DETROIT – The National Weather Service has issued a winter storm warning for Genesee, Lapeer, Livingston, Macomb, Oakland, Sanilac, St. Clair and Washtenaw counties until 11 a.m. Thursday.
I'll be very honest about this: the weather scenario that will play out tomorrow is so complicated that it's even hard to write about. This is not only because there are still some very important differences among the computer models (which means significant ramifications on what type of weather we get, and how much), but also because of the changes in precipitation type that will occur. I'll do my best to explain this to help you plan, but keep in mind that there still could be some changes.
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Alright, let's get started:
Clouds will increase tonight, with some rain (and possibly some snow) developing close to the morning rush. Lows will drop to around 30° (-1° Celsius for our Canadian friends), then rise near or above freezing by the time you head off to work. Northeast wind at 8 to 13 mph. Here's our RPM model's projection for 7:00 AM. Remember that greens, yellows and oranges are rain, the shades of blue are snow, and purple is the transition zone between the rain and snow.
As we move through the day Wednesday, a line will set-up...southeast of which will be mostly rain, and northwest of which will be mostly snow. Where that line materializes is the most critical part of this forecast. This is the RPM's depiction for 3:00 PM Wednesday afternoon. Note that the rain / snow line runs from north of Port Huron to roughly Jackson. At least that's what the RPM says. Some other models (most notably the NAM and ECMWF) offer a more eastward, colder solution.
Temperatures Wednesday should reach the upper 30s (4° Celsius). It's also going to become quite windy as the storm system approaches.
Notice how the rain / snow line hasn't moved much through early Wednesday evening. That's why I've been telling you that, even though the exact placement of the rain/snow line is still not certain, those of you who stay all snow will get much more snow accumulation that those who get some rain. Mother Nature has only one bucket of moisture to dump on us, and if some of that falls as rain, that cuts down on what's left to fall as snow.
Big changes occur between 8:00 PM and midnight. As the area of low pressure starts pulling off to the northeast, colder air starts pushing eastward which, accordingly, pushes the rain / snow line to the east. By midnight or 1:00 AM, all of us should have changed to snow, and it'll really be coming down for a while. Needless to say, the Thursday morning rush hour is going to be a mess, and there will probably be a lot of school closings on Thursday as well.
It'll still be snowing a good part of Thursday, although the snow intensity should gradually wane. Wind will still be blowing strong, so blowing and drifting is a concern. Also remember that there could be ice under the snow...especially in areas that get rain changing to snow, or snow that initially melts on the warmer pavement before accumulating.
Everybody is asking about how much snow we'll get. I almost hesitated even posting a graphic with this information, because there can be such a radical change in these amounts depending upon where that rain / snow line sets up. So I'll show you what the RPM is projecting, but with this caveat: consider these number preliminary and subject to adjustments.
Areas that get mostly rain on Wednesday will probably accumulate around 3-5" of snow after the changeover. Areas that get all snow will probably accumulate 6-9" of snow. The toughest part of the forecast is for those of you who get both rain and snow on Wednesday (if the rain / snow line moves during the day).
It's tough to nail down a snow total, but somewhere in the 4-7" range is probably prudent. And keep in mind that at least the first half of this snowfall will be a wet, heavy snow that is tough to move (and drive through). If you are elderly, not in good health, or have heart or respiratory problems, DO NOT SHOVEL THIS SNOW.
One final note about the snow totals: due to our warm winter, Lake Huron is wide open, with very little ice -- so lake effect comes into play. This means that the northeast wind associated with the storm will significantly enhance the snow in the Thumb -- some areas could exceed a foot of snow (even though the RPM doesn't seem to be picking up on this).
Well, that's my latest thinking on the storm. This is a tough one, folks. Remember to follow my updates on Twitter for periodic updates.