First, the bad news. The latest GFS and ECMWF runs are predicting a series of storms striking over the course of next Tuesday, Wednesday, Thursday and Friday. This would be two to three storms semi-congealed into one long-duration precipitation event. The ECMWF and the GFS actually forecasting complete opposites in terms of precipitation types. I'll get to the Euro model more in a bit, but for the sake of starting with what could happen, I'm going to go to the last two GFS runs.
Today's early morning run signified that the first in the series would be a fairly weak clipper system which would be in and out by Tuesday. This feature was also present in the midday run, so the model seems to be convinced that it's going to show up. I wouldn't expect this system to produce more than a dusting in the northern areas of the lower peninsula and if predicted temperatures are to be believed, we could just be looking at rain or flurries with little to no accumulation. The next portion would show up Wednesday. Both runs of the model also suggest this would be pretty much pure rain.
Thursday is when it starts getting really tricky.
The morning run has temperatures start to drop at all levels. Another system is forecast to come through on this day. This would mean snow for the north, and a lot of it - 9 inches or more. It would also mean potential sleet or freezing rain for Mid-Michigan. The afternoon run predicts the storm to have a more northernly track, dumping snow across the U.P. and rain pretty much everywhere else. A thin line of freezing rain wouldn't be out of the question across the extreme northern lower peninsula if this forecast were to verify.
Friday is where it starts getting potentially ugly.
The morning run differs quite a bit from the afternoon run, and is my preference if you ask me. The fourth and final surface low in the series would be a Nor'hook type storm, the surface of which would crawl up the "sweet spot" in Ontario to bring Mid Michigan a lot of snow. Like the day before, this would be an 8-10 inch event, meaning the northern two thirds of the lower peninsula would be seeing similar amounts of snow on the ground by the time everything was said and done. The afternoon run, however, is flat out scary-looking.
It has a more positively-tilted low taking a similar track, but in this case a fairly ugly looking "mixing" region exists. The reason for different types of precipitation is because of changes in temperature at different levels of the atmosphere. For this scenario, at the 850mb "mid-level", you have temperatures that are forecast to be quite warm:
At the level immediately below it, the 925mb level, you start to see temperatures drop below freezing:
Finally, at the surface, you also have temperatures below freezing in a lot of places:
This is the mixing region, and it's the type of scenario is the primary ingredient for either sleet or freezing rain. Depending on how cold the 925mb temperatures get - namely, if they're below freezing - you could see sleet. Otherwise, if temperatures at the surface are below freezing, you see what in my opinion is the nastiest type of winter precipitation: freezing rain. There would be a LOT of it here, too - the moisture content depicted would still be enough for nine inches of snow at a 10:1 ratio, so we're talking a potential major ice storm for at least a few hours should it stick.
Now that all the doom and gloom is out of the way, let's move on to the good news. Both runs of the aforementioned models predict temperatures to rise considerably by late Saturday/early Sunday, meaning any ice/snow accumulation would quickly begin to melt. We're talking 40s and 50s, so even if one of these forecasts verified, it'd be gone in a hurry. The second part of the good news is that the European model predicts the absolute inverse of this forecast, and if you ask me it makes a little more sense.
The Euro model has the temperatures in the week start off cold, with some snow on Tuesday and Wednesday from the weak clipper systems. By Friday morning, however, things really start to heat up:
This as a cold front/surface low moves in from the west, which would make for some impressive thunderstorms down south and plenty of rain up here.
This is the more likely scenario if you ask me, because most often when clippers descend they bring cold air with them, and when storms come up from the south they bring warm air with them. This has everything to do with the track of the Friday storm, though. The Euro model has it tracking up through the plains, with Michigan in the neutral-to-warm sector. The GFS is predicting it to go up through the Ohio Valley and put us in the neutral-to-cold sector. This will be the single biggest deciding factor in what form of precipitation we see. I tend to trust the Euro a bit more this far out with storm track, and it's world's apart from the GFS in that regard.
To summarize:
• A series of storms should affect most of the state next week, bringing potential rain/light snow to different areas early to midweek, and potentially heavy snow or freezing rain by late next week.
• Confidence is very low at this time, as the model divergence is large even among consecutive runs of the same model
• I have a distinct impression this will be an "all or nothing" event, with very little room for a middle ground - by next Monday we should have a much clearer picture of what's going to happen
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