Confidence growing in severe weather event tomorrow evening

Well, I'm gonna have to bite again, even if the apple is snatched away at the last second, because the models have changed their tune big time. I no longer think we're going to be capped on Thursday night/Friday morning, and we could easily wind up with a nocturnal MCS if not a true derecho plowing across the state.

Some of the instability levels being forecast by the SPC ENSEMBLE - not just one model but the weighted average - are on the order of 3000-4500j/kg MLCAPE. That represents an EML plume; an "elevated mixed layer". The "mixed layer" is the area in the atmosphere where all the action takes place. This is the area is the battlefield where the war between warm and cold air is fought. The 'deeper' the mixed layer - that is, the more vertical space on the battle field - the more carnage can take place. The mixed layer is considered "elevated" when it reaches very high up, is particularly deep and very unstable - lapse rates (temperature of air as you get higher) tend to be steep. Such conditions usually result in a weak cap at the lower levels of the atmosphere which prevents thunderstorm activity until peak heating. This is when you can get the explosive growth of supercells and severe multicell clusters depending on how favorable wind shear is for said development. 

Bulk shear of 40-50kts should be more than enough to drive explosive thunderstorm growth, and most of the models are coming in with supercells developing into an MCS over the upper peninsula in the late afternoon. This will drape southward across the lower peninsula by late evening/overnight, likely bringing a significant damaging wind threat.

I do see our probabilities going up if this forecast continues to show up as is over the next day, so make sure you're spending tomorrow night in substantial shelter. As I've had a bit of an active week, I'll do my best to keep everyone posted about this. I don't think lack of sunshine is going to shut off the severe threat this time around, as this system is fueled by the torrid heat and humidity settling in over the central US, and actually looks like it'll be on the powerful side.