What Happened Wednesday, May 11?

[John Hudson]

Things were looking so good for decent storms to pop in SC Kansas on Wednesday, and I was in my hotel room in Wichita on Tuesday evening planning on at least two days worth of good storms to chase.

On Wednesday morning, everything just seemed to fall apart, and I am trying to figure out why everything went to Hell in a handbasket. I watched many storms form what seemed to be quite robust updrafts that just fell apart before they could get organized, and just can't seem to get my head around what went wrong with my forecasts.

My initial suspicion was that it was a classic cap bust.

Any thoughts/input from the pros would be, as always, highly appreciated.

John
VE4 JTH

 

[David C Watson]

Well for starters, there was an early morning crapvection event that started in TX and went all over OK and left behind atmospheric debris/cirrus canopy plus, there were still ongoing storms in OK/TX that kept the atmosphere from fully regenerating and allowing the sun to heat the atmosphere thus, allowing CINH to take over and successfully capping off the atmosphere.

 

[Ben Toms]

It was much, much more than a classic cap bust. Although that morning convection did completely demolish the set-up, that wasn't the ultimate cause. There was actually an even bigger problem with the day that lead to that crapvection - the shortwave that was supposed to help kick off our storms ejected about 6 hours early. Even if the morning convection hadn't been sparked off by this, the day would have most likely not owned up to what it was supposed to be. There probably would have still been storms, but with less forcing the overall threat would have been reduced.

The main issue with the morning convection was that not only did it clear out all of the already built in instability, it also towed away all the moisture. An outflow boundary followed the precip up into NE KS/SE Nebraska, switching most of Kansas's surface winds to westerlies. This obviously cleared out the moisture and resultant instability in addition to creating issues with redeveloping a moist warm sector. Yes, we got the heat later in the day, but the moisture just didn't return like it should have. Mid to high 50 DP's are significantly different than mid to high 60's (especially when temperatures rise to about what is forecasted).

So, overall, the day was just a complete bust. I'm still not convinced that sub-tropical wave didn't have something to do with our main wave ejecting early...

Comments on my observations?

 

[Jeff Snyder]

As others have noted, I think the widespread convection in the morning and early afternoon was the primary culprit for the lack of intense convection later in the afternoon and evening. The widespread convection created extensive, relatively-low theta-e outflow across central and western Oklahoma and adjacent portions of southern Kansas. Given the pressure pattern across the Plains, this low theta-e air then advected northwestward into Kansas. As soon as convection redeveloped in far southwesterly Oklahoma between 12 and 1 pm, it became increasingly clear that appreciable CAPE was unlikely in much of the previous target area; the SPC downgraded to SLT / removed the MDT before this time, which (obviously in hindsight) was a good call.

Of course, it didn't help that widespread upper-level cloud cover (associated with anvils) spread over most of central Kansas and Oklahoma on S or SSE upper-tropospheric winds, reducing insolation, keeping temperatures relatively cool, and inhibiting more significant destabilization. Some heating did occur along along a narrow zone between the dryline and western edge of the anvil canopy, but, with the lowered Tds, CINH remained high enough to inhibit convection.

Below are 00 hr analyzed MLCAPE and MLCINH from the 00z NAM from Wednesday evening.
MLCAPE analysis
MLCINH analysis

A couple of storms did try to develop around DDC, but the thermo environment wasn't particularly impressive (around -60 j/kg CINH, < 1000 j/kg MLCAPE, 1500 m MLLCL, etc.). In addition, looking at the hodograph, storm structure may have been messy even if sustained convection did occur. Even the 58F Td and 74 F T in this sounding were very shallow. Cold mid-level temperatures (-15 C at 500 mb) still yielded pretty decent CAPE for the 74/58 parcel, but that would not have characterized the mean inflow parcels characterizing the updrafts in any storms in that area.

Looking closer to Oklahoma, this is the Alva 00 hr fcst sounding from the NAM. The stable low-level environment is very evident. In addition, it looks like the upper-tropospheric flow is quite a bit more backed than forecast (of course, this may be the result of adjustments from the large area of convection in central Oklahoma through northern Texas).

Edit: Changed some of the embedded images to links to reduced the length of the post.

 

[jshields]

the winds didn't switch to the west to keep away the moisture and high dewpoints. that huge mcs that moved through killed everything. first there were storms and rain that came though early in the am through kansas. then you had the huge area of rain and storms that moved through oklahoma and texas the rest of the afternoon. skies actually cleared quite a bit in kansas which got me excited, but then the high cirrus moved in from the blow off of the anvils which hurt heating. the storms to the south also killed the moisture flow as well. the winds were actually fairly strong gusty to 25 mph out of the south and southeast over most of western kansas, but the winds were blowing in modified air off of the storms to the south, so the atmosphere never had a chance to recover.

It was much, much more than a classic cap bust. Although that morning convection did completely demolish the set-up, that wasn't the ultimate cause. There was actually an even bigger problem with the day that lead to that crapvection - the shortwave that was supposed to help kick off our storms ejected about 6 hours early. Even if the morning convection hadn't been sparked off by this, the day would have most likely not owned up to what it was supposed to be. There probably would have still been storms, but with less forcing the overall threat would have been reduced.

The main issue with the morning convection was that not only did it clear out all of the already built in instability, it also towed away all the moisture. An outflow boundary followed the precip up into NE KS/SE Nebraska, switching most of Kansas's surface winds to westerlies. This obviously cleared out the moisture and resultant instability in addition to creating issues with redeveloping a moist warm sector. Yes, we got the heat later in the day, but the moisture just didn't return like it should have. Mid to high 50 DP's are significantly different than mid to high 60's (especially when temperatures rise to about what is forecasted).

So, overall, the day was just a complete bust. I'm still not convinced that sub-tropical wave didn't have something to do with our main wave ejecting early...

Comments on my observations?