5/10/10 FCST: TX / OK / KS / CO/ MO

[Mikey Gribble]

Personally I still think a compromise with the surface boundary locations between the NAM and GFS is the best way to go. The area between the two dryline locations continues to shrink though, so the picture is starting to become a little more clear. Both solutions show this in good chase country so its not a big deal. I'd certainly prefer a slower solution with strongly backed low level winds, but if they do veer slightly I don't think it will matter much.
All indications continue to point towards this being a major tornado outbreak. The 12Z NAM took it down a small notch IMO, but it is still definitely an environment capable of strong/violent long track tornadoes. Before it was insanely good, the 12Z NAM is like half way insanely good lol.
There were several changes with each model this morning that would impact the tornado potential, but I just got done typing out a monsterous forecast post on my blog so I'm not going over all that again. It is literally longer than the Decleration of Independence. I have got to get my forecast posts under control.
Basically this still looks like an extraordinarily potent tornado setup. The GFS dropped CAPE along the northern portion of the dryline, which appears to be a result of low level cloud cover not clearing until later in the day (saturated 850 RH), but instability is still strong. It is back in the 3000J/kg farther down the dryline and the models have been very consistent in showing that.

The biggest concern I have right now are the cap and veering low level winds. The models have only intermitently hinted at veering winds so I don't know how much of a concern that is, but it still bothers me. I have no idea of what to expect on the capping issue so I won't pretend to have an answer for that.
Even if you take the worst paramters from each model and throw them all together, this is still an extremely favorable environment for cyclic tornadic supercells capable of strong and potentially violent tornadoes. It is a higher end high risk day IMO. I wish storm motions would slow down a bit, but other than that this is about as good of a setup as you can realitically expect.

here is the link to my blog. I posted a full forecast and map there if you're interested http://loadedgunchasing.com/blog1/

 

[Russ Conlon]

18Z NAM has just come out and is just screaming Enid, OK at 00Z. Everything still looks very impressive. Will probably see (I hope) the models come upon a consensus in the next 24 hours to make targeting somewhat easier. Thanks Jason

 

[Andrew Ryan]

FWIW, the 18z NAM has amplified the 700mb shortwave and sharpen the dryline. But at the same time, the dryline bulge is gone and the 850s are weakened just a bit. This has reduced the curvature of the hodographs a bit in OK but south central KS still looks great.

Curious to see what the 18z GFS does. If it continues its trend with the 12z run, the model spread is just going to be maddening!

 

[James Aydelott]

My big concern will be the extent of the stabilized air from Sunday/Monday overnight precipitation. The southward/southwestward edge of that more stable air will be prime chasing position.

This will likely lay down a very chaseable e/w baroclinic boundary that will intersect the dry line with a pseudo-triple point.

If I had to guess now (and that's what it is, until we see the extent of the isentropic precipitation shield and its associated stabilized air) I'd say the zone of highest tornado risk would be roughly from Fairview, OK to Pratt/Kingman, KS.

Take this with a big, big horse-lick sized grain of salt.

 

[Scott Weberpal]

Gambling on chasing a lone discreet supercell may be a mistake on Monday. Monday may very well be a day that you get in position and let the supercell go by and hope it produces near your location. If one doesn't produce, try to get the next one in line. Staying up with 1 lone supercell moving at 45 0r 50 mph will be downright difficult.

Forecast storm motion off the dryline is only 25-35kts - of course that is based off the NAM forecast storm motion which does seem a little low. Regardless, a right moving storm shouldn't be moving much more than 25-30kts.

I doubt the cap is going to yield more than 1 or 2 supercells, even if it does, it shouldn't be a chore to keep up with them.

http://www.twisterdata.com/data/mod.../08/12/NAM_221_2010050812_F60_SSPD_6000_M.png

My biggest hope at this point is to get a nice storm to turn right immediately off the triple point and ride an outflow enhance baroclinic bounday. Oh what a sweet day that would be.

 

[Jason Persoff]

It is a drool fest this far out, but too soon in the season for me since I won't be out until late May...

That said: I think my target would be somewhere between Lawton, OK, and just south of DDC. What an amazing setup hashed multiple times here already.

What's key to note are the exceptionally long, curving hodograph forecasts. Here is a time-sensitive link to the NAM 60hr (valid 00z Tues) for Lawton, OK.

http://www.twisterdata.com/data/tmp...218_2010050818_F54_34.5000N_98.5000W_HODO.png

It's dizzying just to see the perfection in the lower levels.

 

[Jeff House]

Two scenarios could unfold on Monday; both would promote a good chase day. I will not discuss the outbreak scenario, as it has been well covered in previous posts. There seems to be some concerns about both morning rain and an afternoon cap; however, even a worst case on both leaves a good window that I’ll get to below. The only possible issue I see is at 850. Outside chance a morning shortwave veers everything off, but only time will tell.

The second scenario is a more concentrated area of focus bounded by morning rain outflow boundaries and the more robust cap. Morning rain is generally a good thing as long as it ejects away by peak heating. It appears it will do so; therefore, proving beneficial by leaving behind outflow boundaries. Chase targets may change, but the OFBs should be an advantage. The cap will be breached. It may not go until late, esp if a morning shortwave creates midday subsidence. However heating will be adequate near the triple point or just south of it along the DL. This second scenario is a logistically easier one to chase compared to outbreak, but might mean lots of traffic and chaser convergence. Good luck and safe chasing.

 

[Matt Gingery]

Liking the high CAPE environment. Planning on heading out of SGF after my morning final and catchin up with the tour. Classic set up!! All the parameters seem to support a worthy event. The best forecast instability of the season. SIG TOR is off the hook in S. Central Ks. on into Oklahoma.

 

[Mike Smith]

Contrary to popular belief, based on an extensive but unpublished study I did about ten years ago, most major tornadoes are preceeded by rain earlier in the day. Note: This is not true in every case.

There are several possible reasons why: Leftover boundaries, rapid destabilization, and lowered LCL's are all reasons why morning rain can be 'beneficial' in a setup for violent tornadoes.

If you wonder whether this applies to the geographic area threatened on Monday, Udall, Hesston, Andover, Ruskin Heights, Topeka (1966), Emporia (1974), and central and northeast Oklahoma (1974) were all proceeded by significant rain in the morning over the same general area. And, yes, this was true for the KC area on May 4, 2003.

In fact, the morning of the Andover tornado, there were severe thunderstorm and tornado warnings around sunrise in northern Oklahoma and southern Kansas -- the same areas that had F4 and F5 tornadoes less than 12 hours later.

With regard to Monday's setup: SPC is calling for thunderstorms in progress toward 12Z near the LLJ. I expect they will be enhanced in the vicinity of the warm front. If the new NAM is anywhere near correct, the warm front will lift north over through Kansas with strong destabilization occurring after 17-18Z.

I don't see much of a problem with morning rain on Monday.

 

[Jeff Duda]

I've been looking at the SREF since the system is now well within its range. It has been going with a faster solution much like the GFS from yesterday (and to some extent, today). In fact, the 21Z SREF from today has the surface low near or just southeast of Salina at 00Z. It suggests a SE KS target would be the place to be.

 

[Alex Lamers]

Contrary to popular belief, based on an extensive but unpublished study I did about ten years ago, most major tornadoes are preceeded by rain earlier in the day. Note: This is not true in every case.

Interesting stuff. I noticed this occurred pretty frequently in Wisconsin (just a personal observation), and often times the rain and clouds wouldn't break up over the eventual outbreak area until 17Z, 18Z, sometimes as late as 19Z. I always wanted to try to put some numbers to it.

With respect to THIS particular event, it seems to be the quintessential "boom or bust" type case along the dryline in Oklahoma and immediately adjacent parts of KS/TX. I don't know if it's been mentioned yet, but May 8, 2003 shows up on both the 850mb and 500mb MREF analogs from last evening. If an isolated supercell can get going in the 5-7pm timeframe in northern or central Oklahoma, it could become quite prolific. Hodographs really enlarge in that timeframe. 0-500m shear really increases (over 20 knots per the NAM).

Lots of values fit in the favorable parameter space for long-lived supercells (following Bunkers' research) and strong tornadoes. Using the 00Z KEND forecast sounding from the NAM: 0-8km shear 82 kt, 0-1km SRH 338 m^2/s^2, STP 11.5, LCL 870m, 0-1km VGP 0.71 (WOW!), 0-1km EHI 7.3. The list goes on and on.

The 1km SR winds are from the ESE at 46 knots (WOW! again)

I'm also a big fan of ML Lapse Rates, and in this case the 700:500mb rates are up at 7.9 C/km. Very impressive.

Of course, this is just me geeking out at the new NAM solution. The GFS is still far less impressive and more capped. We shall see how things work out over the next 48 hours, but if a solution closer to the NAM verifies, we could see some rather intense supercells in OK/KS. In all likelihood, it could be about mid-afternoon Monday before we know how strong the cap is, and how quickly it will erode (if it will).

My 2 cents...

AJL

 

[James Aydelott]

Contrary to popular belief, based on an extensive but unpublished study I did about ten years ago, most major tornadoes are preceeded by rain earlier in the day. Note: This is not true in every case.

If you wonder whether this applies to the geographic area threatened on Monday, Udall, Hesston, Andover, Ruskin Heights, Topeka (1966), Emporia (1974), and central and northeast Oklahoma (1974) were all proceeded by significant rain in the morning over the same general area. And, yes, this was true for the KC area on May 4, 2003.


I don't see much of a problem with morning rain on Monday.

Exactly spot on. Allison/Kellerville/Pampa in June of 1995 was a morning convection in northern OK day.

E/W baroclinic boundaries are left by outflow, and they can be prolific local convergence enhancers.

 

[Mike Smith]

Interesting stuff. I noticed this occurred pretty frequently in Wisconsin (just a personal observation), and often times the rain and clouds wouldn't break up over the eventual outbreak area until 17Z, 18Z, sometimes as late as 19Z. I always wanted to try to put some numbers to it.

I don't know if it's been mentioned yet, but May 8, 2003 shows up on both the 850mb and 500mb MREF analogs from last evening. If an isolated supercell can get going in the 5-7pm timeframe in northern or central Oklahoma, it could become quite prolific. Hodographs really enlarge in that timeframe. 0-500m shear really increases (over 20 knots per the NAM).

#1. There was extensive morning rain in centrral and eastern Kansas on May 8, 2003. The SFC low was just west of GBD with a warm front straight east to Missouri at 7am (I still have the sfc chart).

#2. There was a long-track tornado from just west of Lyndon to Lawrence that day.

 

[Russ Conlon]

00Z NAM is starting to trend toward GFS solution with dryline's tip of the spear bulge around Highway 81 due west of Piedmont at 00Z. So much for worries about forcing and convergence further south if this verifies. Looks like the models might be getting a consensus finally. Chickasha --Oklahoma City -- NE to Stillwater looks incredible.

 

[Jason Haller]

New Day 2 out, Mod risk of course. Pushing if further east. Reading the Area forecast discussions seems they like the GFS more than the NAM but even the NAM is coming into agreement with the GFS. I am more of a regional chaser and stick to Northeast Kansas so I may be out but if the crapvection can clear out quicker than predicted right now and allow the warm front to move further north I may have a play. Still thinking about make a run south if things are right but I can't go too far Monday. Good luck to the rest of you.