4/5/10 DISC: KS and MO

[Winston Wells]

Keeping in mind that we should always try to learn from busted chases, could I ask our more experienced chasers and forecasters to offer their views on why thunderstorms failed to initiate before dark yesterday (Monday, 4/5/10)?

Was it simply a capping issue, or were other factors involved as well? Were different inhibitors at work over the eastern Kansas/dryline target as opposed to the northern Missouri warm front play?

Thanks in advance for any help here! (I gave up yesterday in Kirksville, MO, but I did enjoy briefly meeting Ben Holcomb and Illinois chasers Jesse Risley, Ryan Wichman, Brandon Sullivan and Adam Lucio in Macon. Mods: please move if this belongs in the Post-storm Discussion area).

 

[John Farley]

I had a rather frustrating experience yesterday of leaving the one area where a tornado did occur (southwest IL) to head for northern MO. In fact, I even saw the "storm" that eventually produced the tornado when I stopped for gas about 10 miles from my house, as it passed just west of the gas station where I stopped at I-270 and Lilac in north St. Louis County, MO. (I say "storm" because at that point it did not appear to yet have any thunder and lightning.) It had a nice appearance, though, with the precipitation downshear from the hard, round updraft base, and even formed a couple small lowered areas right under the updraft. It was calling out "chase me" - but I did not, because if I did, I would not be able to make it to my target area in northeast/north central MO in time for expected initiation. Later this little cell intensified, getting first a SVR warning then a TOR. It produced the only daytime tornado of the day near Hillsboro, IL, as well as golfball hail. But by then, I was 100 miles or so west, staring at blue sky in MO.

One factor, I believe, in the storms developing from IL eastward was that the instability ended up being better in that area. While the forecast models showed improving instability westward across northern MO, the actual instability was higher in southern IL and eastward, with CAPE around 2500 by mid afternoon. I think that is one reason that supercells developed along that part of the front but not farther west in MO. I'm sure capping was also an issue in northern MO, and there may have been others. The models never broke out much precipitation in that area (which verified), but they also showed better instability there than farther east, which did not verify.

 

[David Wolfson]

My perspective of my busted "forecasts" is that the models were off-and-on a bit hopeful about the amount of moisture available. Surface DPs were generally in the low 60s and not as deep as expected. This pushed the convective temperature up into the mid-upper 80s, which just didn't happen east of the dryline, being early season and all. Plus the upper forcing was a little slow and further north so the lee cyclone didn't deepen much in the early afternoon. That kept the winds more veered from the west so a better stream of moisture wasn't drawn back into south-central KS. That action started late and was pretty puny; the stronger cap won out over western OK near nightfall.

 

[Dave Kaplow]

IMO the most interesting thing about yesterday was that it was not really a complete blue-sky cap bust. Deep convection did eventually initiate in northeast KS right before dark, but well behind (west of) the radar feature we assumed was the dryline. Why there? Why then, and why all at once along a line? To my knowledge there was no specific boundary exactly where the line of storms fired, and no special triggering mechanism other than increasing upper support. Is that simply all that was needed at that point, or am I missing something?

Edit: I guess I should add that I'm aware the storms were along a somewhat diffuse stationary front, I guess what I'm really asking is, was there also an outflow boundary in play that I was unaware of, or some other kind of non-obvious focusing/lifting mechanism?

 

[Ben Holcomb]

Nice meeting you yesterday, Winston.

The one thing that really concerned me all day was the fact that Missouri was socked in clouds most of the day. We never managed to clear out and get some daytime heating like we did today in Iowa. That's definitely something that could have helped - more heating/higher surface temps to overcome the cap.