Severe Weather Threat 3/2/12

What can I say? This has been hyped to epic proportions. People comparing it to 4/27/11 or 4/3/74. Calling it a major outbreak that will surely surpass 2/28-29. Ridiculous.

The truth is, winds are already veering:

Already SSW at the surface in the warm sector. And it’s all downhill from here. That’s the first thing wrong about this system. The trough is crap. The sfc low runs ahead of the warm sector. And sfc flow along the trailing front turns SW. Directional shear goes to nil.

It’s interesting though, that the models still paint notable parameters (CAPE/SRH/etc.) in the warm sector. Funny thing how the 2/28 threat was not so impressive in that aspect, but impressive in the synoptic setup. Here, the synoptic setup is crap, but the parameters are good. I have had notable successes going with the synoptic setup…but I have also have been burned ignoring the parameter space. But really, with SSW winds turning to SW over the warm sector, you’d have to pay me to issue a High Risk. The MDT looks good for now. And in fact, I’d only issue a 10% hatched torn risk, with the hatching concentrated closer to the sfc low where winds will be backed.

This is what my thoughts are. There are indications that as the LLJ intensifies overnight, it will spark off elevated storms north of the warm front…in fact it’s already happening now along two intensifying LLJ axes – one backing into MO and one veering into TN. These two will merge and clusters of storms will develop north of the WF along the OH River Valley. Now we have to watch these, because the cap is not particularly strong and the boundary layer is not particularly decoupled in the warm sector. Some of these storms, if they can back-build into the warm sector, may root to the surface and tap an incredible parameter space, while the sfc flow is still relatively backed.

The greatest threat for tornadoes IMO is around 12-18Z. We will have the parameters and the backed flow still and there will be storms out there that can tap whatever’s there. One possible caveat is that if a large convective cluster develops on the nose of the intensifying LLJ overnight, it could leave behind subsidence, and this is actually hinted on in some of the models. This would dampen any remaining tornado threat, for after 18Z, the sfc flow veers considerably north of the TN Valley. At the extreme end is the GFS – it would suggest the threat is over everywhere by 0Z. I am a little reluctant to say this, but I am not afraid to say that the sig tor threat will be diminishing by then.

As always, the usual disclaimers apply. Weather forecasting is a tough and unpredictable business.