All data continues to show a rapid change in the weather across Michigan late this week. Between Wednesday and Saturday, our weather is going to gradually become very wintry.
The cold air should set the stage for accumulating lake effect snow by Friday and Saturday.
Lake effect snow needs a few conditions to come together for snow to be heavy.
First we have to have enough temperature difference between the air near the surface of the Great Lakes and 5,000 feet up. If all other conditions for lake effect are in place, lake effect will start at a ground air temperature to 5,000 foot temperature difference of 25 degrees F. As the temperature difference gets larger, the possibility of heavy bursts of snow increases.
By Saturday morning I’m calculating a temperature difference of 45 degrees F, just 10 degrees less than the heavy snow level. So there is plenty of cold air over 50 degree Lake Michigan water to generate lake effect snow.
The second big factor is wind direction. An important part of this wind direction factor is how long the wind stays blowing from the same direction. Early season cold air often has shifting wind directions going from southwest to west to northwest. As the wind shifts, lake effect snow shifts locations also. Shifting bands of snow limit the snow totals, but also spread lighter accumulating snow across a larger area of the snowbelts. I think we will have shifting bands of lake effect snow with this first lake effect situation.
Of course wind direction is important for what locations get lake effect. The forecast above for Saturday shows the classic northwest wind. The northwest wind will generate lake effect in the typical snowbelt regions of the U.P., northwest Lower Michigan and southwest Lower Michigan.
But remember that shifting wind direction will make for a more off and on type snow. Also, I’ve found the warm air over the water will keep the surface winds more southwesterly for a day or two of the first real cold.
That’s why it will likely take until Saturday before the lake effect is fully developed.
So now I have to show you a snowfall accumulation map, right? Right.
Now don’t focus on exact amounts right now. Focus on where the accumulating snow is expected. All three snowbelt regions on Michigan should get in on some lake effect snow. This forecast is through midday Saturday. There will be more snow into Sunday. Accumulations have to factor in warm ground melting the snow as it falls. I’d say large areas of two to four inches of snow are a good place to start.
The view of west Michigan and northern Michigan is going to change quickly between Wednesday and Saturday.
It will be cold enough with vigorous enough lake effect to bring spurts of snow to eastern Lower Michigan also. This should include the big cities of southeast Lower, like Detroit, Ann Arbor and Jackson.
Unfortunately if you need dry weather and mild temperatures to accomplish an outdoor project, you probably only have part of Monday, November 5 in your favor.
Get ready for a big weather change in Michigan late this week.