Beefy rain Sunday into Monday seems to be like an early chance of flash flooding

More widespread rain and thunderstorms are expected to fall across all of Michigan Sunday into Monday. Northern Michigan received several inches of rain this week, highlighting it as a potential flash flood area.

While most of us should get some more useful rain Sunday night and Monday, the weather system has the potential to produce streaks of three to four inches of rain. Flash flooding is possible in northern Michigan. Southern Michigan was very dry going into this week’s rain, and soils in southern Michigan can still take several inches of rain before flash flooding.

Source: National Weather Service – Gaylord, MI

I see four components lining up to make four inches of rain total by Monday night.

First, we will have very abundant water vapor in the air over Michigan. It is these tiny invisible droplets that eventually stick together to form raindrops. Imagine a sponge full of water but not flowing. As you squeeze the sponge, empty the water out of it. We will have a sponge loaded in the air.

Then, a cold front will move almost due south over Lower Michigan. This motion is important because that type of movement tends to have a slower speed of movement compared to a cold front that moves west to east across Michigan. A slower speed means the thunderstorms can last longer.

Third is the possibility of “echoes of a train.” Train echoes are individual thunderstorm cells that move west to east over the same location, like train cars traveling over the same tracks. In the case of a train echo you can get three or four half hours of thunderstorms at the same point. When each thunderstorm drops an inch and a half to an inch of rain, four bursts of that size really add up.

Finally we will look at the time of day for the storms. This is very important. Peak heating in the late afternoon and evening makes for the strongest thunderstorms at that time of day. There is also a secondary instability peak an hour either side of sunrise.

So we are likely to see a train of thunderstorms moving east, and gradually shifting south. Storms will be strongest in the early morning and late afternoon / evening and then weaken in the late morning and early afternoon. This whole situation will go from Saturday night in the UP to Monday night in southern Lower Michigan.

Here is a rainfall forecast showing six hour periods of rainfall totals.

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Six hour rain forecasts from Saturday night to Tuesday morning.

Here is a full rain forecast. You can expect the heaviest thunderstorms to drop two to three times the general rainfall forecast.

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Total rainfall forecast through Tuesday from NOAA’s Weather Prediction Center

In general you can see that we can all expect another nice rain, and that should relieve any dryness in the soil for our landscapes and farmers’ crops.

The National Weather Service states that two to three inches of rain could produce flash flooding in the UP and northern Lower Michigan, where up to three inches of rain fell earlier this week. Watch for updates as the weather system moves closer to Michigan.

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