I'm not sure I'd have gone as far as to issue this outlook just yet. Considerable uncertainty remains regarding some fairly crucial details, not the least of which is capping. While there appears to be ample instability forecast, recent trends show that can be very misleading. There's some indications in the latest models that storms would develop to our south and east over Ohio and Ontario, but completely ditch Mid Michigan once again. Nonetheless, ample moisture should be present at the surface and models do show 850mb dewpoints recovering by 5PM. I'm going to fall in line with the SPC for now, though I'm somewhat skeptical. I could see this outlook falling back to marginal by tomorrow morning.
Thinking positively, this storm system is forecast to suck up quite a bit of moisture from the Gulf this time around, to the tune of 2 inches+ of precipitable water. PWat is a great measurement of rain/thunderstorm potential. If all of the moisture at a given point were to fall as rain, it tells you how much would be available. Once you start getting into values above 2 inches, you're dealing with a very rich, well-fueled storm system. The system in question does appear to be a bit more impressive than what we've dealt with so far this year, at least in terms of moisture and position. The center of a fairly strong closed low is forecast to be present over extreme eastern Manitoba/western Ontario, which is a great place to produce thunderstorms in mid Michigan. We're going to be well into the warm sector, with temperatures again shooting for 90°. The upper level support appears to be quite strong, too, with 250mb winds forecast at 90kts+ just to our northwest. I'd be a lot more concerned if the strength of the low-level jet was higher. As it stands, 30-40kts of bulk shear is the best we're going to have. This should be sufficient for a damaging wind and hail threat in any areas where thunderstorms do form. The tornado threat right now appears small.
My hope is that some convection is able to form this time and we can tap into some of that rich moisture rather than watching it all go to waste again. This state is quickly approaching the point where problems could occur if we don't get some good, widespread rain soon. Unfortunately, in the interest of pure honesty, despite very consistent model guidance, I'm not that confident in this forecast. Too many limiting factors remain in question for me to be liking this, such as capping/subsidence drying and just what kind of mid-level lapse rates we're going to be dealing with. The models have been vastly underestimating capping potential this year, which is one of the reasons they've been so hokey. I'll be more confident if I see a few models showing adequate storm coverage Sunday over Mid Michigan over the course of the next two days.
UPDATE: I'm a little more optimistic after seeing the 12z NAM4KM simulated radar, shown below. This shows either two semi-discrete lines or one semi-discrete broken line which would pivot through the area, bringing a good bit of rain through most of the Thumb. When I've seen this before it tends to indicate a phenomenon called "training" which can lead to a LOT of rainfall - storms form one behind the next like train cars, and douse the same areas over and over. Normally this would concern me for flash flooding potential, but as dry as we are, I can only say, "Bring it on!" Hail/damaging winds/isolated tornadoes would appear likely in this storm mode, too, validating the slight risk, but it'll be worth it if it means not going up like a powder house on the Fourth of July, and if we can have some vegetables in the fall.
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