2015-05-26 EVENT: TX, OK

[Ben Holcomb]

Thought I'd start a thread since the 00Z NAM is looking pretty decent for tomorrow. Large amounts of CAPE sitting over Southern Oklahoma and North Central Texas. Sicle shaped hodographs around 00Z from Lawton to Stephenville, TX as an upper level disturbance ejects across the area. MLCAPE values of over 4000 could lead to some intense storms.

Here's a couple of forecast soundings

 

[chrisbray]

I'm eyeing IL for a sleeper play. Both NAMs seem to be keen on upwards of 2k cape working up towards chicagoland and decent shear, but I will wait for the RAP to chime in and how overnight convection plays out and check back in during the morning...

 

[chrisbray]

I'm eyeing IL for a sleeper play. Both NAMs seem to be keen on upwards of 2k cape working up towards chicagoland and decent shear, but I will wait for the RAP to chime in and how overnight convection plays out and check back in during the morning...

Ok, I am thinking if cloud cover can erode and we get some decent heating along the IL/IN border it could be a decent day. RAP doesn't think we will even break 1k cape but NAMs still think so. Unfortunately I am inclined to belive the RAP as the NAMs seem to overdue cape every setup. We do have plenty of moisture in place already, with mid-upper 60s dewpoints, and a low pressure system passing close by, with some decent helicity. Give me a bit of sunshine to boost weak lapse rates and who knows...I can see SPC agrees there is a chance, 2% baby!

 

[Ben Holcomb]

The last couple runs of the HRRR (and maybe further back) are supportive of my thoughts of multiple storms blowing up along the dryline from about the red river and south in Texas. I'm going to head out here soon for a target of south of Wichita Falls, perhaps Seymour. There appears to be decent convergence about that far west per sfc obs with upper 60 dewpoints to the east and a somewhat diffuse dryline to the west along a US83 line or so.

 

[Jeff Duda]

I was pretty weary of the 00Z NAM solution last night because it progged Tds > 70 from I-40 southward with temps exceeding 80, and int many parts of TX, 85 F, during the afternoon. That's about the same forecast as the 00Z NAM from 18 May gave for last Monday (the day that prompted the now infamous EF4/5 tornado forecast for OKC from someone who will not be named). That forecast also horribly oververified, as dewpoints across much of OK failed to get into the mid-upper 60s. Consequently, convective activity was very limited, and generally non-severe. As expected, the 12Z NAM and its various flavors have significantly backed off on the moisture quality, and to some extent, the heating, this afternoon. I believe it now has a much more realistic forecast.

With that said, it looks like you'll have to be at or south of the Red River to get into the truly juicy air with up to 5000 SBCAPE, which, based on lapse rates from morning soundings or, in the case of DRT, already present at 12Z, looks to certainly be possible with theta-e values getting up past 350 K. I think the big weakness with this setup is the marginal mid-level flow and lack of any sort of LLJ progged to happen as the evening sets in. This is resulting in marginal deep layer shear values. However, with such extreme levels of instability, it certainly could be one of those days where a few dominant storms could alter their meso-gamma-scale environment and do some pretty impressive stuff before joining a convective cluster or just petering out. Low-level shear is not impressive, but the rule is that once there are multiple storms in an area, you can throw out the book on low-level shear. All it takes is one storm to ingest an OFB from a nearby storm and you'll get yourself a tornado.

I have an appointment early in the afternoon. If I can get done with that in time, I will make an attempt to get to NW TX. Deviant storm motion looks to be largely E or just south of due E, meaning if I can't get down there in time for initiation, I may have some trouble catching up while storms are still in their prime.