Enhanced Alberta Clipper will dump snow on Southeast Michigan this weekend.

A low pressure system will drop out of Alberta tomorrow, then dive down to around St. Louis by tomorrow night. From there I expect this low pressure system to track approximately from St. Louis to Normal, Illinois to Toledo, Ohio and then off to the northeast into Canada. This low pressure system will likely produce a nice snowstorm for Southeast Michigan this weekend.

Now, Alberta Clippers usually give us only "nuisiance snowfalls" of around 3-6". Earlier this week, that was what this clipper was supposed to do, as it was originally forecasted to track well to our south (from Lincoln, Illinois to Indianapolis to Columbus). However, forecast models have moved the track to the north in the last day or so, and are now in strong agreement on a track similar to the one I mentioned in the first paragraph. This track will allow Southeast Michigan to get in on the main snow shield, and therefore get the highest accumulations out of this system. And since this is a stronger than normal Alberta Clipper, snow totals will be higher than the normal 3-6" expected from Alberta Clippers.

How high will snow totals be? Here's my snowfall map:


My accumulations are on the high end of the forecasts of professional meteorologists, and here's why:

First of all, some definitions will be necessary...

The GFS and the NAM are the two forecast models which I use to figure out approximately how much precipitation we will receive from a particular system.

QPF is an acronym for "Quantitative Precipitation Forecast". It's basically a fancy way of saying how much liquid precipitation will fall in a particular area based on forecast model guidance.

Finally, snow ratios are how many inches of snow you could receive from one inch of rain. For example, a 10:1 snow ratio (a normal snow ratio at 32 degrees) means that for every inch of rain that falls, you would get 10 inches of snow. Since we will have temperatures in the mid 20's on Saturday, we will get higher snow ratios (around 15:1 to 18:1). Multiply the QPF and the expected snow ratios to get the expected snowfall.

So, here goes nothing:

A blend of GFS and NAM QPF totals generally supports 0.30-0.55” of QPF falling in SE Michigan with this system, with the higher QPF over the southern portion of the forecast area, closer to the low pressure system. Assume 0.45-0.55” of QPF over the southern half of the forecast area, with snow ratios between 15:1 and 18:1. 0.45*15 = 6” of snow (lower limit) and 0.55*18 = 9.9” of snow (upper limit). Therefore, I have forecasted a general 6-10” of accumulation over the southern half of the forecast area. Then, assume 0.30-0.45” of QPF over the northern half of the forecast area, with snow ratios between 18:1 and 20:1. 0.30*18 = 5.4” of snow, and 0.45*20 = 9” of snow. However, I have bumped down accumulations about an inch for the northern half of the forecast area because clippers tend to have fairly sharp accumulation cutoffs.

I have also included a "locally 12 inches" mention over the southern half of the forecast area because a heavier band of snow (called a deformation band) will set up somewhere to the north of the low pressure system. Areas in this band will likely receive a foot of snow. The favored area for this band of snow will probably be somewhere between I-69 and I-94 (that's right, our area!).

So, what does this all mean for snow days? This would be a lock if this storm was occurring during the week, but unfortunately for us, the brunt of the snow will fall on Saturday. I would expect the snow to start Saturday morning, with the heaviest snow falling between noon and 4 p.m. Saturday afternoon. All snow will taper off by early Sunday Morning. However, all hope is not lost. First of all, you can't discount the fact that we have a road commission that is slow at best at clearing the roads. So, some back roads may still not be cleared off by Monday morning, which could result in a snow day.

Another nice possibility is that some model runs have shown that this system could stall out a little bit on Sunday morning because of a high pressure system in the Atlantic Ocean. If this happen, we could end up with even higher snow totals than currently expected and snowfall ending later than expected (late Sunday morning), which would likely mean a snow day for us on Monday. This could possibly be the reason why the National Weather Service in Detroit has bumped our forecasted snow totals up from 6-9" this afternoon to 7-13" currently.

All in all, this is an extremely promising storm system, and our best hope for a snow day in a while, despite the horrible timing.