Still looking good for the Tuesday/Wednesday storm

We are only 84 hours out from what I believe will be the most significant snow event we have seen thus far for this winter. The overall long-term pattern still doesn't favor our area, but luckily enough, a very strong upper level low will drop south and phase with another system, resulting in what will likely be a nice snow event for our area.

Last night, I mentioned that current model trends place SE Michigan in the dryslot with the storm, which would cut down on accumulations. Now, the models have trended towards placing SE Michigan in the deformation zone of the storm, which would result in a prolonged period of heavier snow, with higher accumulations the result. The 12z GFS (top image) and 12z NAM (bottom image) illustrate this nicely.


There is now a strong agreement among four of the major models (GFS, NAM, ECMWF, GGEM) that SE Michigan will not get dryslotted with this storm. Obviously, this could change, but right now the trends are favoring us.

So, let's talk about how this storm should play out for us, and what it means w/ regards to a snow day. Since last night, trends have been to slow down this meat of this storm just a bit. Snow should still start around noon on Tuesday, but the heaviest snow is now expected to fall early on Wednesday morning, which is perfect timing. The storm will likely wind down around or shortly after noon Wednesday. Obviously, the timing is good for a snow day, but what about the amount of snow that is going to fall?

Happily, I can say that the amount of snow that is going to fall will also likely be enough for a snow day. The GFS and ECMWF have been consistent in giving us a good amount of precipitation with this storm, and the GGEM, while not as wet as the GFS or ECMWF yet, has been trending in our favor. The NAM is currently the driest of the models, but I think even it would give us enough precipitation for 4+" of snow. And considering the strength of the upper level low that will be moving just to our south, I tend to think the NAM is slightly underplaying the amount of precipitation we will receive from this storm.

A couple of other factors should also make this system a good snow producer. As I mentioned earlier, the models have trended towards putting SE Michigan under the heaviest band of snowfall with this system, known as the deformation zone. The track of the upper level low shown by the GFS, NAM, and ECMWF (through Central Illinois, Indiana, and Ohio) is just about perfect to put SE Michigan in the heaviest band of snowfall.

Also, as I mentioned last night, the snowfall ratios with this system will likely be higher than normal. What do snowfall ratios do w/ regards to accumulations? Here's what I posted last night...

"As a basic example [this won't necessarily be exactly what happens with this storm], if we got .5" of water falling with 10:1 ratios, that would result in 5" of snow. With 20:1 ratios, .5" of water would result in 10" of snow."

Anyways, with the strong upper level low pulling down cold arctic air, we should have no problem achieving 15:1 ratios with this event, and they could be even higher, although I will currently forecast assuming a 15:1 snow ratio.

All these things are shaping up to give us a good chance at a snow day on Wednesday. I currently expect this storm to give us anywhere from 5-11" of snow (I will whittle down this range of accumulations as we get closer to the storm). This storm will have a favorable timing, with the heaviest snow likely falling between midnight and 6 a.m. Wednesday, leaving the road commission little time to clear it out of the way. Not only that, but I expect powdery snow and high winds to blow the snow around, likely resulting in drifts of over 1'. Also, snow will likely still be falling during the morning commute Wednesday.

Combine all of the above with the fact that it's February, and we haven't had a snow day yet, and I am willing to raise the snow day grade to a B (good chance of a snow day, but not a lock) for Wednesday. Watching this storm unfold over the next few days should be very fun...