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.