A fairly decent squall line may plow through Mid Michigan, SE Michigan Sunday afternoon

I'm going to go out on a limb and say that our chances for severe weather in Michigan Sunday are a bit better than they were on Wednesday.

Jet core wind speeds and tilt of upper level disturbance as forecast by the NAM's 8PM run

18,000 ft wind speeds as forcast by the NAM's 8PM run

First and foremost, we're going to be dealing with another negatively tilted upper level disturbance pushing into our area.  The NAM in particular is forecasting this one to be quite a bit stronger than the disturbance which affected us Wednesday, with a negative tilt already in place prior to the system affecting our area. This is in stark contrast to the forecast the name was giving us for the Wednesday event, where it never quite predicted to be as robust as the GFS did, and when the system only took on a negative tilt after it began to affect us.  This time around, the NAM is predicting a much stronger cold front and upper level wind pattern, as shown above.  Hodographs are looking a bit curved/kinked on this one, too, meaning there could be enough shear to produce some severe weather and possibly even supercell thunderstorms.  Right now, the winds aren't looking particularly fast, though, so it's still quite questionable.  The timing of this thing currently looks really good to produce severe weather.  The cold front should be coming through in the late afternoon/overnight, driving storms during peak heating time. 

Simulated radar as forecast by the NAM4KM's 8PM run.

The result of all of this may be what the NAM4KM model is predicting - the formation of a strong squall line over western Michigan tomorrow at around 2PM EDT, intensifying as it moves eastward across central and SE Michigan.  This is the best evidence so far of problems, as a single round of storms has a better chance of producing severe weather than two, as the fuel tank will only have one straw in it.  Wednesday included widely scattered storms popping up in different locations throughout the afternoon, which served to drain some of the energy available for storms that formed later in the day, in a more favorable environment than what was there initially.

The biggest factor is going to be how much instability develops over Michigan. Enough instability should exist for severe weather, but right now it's still looking fairly modest.  If more instability develops than what is currently forecast, we may wind up with an even bigger severe risk.  Mid level lapse rates are, like Wednesday, currently predicted to be modest. This could be offset by enough surface heating tomorrow causing SBCAPE to climb to extremes. The chances of this happening isn't particularly great, but with enough of a warm sunny day, it is possible.

On a scale of 1-10, with June 22nd being a 6, August 2nd being an 8 and Wednesday being a 2, I'd say this sits at about 3 or 4 right now.  It could go in either direction depending on what the observations look like in the morning. The risk of hazards associated with the storms primarily favors damaging winds, as lapse rates look to be too modest to support large hail, though I'd not rule out a tornado or two with the curved wind profiles and negatively tilted cold front.  The line also looks as though it could be semi-discrete, which could wind up making the tornado threat greater than zero.