Today's surprise severe weather, and coming weekend potential

Early this morning, the US convective outlook issued by the SPC looked like this:

By around 9AM, it looked like this:

And by 12:30PM, it looked like this...

...and there was a mesoscale discussion issued for the southern half of lower Michigan indicating a 60% chance of a severe thunderstorm watch.

This is one of those days where nature threw a curve ball, and it has me a bit concerned for what's potentially on the horizon this weekend. 

For starters, I did not see this one coming in the slightest. I'll grant that today has been especially busy and that I didn't get to stop and look at the models this morning as I normally do, but even if I had, chances are I would've agreed with the SPC's outlook. The models - even the short range ones - laid a big goose egg on this one. By 12:00PM it was becoming clear that conditions were a bit more favorable for big storms than originally expected, despite marginal instability. This had to do with a storm system that had strengthened, and the strong winds aloft making up for the lack of instability. In all, we had about four or five severe thunderstorm warnings today if memory serves me correctly, with some decent tree/power line damage reported in about 6 or 7 locations from Twining in the north to Evart in the south.

So why am I concerned?

Well, the models, to put it bluntly, are sucking the big one lately. Forecasts are all over the place. Mr. Torregrossa made an entire article to point out that the weekend temperature forecast looks hokey at best. I agree with him to a point - the temperatures being forecast have been all over the place. However, there has been some consistency on a couple of things, and those things have everything to do with storm potential. The first have been the dewpoints and amount of moisture being predicted. Humidity should be on the increase as the week draws to a close. The models (both the Euro and the GFS) have placed the amount of moisture in the forecast to be quite high, and have been fairly consistent about this. Regardless of just what temperatures are actually achieved, we can assume that it's going to be quite humid - dewpoints of 70°F or higher are going to be possible per both models. The other aspect that has been fairly consistent has been the winds. The latest forecasts placed bulk shear excess of 50kts. That means that wind speed is forecast to increase by 50kts+ from the ground to the mid-levels where the tops of the thunderstorms are located. That amount of shear alone is enough to produce severe thunderstorms. You may have experienced some of these shear-powered thunderstorms today, as this was the primary ingredient for the small event that took place.

So in looking at today, we're seeing how lack of instability caused guys like me (and apparently a few people over at the SPC) to get caught off guard. Let's see what a situation like this with some added instability could look like:

Let's look a bit closer:

And even closer. Let's look at Pigeon:

Good? How about Caro:

Helicity, CAPE, bulk shear, critical angles and all these wacky technical terms and graphs aside, none of it means jack if we don't get thunderstorms. However, one of two things coming from the north could cause them - a dry line or a backdoor cold front coming from the northeast. I'm especially worried about the latter. Storms would just explode - EXPLODE - in an environment like the one depicted above if any kind of boundary were to interact, but a cold front would serve to turn a few explosions into a full-scale nuclear strike. The mode would initially certainly produce supercells and tornadoes, which would then merge into a line to become a potential serial derecho. The tornadic threat would then be replaced by one of hurricane-force straight line winds. I don't have to mention that the hailstones alluded to in the graphs above would be apocalyptic on their own.

So how does one call this, with the models being as frenetic with the forecast as they've been? I'm not sure yet. I'm leaving my outlook as it is for now - with "severe likely" as my official opinion. As is always in Michigan, this is likely to be an all-or-nothing thing, where we'll either see a horrendous event on the order of June 22nd of last year (or potentially much worse), or absolutely nothing of note. If you want the big storms, pray for levels of moisture/shear currently being forecast and a boundary to go with them. If not, pray for the opposite. My opinion is that differences in temperatures are going to have somewhat of a negligible effect on this should the amount of shear crossing the area be what it's predicted to be. Fuel is fuel, but a motor is a motor, and when you have a fully-loaded twin-turbo with over 400 horsepower, you could only have a quarter of a tank and still be off to the races.