2011-05-23 FCST: KS/OK/TX

[Tim Supinie]

Surprised no one has started a thread on today yet. SPC put out a small moderate risk in north-central Oklahoma on the 1730 UTC outlook yesterday, but removed it on the 0600 UTC outlook, citing the potential for morning convection to mess up the day.

Nothing on the radar yet, but a cursory glance at the water vapor reveals a subtropical jet streak and slight shortwave troughing across northern Mexico south of Arizona and New Mexico. This could be the trigger the SPC is referring to for morning convection.

I believe there will be some effect of the convection in north Texas and southern Oklahoma this evening on the convection tomorrow. The synoptic flow is currently advecting the outflow from those storms northward into southern Oklahoma, which may be the reason for the currently observed upper-50's/low-60's F dewpoints in central and southern Oklahoma. It appears that the NAM may be picking up on this, whereas the GFS isn't. The NAM has a definite boundary draped across central Oklahoma, south of which dewpoints are in the 70's F , and north of which dewpoints are in the upper 60's F. The GFS brings 70+ F dewpoints all the way into southern Kansas by 24/00Z. My gut is to go with the NAM, since it has a better handle on the current moisture situation than the GFS does.

As for a lifting mechanism, besides the surface dryline (roughly along the Oklahoma/Texas Panhandle border) and the boundary mentioned above, the NAM suggests shortwave ridging, whereas the GFS is slightly more neutral with the contours. However, both suggest slight height rises during the day tomorrow once the initial jet max exits the area, which pose trouble for any convection trying to develop afterward.

Neither the GFS nor the NAM develop spectacular wind fields, though the NAM does develop 0-3 km EHI of 10+ across northeastern Texas by 00Z. However, this is along and just south of the boundary mentioned above, which is roughly east-west, so should there be convection, there might be problems with convection stepping on other cells and nothing being able to get organized.

Of course, if the morning convection develops like the SPC believes, all this goes out the window. In that case we get into a situation like on 11 May, where we wait around and look at observations to see where the best place to head would be. I hope this doesn't turn out to be like 11 May, or I will be waiting around to see what Tuesday holds.

Right now, as always, the plan is to look around in the morning and see what happens. Southern Oklahoma is a likely target tomorrow, but this will probably change.

 

[Ken Johnson]

Looks like morning convection will not be a problem today
RUC develops extreme instability along and east of the dryline. Still no signs of wide spread convection, but rather isolated supercells. Low level shear isn't spectacular, but with extreme instability, combined with stronger flow aloft, could be enough to trigger a few twisters.

 

[Tim Marshall]

will head out to western Oklahoma today, probably Sayre area. I like the "day before" scenario with the dryline moving out only to the TX/OK border (per RUC)and a weak surface low around CDS which helps back the winds across western Oklahoma. However, I remained concerned about the weak 700mb flow (HP)and the east-southeast upper flow where anvils rain into the low-level inflow.

 

[Tim Vasquez]

At this point we're transitioning a bit into post-forecast analysis but instead of starting a MISC thread I figure I'll tag this on here, and I can't add much since I need to go make dinner.

One major thing that stuck out for me was the exceptional instability, as seen here. We often hear about 3000-5000 MUCAPE on a storm day, and a lot of times those numbers seem spiked depending on where they come from and how they're generated so I often don't pay any attention to them. But it looks like on this day we got some genuine high instability. Here the CAPE has been worked out with an approximate parcel for what these storms are ingesting right now: that's in the 4000-5000 j/kg ballpark, so definitely some major instability at play here.

The big problem of course here is the mid-level wind weaknesses, as Tim M pointed out. Plotting the mean nonsevere motion as a blue dot places it right on the hodograph trace. So storm splits were obviously a big problem, especially early on in Garfield, Major, and Blaine Counties. However with this amount of instability, the presence of a strong cap, and the boundaries not being too "cold", the storms eventually pulled through into relatively isolated cells as heating diminished.

I saw that we were under the influence of weak short wave ridging today, which is one reason why the cap had strengthened and winds started out kind of veered. However in the end they did manage to back a little more than expected.

It's interesting when you compare this to what the HRWW was expecting. It was over-aggressive with the precip, so some of what is shown here in W OK is actually outflow, but in the untouched moist sector it was not indicating much backing at all along with a little more moisture erosion (near the dryline) than we actually had. I haven't looked at the other models today, but I notice the HRWW does not seem very responsive to mesolow or heat low development (or whatever combination of ingredients led to pressure falls out west). I noticed this tendency the past few days also (and fortunately anticipated it). To me the forecast wind fields are the single most important part of the mesoscale models, so I'm always interested in what they have to say.