Tracking our first measurable snow of the season

By Stone Andrews Last updated Nov 12, 2021

The weather pattern until Saturday will be characterized by isolated, very light rain or snow showers. But what comes in on Sunday is not dissipated and may not be easy. I’ll dive into these details in a moment.

But first, if you have plans for Friday afternoon or evening, there will be a few light showers, and any heavy rain will have sleet too (I’ve already seen a video of sleet falling in Howell). I think the activity will decrease overnight, although some light showers of snow may form later in the night. Lows in the lower to mid 30’s (0 to 1 degrees Celsius), with a southwest wind at 10 to 25 miles per hour.

The sunset is at 5:14 p.m. tonight and the Saturday morning sunrise is at 7:22 a.m.

Saturday

Occasional light snow showers in the morning and light rain showers in the afternoon will pervade the area on Saturday. It will also be airy, which adds to the cold of the day. Temperatures should scratch their way into the low to mid 40s (6 degrees Celsius) in the early afternoon with a westerly wind traveling at 10 to 20 miles per hour.

There may be a partial clearing on Saturday night, but the clouds will increase on Saturday night and there may be light showers of snow or snow later in the night (I think we will be dry for our Saturday night plans). Lows in the lower to mid 30s (0 to 1 degrees Celsius).

Sunday snow – what we’re chasing

The upper level disturbance I discussed yesterday has just moved away from the Pacific Ocean and crossed the Pacific Northwest coast and is now available for inspection by our land based overhead balloon network (these balloons are called radiosondes, just in case you’re wondering) . . Hence, our computer models are developing a better way of handling this system.

This fault will create a surface depression that will move from Montana to southern Minnesota on Saturday evening and then to near Chicago by Sunday morning. At that point it will turn east and be pretty close to the Michigan-Indiana-Ohio state line.

The key to determining the amount of snow on Sunday is twofold: the thermal structure of the lower atmosphere and the temperature of the road surface.

Let’s address the lower atmospheric temperature first. Three computer models (IBM GRAF, NAM, and GFS) this afternoon suggest it will be cold enough to produce wet snowflakes, with a sufficiently shallow layer of freezing temperatures close to the surface that the flakes don’t have time to melt and transform to give raindrops. One model (ECMWF) suggests that we will see a mixture of precipitation. At this point, especially since GRAF and NAM are high resolution models that match, I’m relying on a mostly snow scenario (maybe some rain could get in the way in the far south).

The next consideration is the road temperature and right now the road surface is above freezing.

So I expect the snow to increase on Sunday and possibly even moderate at times. It starts to accumulate on grassy areas as well as on raised areas (picnic tables, garden furniture, grills, mailboxes, etc.) as these are not insulated by the warmer ground below and cool down to freezing point due to the snow.

However, it takes longer to cool to freezing. Eventually, and especially when the snow gets moderate, it will, and we’ll see some slush develop on the sidewalk.

All in all, I think we’ll see maybe an inch or two on grassy and raised surfaces, but less so near Lake Erie, St. Clair, and Huron as it’s a little warmer there. Of course, if the ECMWF model is the one that verifies this and we have a rainfall mix at the end, the amounts of snow will be less.

Conversely, higher elevation areas, like the elevated terrain in northwest Oakland County, might see a little more.

** I will have a new high resolution computer model tonight … I think I have enough of it to have a full update that you can show up on Local 4 News at 11 then. **