on isolated tornadoes yet though! Shouldn't be a tornado outbreak but a decent severe weather outbreak.

AJL

Alex,

That loose analog was from memory (I worked the event back in 2001). I'm not saying the outcome will be the same, but it does offer some insight into the possibilities with the upcoming system.

Interestingly, that was one of the first "dry hole" forecasts I can recall *before* anything was apparent in observations across the conus.

The notion of a squall line Saturday comes from the solid band of precip on the dryline. Of course, the model resolution is so course (compared to the storms) that it could mean any number of things from lots of supercells to a line, to anything in between. We (SPC) have some post-processed output from the NAM that shows the potential for mixed convective modes (both line segments and discrete cells) along the boundary Saturday evening. The 4 km WRF runs will be amusing to see by late Friday night.

Rich T.

 

[cdcollura]

Good day,

We also have to bear in mind something that tends to happen if low-level backed winds, developing low-pressure, moisture convergence AND a negatively tilted trough being not "quite" in the right places above and below each other.

I have this explained in GREAT DETAIL in the interesting post in WEATHER AND CHASING below ... Please feel free to look at it.

http://www.stormtrack.org/forum/showthread.php?p=132377

The point about this is that if there is too much of a negative tilting of the trough as it is moving east of the Rockies, the developing surface low will have to be right beneath a small area where a difluent WSW wind is aloft, assuming surface winds back to SE. If they are both SE aloft AND at the surface, that's about the same as SW at all heights (unidirectional, speed-only shear).

If this pattern happens, then a squall line will be likely.

 

[Craig Maire II]

I'll be taking off tomorrow morning or early tomorrow afternoon and heading towards western Kansas (somewhere between Dodge City and Goodland). I believe that sitting along the Kansas/Colorado border will serve me best and am definitely confident that supercells and a few tornados will develop Saturday afternoon. By camping out in western Kansas tomorrow night I won't have to rush to the target area as I had to do on 03/28/07 (won't be tired and insane LOL ). Both the Goodland and Dodge City NWS offices are talking about tornados in they're hazardous weather outlooks and SPC has a 30% outlook for that area. I do believe that a moderate risk will be issued either tomorrow or on Saturday and that Kansas will bring me some beautiful storms and maybe even a tornado or 2. There are far to many atmospheric variables and this system is still a few days out for anyone to say if this will or won't produce a decent number of tornados, supercells etc., one thing I have learned from my 9 years as a storm chaser is that nature is FULL of surprises!

 

[Joey Ketcham]

To chase or not to chase..

My main worry is the storms forming into a squall line, it's not too bad with embedded supercells.. but depends on how fast they're expecting the storms to move. Don't want to spend all day playing catch up.

 

[Stan Rose]

Sig tor parameter (which incidentally was an excellent predictor on Mar 28) based off the 12z nam puts a bullseye in wrn TX panhandle, coincident with the highest helicities, and where the model seems to like discrete cells coming off the NM terrain. Id rather not drive that far, and there are plenty of other factors to consider, so w'ell see (by 21z sat)

 

[Brian Stertz]

Yeah I was seeing that too Matt...the higher tornado/sig severe parameters from 12z ETA are focused between Lubbock and Clovis. Looks like the higher lapse rates are favored across EC/SE New Mexico into the SW Texas Panhandle and NW TX South Plains area. Very strong 0-6km shear and probably just enough instability to make things fun before dark and the squall line scenario plays out.

 

[Jeff Snyder]

AMA recorded 700mb wind speed of 140kts at 00Z 010407?? Is that to be believed? I assume that's RAOB data? I will say I was trying to keep ahead of the line on US60 at about Panhandle TX, exceeding the 70mph limit, and the line was STILL overtaking me. Of course, that's not news to anyone who chased that day.

No, that isn't to be believed. The 700mb level is the last mandatory level at which winds were reported, and, the unrealistic speed, I'd disregard that wind observation as well.

Another distinction from 4-6-01 is the strength of mid- and upper-level flow -- At 500mb: 60-85kts on 4-6-01 across the warm sector ahead of the dryline, as opposed to 40-55kts forecast Saturday evening. Well, perhaps it's not so much that the 500mb flow is that much weaker than the analog, but it's that the jet streak ejects later in the day than was seen earlier. The 12z NAM storm motions are <40kts from storms east of the NM/TX border, so I wouldn't be too cocnerned about storm motions with this system. Of course, as the jet streak lifts out of the base of the upper-level trough/low, storm speeds should increase with time.

Not that Rich brought up the 4-6-01 case to be an identical setup... It is an analog, but I wanted to point out one difference that should result in more chaser-friendly storm motion.

IMO, the upper-level trough passage is about 12 hours too late. If we could take the 12z forecast, and force it to verify at 00z (12hr later or 12hrs earlier), I think we'd be much better in terms of significant supercells in the Plains. As it is now, I expect a potential MDT risk, mainly for the risk of hail and wind damage. One mitigating factor for wind damage is that the strongest mid-level flow doesn't really work into the warm sector until 6z and thereafter, when the low-levels should be considerably more stable given nocturnal cooling. With more stable air near the surface, it's more difficult for damage winds to make it to the surface.

With the fact that it looks like initiation will occur in eastern NM through far southeasern CO, I'm more likely than not going to sit this one out. The next system coming through looks as though it'll have much better moisture to work with, so I'm not down-and-out yet. Of course, this all depends upon the NAM verifying, which is certainly not something in which I'm putting a whole lot of confidence.

EDIT: Stupid me -- I forgot to make a very important "NOTE": The 12z GFS solution is faster than the 12z NAM solution, with the dryline located in the central OK panhandle and not too far west of AMA by 0z. In addition (and not unrelated), the upper-level trough is a little farther east on the GFS compared to the NAM by 0z (though there's some convective feedback/modification in the fields in northern TX panhandle by 0z).

 

[Gabe Garfield]

Another distinction from 4-7-01 is the strength of mid- and upper-level flow -- At 500mb: 60-85kts on 4-7-01 across the warm sector ahead of the dryline, as opposed to 40-55kts forecast Saturday evening. Well, perhaps it's not so much that the 500mb flow is that much weaker than the analog, but it's that the jet streak ejects later in the day than was seen earlier.

By the way, the date of the "analog" case was actually 4/6/01. In any event, that case was a bust (as far as significant tornadic supercells are concerned), and this system has less going for it than that one did. IIRC, Tds were in the mid-60s w/ the 4/6 case (not to mention that this system will be significantly farther west).

IMO, I think this system may eek out a tornado or two before going "squally-squall" pretty early in its evolution. Even if storms remain discrete for longer, the moisture just isn't looking terribly impressive. Top this off with the "slower system" trend in the models, and you've got an abysmal severe weather setup for chasing (for all chasers not Panhandle-based).

Gabe

 

[Michael P. Morris]

Most of my concerns have already been echoed by other posters, namely the trend of the WRF to build a slower, albeit stronger upper level system. On the other hand, the GFS predicts a weaker but faster solution, while the EC produces a decent compromise. Regrettably, however, the GFS no longer places a surface low in the SW Kansas region and has significantly weakened its forecasted instability to less than 1000 J/kg over most of the eastern Panhandles and SW Kansas.

Hopefully the next two runs will start to converge with respect to the intensity and positioning of the upper level disturbance as well as the available moisture and instability. Regardless, I no longer think Woodward would be a good starting point, perhaps Shamrock would be better as it offers easy travel along major roads in all directions as well as the good folks at the Best Western. For what it's worth, the GFS produces a significant vertical velocity anomaly crossing through the central Oklahoma panhandle at 0Z (and yes, I am aware of the folly of using a coarse-grid vertical velocity forecast to infer the presence of a storm ) as well as a decent amount of shear. If that verifies, there may be a photogenic supercell out there for the taking.

I have backed off a little on my enthusiasm, and since we were flying back from Las Vegas during the 3-28 event (it was quite beautiful from the air, I might add) I have to make sure that I am not chasing out of desperation or to "make up" for missing that one. Needless to say, we will know a lot more in 24 hours or so.

 

[Billy Griffin]

Just landed back in OKC. Honestly, I'm hoping the TDs stay ~ 60 vs. upper 60s. That's all you need for high plains magic and what's more, these could remain LP cells for quite some time. I think there's enough upper-level energy associated with this system to give us some nice storms and at least a shot at a few tornadoes. And again I say, at least it's over the more preferred chase terrain and not in the jungles. I'm still not too worried, other than I was hoping the action would be a little closer to the OK / TX panhandle border. Still sticking to my original target for now... McLean, TX.

 

[Jason A.C. Brock]

I think everyone should go sit along the Colorado Kansas state line. Yup Norman guys....head up there.....look into my eyes ...............you want to go to Kansas....far away from The Texas Panhandle.....you hate Texas.....stay awwwwaaaayyyyy. ;-)
Seriously tho......The original idea of storms in the East Texas panhandle I think is a bit flawed....Id much rather be in at least AMA watch for storms forming even West of there. Alot of the sytems that have occured this year have started off further west that advertised. March 28th SE Texas panhandle and storms formed in Central Panhandle....April 13th DFW area and storms fire in Western North Texas.
The day of the New Mexico tornadoes storms were supposed to form more towards West Texas.
Just something to keep in mind. I am jsut hoping this isnt a mostly nocturnal event and that storms dont fire in Eastern New Mexico. Id rather have them form in the Eastern Panhandles as many probably do but its the weekend so im prepared to go to New Mexico....or my backyard....whichever gets me close to a storm.

 

[Matt Hines]

Most models take the dryline back to the Texas/New Mexico border on Saturday. With the 500mb low holding back into New Mexico until 0z Sun, I am going to buy into this now. There is some unidirectional sheer showing up on some of the latest runs of the GFS, but I still think the first 3-4 hours could be fun to chase before we begin to squall out. LCL's and Helicity from AMA to CVS are looking pretty good as of now as well. Of course, I will have to be in-house on this one since it may effect AMA.

 

[Jim Tang]

The ECM pretty much agrees with the NAM on the slower timing. GFS has nothing against those, so I'd say throw the GFS out. I think this could be a good LP sup event in eastern NM & CO. I'm pretty concerned about too much forcing, but with some cap and with possibly delayed impulse, there could be a few discrete sups. Best area would be where directional shear is enhanced, and that's over NM/TX, and plus the cap is a bit stronger there which could prevent a linear mess. In addition winds will be backed with a broad sfc low. Where they are more backed, low level shear will be enhanced and so will lift thru orographics and/or greater convergence.

 

[Jim Bishop]

Despite good low level curvature in forecast hodographs in the Texas Panhandle and strong deep layer shear, I'm concerned about rapid linear development, or a quick transition into a squall line.

The problem I see is the lack of a more southwesterly or even westerly wind component in the mid levels. 500mb flow is forecast by the WRF to be 55-65 knots out of the south-southwest, and 700mb flow is forecast to be straight out of the south around 50 knots. With backed 850mb flow, storm motion will be north-northeast. And given the 1000 j/kg CAPE, as apposed to 2000+ CAPE, I would assume the 700mb flow will be the primary storm motion driver rather than the 500mb flow. This means storms will ride nearly parallel to the dryline, and thus likely become some type of linear mess rather quickly.

If somehow storms can move more to the east away from the dryline, then I'd say tornado potential is pretty good based on forecast hodographs in the Texas Panhandle. Moisture won't be incredible with mid 50s dewpoints, but on the caprock that's all you really need. Otherwise I think we're looking at a tornado or two early on in a storm's life, and then a rapid transition into a big squall line.

 

[Jeff Snyder]

I wish to point out the 00z GFS run, which looks awesome (at least in a kinematic sense) for the TX panhandle. It's faster than the NAM,and it has nearly meridional 500mb flow north of I40 (or at least from the OK panhandle northward). However, the wind profiles near and just south of I40 are very impressive: SSE 850mb flow at 40kts, S-SSW 700mb flow at 55kts, SW 500mb at 60kts, WSW 250mb at 80-90kts. That, as we say, is the money shot. In addition, the 00z GFS seems to indicate that storms will be in the central and eastern panhandles by 0z. Check out the difluence at 250mb valid 00z over the OK/TX panhandles and western OK/KS! 8)

Of course, moisture concerns remain, but it seems that the NAM's latest run shows slightly better (in magnitude and areal extent) instability / CAPE. I haven't seen any CAPE forecasts from the new 00z GFS run, though.

This event is right on the borderline for me. On one hand, it's Saturday, and I think there's a good probability of significant supercells. On the other hand, it's tough for me to get excited about a drive from OUN to AMA, LBB, DLH, etc in late April with the potential for a rapid transition to squall line (which seems like a good bet if the NAM verifies). In addition, it seems that Mon-Tues may offer a better opportunity for tornadic supercells. Then again, the forecast for Mon-Tues could turn to garbage, and the Sat event could light up, and I'd kick myself if I don't chase Sat because I intend on chasing Mon-Tues (that bit me on 6-9-05). All of this is leading me to flip-flop (optimistic, pessimistic, optimistic, etc). Oh well, that's part of the fun of chasing hype, I suppose.