2017-05-27 EVENT: AR/KS/MO/OK/TX

[Brian McKibben]

Overview

Westerly flow at 500 mb and lots and lots and lots of surface moisture = Severe Weather!

Surface

It is going to be down right soupy this weekend. Moisture returns starts on Thursday. The northern gulf is not looking good right now. However, since the gulf doesn't get cleaned out we see very nice moisture return by Sat with dewpoints possibly into the low to mid 70s (I don't think we will see upper 70 Tds like GFS is forecasting). Nevertheless we could see extreme CAPE values. Sounding below paints the picture. I doubt we get 6,500 MLCAPE, but >5,000 MLCAPE is not out of the questions.

After no real defined dryline on Fri it looks to sharpen by Sat and sets up east of I-35 by 21z. Theta-E values will be off the charts with 370+ K throughout the warm sector.



Upper

50+ kts of WSW flow at 500 mb should be good enough to yield decent 0-6km shear aoa 40 kts. So we should at least see some supercells initially. Plus there is decent veering in the wind profiles. 850 mb flow is modest (aoa 30kt) at best and a little too westerly for me. But it should be enough to do the trick.

Conclusion

I don't expect a tornado outbreak, but I do think we could see a monster tornado with any discrete cell. The amount of instability alone will cause extreme stretching of the updraft and there is enough 500 mb flow to get that bad boy titled. Plus I don't see the CAP being as strong on Sat as it is on Fri, so we should see storms fire.

There are a number of high cape marginal shear events out there to compare this event to. I can think of 2 such events that resulted in F4 tornadoes. I would just plan to be in place at initiation because you could get no storm to tornado in less than 45 min.

Special Treat

It would be neat to see a storm work with this much potential energy. It would look like a bomb going off. 8,000+ SBCAPE and 6,500+ MLCAPE. That would be insane to say the least. Of course this sounding is cherry picked.

 

[Trey Thee]

Just waking up and check the 06Z runs. I still have some concerns about storm mode. Looks like we could see some storms go linear or have multiple linear segments which will make viewing more difficult and will possibly limit the tor threat. It does seem that there is going to be a substantial hail threat over good portion of eastern OK and NW ark and including SW MO.

Flow could be a touch better directionally and wind speed is somewhat lacking IMO. While still adequate it's far from a slam dunk. If cells can stay discreet we'll see a couple of strong tornadoes, if things go linear quickly we'll have embedded tors and/or tail end charlie situation.

Interestingly and frankly, surprisingly, the models continue to be in general agreement of mid and UPPER 70s TD's and the latest NAM has a couple of tiny spots of 80 in eastern OK. Instability while perhaps not getting to 7,000 or 8,000 J/kg will likely be 5,000ish the way it sits now, that is substantial.

Frontal location among other surface features still need to be better resolved but it definitely looks like we'll see some significant severe on Saturday. Though I'm still not sold on a high tor risk at this point.

 

[Dan Robinson]

It does appear that storm mode is going to be key on this day. I didn't look exhaustively everywhere, but all of the forecast soundings I looked at across MO, OK and KS have that huge CAPE uncapped by 21z. Anything discrete is going to be a beast, even in the open warm sector. Outflow boundaries from Friday and the synoptic front are the obvious players if things don't line out instantly.

 

[Ethan Schisler]

As of looking at things right now, I would probably target Southeast Kansas into maybe Southwest Missouri. It depends on if this thing backs up or not and gets pushed further west into the better terrain. Anyway, I think storms could go early in this area especially if there are any outflow boundaries and with as much instability in place, I could still see a few tornadoes occurring despite any early intiation or upscale concerns. Obviously the more discrete storms are, the more significant the event is, given the parameter space we are working with here.

 

[Dan Robinson]

4KM NAM Nest seems to be setting up a derecho event across KS-MO-IL with the MCS already going strong in central KS Saturday morning. Hard to see that dissipating much with the downstream environment in place.

 

[Ethan Schisler]

Agreed....it appears as though this is going to be tough event as far as forecasting and chasing goes. Might be worthy to set up ahead of that MCS after-dark here in IL and watch the lightning. With 6000+ CAPE....there should be plenty of it.

 

[Jeff Duda]

I wouldn't be so quick to dismiss forecasts of solid mid-70s dewpoints with embedded spots in the upper 70s. We're in late May and it's been pretty wet across much of OK/TX lately, so not only will advection from the Gulf help, but ET from the ground will as well. Now, I don't think we'll see much above 18 g/kg 100-mb mean mixing ratios, but a skin deep super moist layer hitting 77-79 is not at all out of the question. The SREF suggests strong potential for mid-70s dewpoints to verify across E OK and W AR, and ensemble max values approach 80 pretty much everywhere.

 

[Trey Thee]

I wouldn't be so quick to dismiss forecasts of solid mid-70s dewpoints with embedded spots in the upper 70s. We're in late May and it's been pretty wet across much of OK/TX lately, so not only will advection from the Gulf help, but ET from the ground will as well. Now, I don't think we'll see much above 18 g/kg 100-mb mean mixing ratios, but a skin deep super moist layer hitting 77-79 is not at all out of the question. The SREF suggests strong potential for mid-70s dewpoints to verify across E OK and W AR, and ensemble max values approach 80 pretty much everywhere.

Jeff a few days ago I was pretty skeptical of the mid 70s dew points, but model agreement has been really good and models have trended from mid 70s to now some upper 70s showing up. Seems that mid 70s is likely if not upper 70s, as strange as that sounds. Monster CAPE and a huge hail potential look to be the biggest threat based on what I'm seeing on the 12Z runs.

There will be a tor threat but it may be reserved for bottom of line segments or any cells that can remain discreet. Low level flow looks less impressive on 12z than it did on 06z and then it was not great. Obviously lots more to resolve between now and Saturday but this looks to be a really massive hail threat, with perhaps a 10% tor threat.

 

[JamesCaruso]

I am really not interested in chasing OK east of I-35. Despite the terrain, I might chance it just to see the explosive convection, but considering I will be chasing CO on Friday, the terrain in eastern KS/OK is just not worth the trip if it's even in range. Really haven't looked at much data yet, as I am just flying out to DEN tonight and at the moment focused more on tomorrow (Friday 5/26). Just looking at the dew point map above, I was hoping there might be a play in southwest KS where the moisture wraps in around the dryline/front intersection, but it looks like the cold front is surging southward so that's not going to work. Would also worry about the southwesterly 850 winds and looks like some veering of winds in the warm sector as well.


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[CGardner]

The winds just don't scream at me to chase. I'm staying home........in SE Kansas. Probably won't have to go far anyway.

 

[Randy Jennings]

One thing that has caught my attention about this day is how little the GFS has changed from run to run in north TX and OK. It sure has been consistent in firing storms with TOR soundings. Now it may be consistently wrong, as the NAM keeps saying no precip (although it hasn't been in range long) and the GPDS can't make up it's mind. Run to run consistency is a good sign.

 

[Randy Jennings]

The 20170526 06z GFS is sticking to its story that the cap breaks along the dryline in OK and north TX and we get storms. 3k NAM says it doesn't. NAM say it doesn't but is close. When you look at the NAM and 3k NAM run-to-run trend you do see some differences in CIN along and ahead of the dryline, but they are still pretty minor.

Another interesting thing to me is the T and Td's the models are predicting. For example, the GFS has T/Td at 90/80 at 21z and 85/80 at 0z near Okemah, OK (along I-40 east of OKC). The 3k NAM was even cooler but just as moist (80/78 and 83/79) Is the Td going to be that good (this AM's observed soundings are in the mid-70's on the south TX coast)? Are the models understating the temps? My gut says we could have a larger Tdd and higher LCLs than the models are predicting. On a side note, the GFS soundings for that location at 21z/0z are TOR/PDS TOR and the 3k NAM is None/SVR.

Given I live in DFW I guess I'm going to stay at home, monitor things, and head to the dryline if it looks like the cap is going to break. But I'm not going to hold my breath.

 

[Tim Paitz]

The NAM 3km has been quite consistent with a bow echo surging east ever so slightly south of I-70 in MO but recently it's been trending a tad bit further south (and the bow echo itself is a tad bit smaller).

 

[Tim Paitz]

Agreed....it appears as though this is going to be tough event as far as forecasting and chasing goes. Might be worthy to set up ahead of that MCS after-dark here in IL and watch the lightning. With 6000+ CAPE....there should be plenty of it.

It looks like that bow echo might cross the Mississippi between about 00Z-02Z tomorrow evening. The models have been pretty consistent with that.

 

[James Wilson]

There is an outflow boundary on the Kansas Oklahoma border that will probably be the focus of my attention today.