Anticipating storm development based on what's happening vs. what the models predicted

So far, the NAM and other mid- to long-range models haven't handled the forecast very well. Even the short range models are having trouble with this system and predicting where storms are going to form. Take a look at this image:

This is a loop of simulated radar reflectivity starting at around 8PM EDT yesterday evening and progressing until right around 11AM. Notice that quite a few things are different at the end of the loop from what's actually happening right now:

First of all, there's no cluster of thunderstorms over Wisconsin. The blob of rain on the border between Indiana and Ohio is a bit further north than originally predicted, and has held together a bit better. Finally, there's a cluster of showers over western lower Michigan. Now, all of these features are quickly dissipating, however it tells you that the forecast wasn't very accurate in terms of placement of atmospheric activity.

The NAM model seems to favor a more east/west track of activity, while the HRRR is favoring a more north/south track. I think the sweet spot is somewhere in the middle, in which case I'm of the opinion that tonight's storms may affect the north portion of the state more than the south. In terms of new development, the HRRR definitely missed what erupted in Michigan, and if that happens tomorrow, it'll be more than just showers popping up. As such, I maintain the "severe thunderstorms likely" portion of the outlook for most of the eastern portion of the lower peninsula for tomorrow evening, and include the SPC's slight risk area. I think that otherwise the threat for severe weather is marginal at this point.

Weekend outlook is a bit clearer, but uncertainties remain

The upcoming weekend will almost certainly bring some severe weather potential to Michigan, but the jury is still out on how much. It's certainly not looking like another June 22nd 2015 anymore; both the NAM and especially the GFS have backed off a bit in terms of the conditional threat.

For now, the SPC has put out a marginal risk encompassing most of lower Michigan for Friday, and a very small slight risk area for Saturday. I have actually expanded this area to include most of southeast and some of the northeastern counties near the Saginaw Bay as some of the models are suggesting increased potential in these areas.

Instability continues to be forecast to be on the strong side. This instability matches the earlier forecasts in the week by the GFS. The NAM is especially aggressive with temperatures, predicting potential 90s on Saturday. I'm not so sure if this is going to pan out, but considering we've already hit 90° in some areas this year, it really wouldn't surprise me that much. The real kicker will be the dewpoints. Both the NAM and GFS are predicting ample moisture presence over the area to the tune of low-to-mid 70s dewpoints, which makes the temperature impact negligible in terms of thunderstorm fuel. Dewpoints that high are going to drive severe weather regardless of whether we're in the low to mid 80s or the 90s, though obviously if temperatures hit 90 we'll have a bit more fuel for the fire.

The system itself is somewhat of a strong one, too, but here's where the forecast has changed. Where as the GFS was predicting 50-60kt winds aloft, the models are now suggesting 30-40kts. This, in combination with less wide-angle windshear, definitely reduces the tornado threat, though I'd still say a slight risk remains. The biggest hazards will be large hail and damaging winds.

Timing of this system is going to be everything. As of now, we're forecast to get a glancing blow on Friday and potentially an MCS from Wisconsin or Minnesota on Friday night into Saturday morning. This means that the storm mode could widely vary between Friday and Saturday. If the system stays the current course, we should have at least some storms fire up in southeast Michigan on Saturday afternoon. Early day convection could suck up some of the energy, and slightly stabilize the mixed-layer, but there's nothing to suggest that it will as of right now. The only real inhibitor predicted thus far would be higher up near the tops of the thunderstorms, where NWS Detroit is predicting "height rises" (pressure increases) from the previous day's storms (in my opinion, this matters a heck of a lot less than the mixed layer). If storms come through overnight rather than early on Saturday, the energy on Saturday afternoon should be greater. If the system speeds up a bit, we could actually see more storms on Friday popping up right in our area, and less of a threat Saturday. This would be especially true for any tornado threat as a speed up would indicate a strengthening, deeper system and likely much more wide-angle shear like what was originally forecast.

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.

Marginal chance of severe thunderstorms today in Central/SE Michigan

Latest short-range model guidance is suggesting that strong thunderstorms should develop throughout the region today, and parameters are strong enough that the SPC has introduced an isolated severe risk.

One or two storms could definitely develop damaging wind potential, and surface winds should become strong enough that I wouldn't even rule out an isolated tornado or two.

The latest GFS run has the weekend's severe risk back in the forecast, so I'm not adjusting my weekend outlook for now. I'll continue to keep my eye on it, but as of right now I'd say it's about 50-50.

Widespread rain to cover most of the state within the next few hours

Still sunny here in the Thumb, but that's going to change in the next couple of hours:

This will give everyone a much needed bit of rain.

Next weekend picture starting to become more muddy

The GFS has backed off a bit on how much instability its forecasting for next weekend, but the ECMWF has stepped up to replace it, predicting between 2500-3000j/kg of CAPE even in the morning hours.

I'm going to leave the outlook how it is for now, but if things don't start clearing up a bit with the next day's model runs, I may just put up a big question mark again. So far everything this year has been a bust for this area, and I'm beginning to wonder just how reliable the long range models are going to be even when in agreement. We may be looking at a severe weather season that either vastly underwhelms, or blooms a bit later in the year. Everything seems to be going around us - either to the south and then up the east coast (as it's happening today and tomorrow) - or fizzling out prior to making it out of the plains. Thankfully some rain appears to be arriving today.

Target time for storms shifts toward next weekend

It's now looking more likely that severe weather could be on the way on Friday into Saturday rather than on Thursday.

Timing aside, the conditions look like they could be strengthening a bit. Each subsequent run of the GFS is predicting a bit more severe potential. The ECMWF is just getting to the point where it can see that far ahead, and so far it's not quite in agreement, but it isn't too far off, either. It's suggesting some pockets of ridiculously moist air in and around the region in the days leading up to the weekend, too:

The biggest reason for my concern is the consistency between GFS runs that has continued to indicate 1) very unstable conditions in/around the Great Lakes, 2) strong low level, mid level and upper level winds, 3) at least some convection developing over the area.

And then there's the appearance of the pattern itself:

This pattern may look familiar to those who remember August 2nd last year:

It's too early to tell in terms of potential intensity, but this forecast sounding is definitely eye-opening: