The main reason for this lack of any severe risk is going to be timing. Thunderstorms are looking as of now like they'll come through in the morning hours, and they won't have much instability to work with. By the time the real conditional instability builds in during the afternoon, all the convergence - the "forcing" of air upwards by fronts - will be removed from Michigan. This is a "loaded gun with no trigger" scenario.
You can think of a thunderstorm as a car - the more severe the storm, the more horsepower it has to work with. Good severe weather is like a Lamborghini. In order to run at its full potential, it has to have plenty of open road to work with (a clear day where nothing really gets off the ground until peak heating usually due to weak to moderate cap in place), and plenty of premium fuel in the tank (instability). The engine has to be in good condition (high winds aloft). Most importantly, however, the vehicle has to have a functional ignition switch/starter motor to get the engine running. That ignition of severe weather is usually caused by a cold front or outflow boundary (miniature cold front caused by rain cooled air in the wake of a previous thunderstorm) that pushes the warm air upwards and the cold air downwards - convergence and divergence, respectively.
A supercell thunderstorm would be when the Lamborghini really gets going, and a tornado is when it starts to burn the nitros. With the sounding shown above, both would be possible on a day like Friday, but there's one problem - there's no key in the ignition. Without adequate lift to push the air upwards, the car isn't going to start.
With that in mind, this is Michigan, so there's a couple more things to consider. Air cooled by the Great Lakes can also serve as a mini cold front, and can even enhance wind shear. This is a phenomenon known as a lake breeze, and it was a big factor in the thunderstorm that produced a tornado in St. Charles near Saginaw last year. If such a breeze were to occur in an environment like the one pictured above, considering how weak the cap would be, we could see the formation of severe thunderstorms even in the absence of a cold front. This sounding also has significantly more left-to-right movement than the soundings that were forecast by last night's runs, so said thunderstorms would likely rotate. Several things work against this scenario, though. The first is that this is only one model predicting one possible outcome; others are more modest in what they suggest in terms of wind shear. The second is that even if all the conditions line up the way the NAM is predicting them, timing would need to be absolutely perfect for this to occur - the window for the lake breeze to have an impact would be very small. I'm not so sure I even buy into this scenario at this point, as early-day thunderstorms usually temper instability a bit, and this is looking a little crazy in that regard.
Regardless, I'd still say the risk for an isolated severe storm or two on Friday is present, but I'd also say it's very, very marginal. Keep cellphones and radar apps close if you go to the beach, but don't cancel your outdoor plans at this point.
No comments:
Post a Comment