Why the rain in Beryl is not the usual Michigan rain

You may think rain is rain. That’s not entirely true, and the remnants of Hurricane Beryl will show you the difference.

Tropical rain like the heavy rain we have tonight and Wednesday comes from a different part of the globe than most other rainfall in Michigan. The rain now contains some moisture from Africa, the Atlantic Ocean, the Gulf of Mexico, and the southern U.S. states. The majority of our rain contains moisture from the air over the Pacific or the western and central United States.

The first difference in tropical rains is the size and density of the raindrops. Tropical rains, believe it or not, have smaller drops with more drops in a given area. This means that the heavy tropical rain actually shows up on radar as much lighter rain than is actually falling. Any given national weather service office can switch the radar to a “tropical mode” which will then give a more accurate representation of very heavy rain. When we have a normal non-tropical thunderstorm, the heavy rain will show up on radar with the high end of the color scale. The colors can be the last shades of purple and even white, indicating extremely heavy rain. The same rain intensity from a tropical system would show up as yellow if our Michigan radars were in normal mode. Yellow on a radar means a moderate, steady rain.

The National Weather Service in Grand Rapids actually told us meteorologists that they have switched Grand Rapids’ radar to tropical mode.

Here you can clearly see how the radar image differs from a radar in tropical mode to one without tropical mode. The radar in White Lake, MI, shows the rain less clearly. It has not yet been switched to tropical mode.

While admittedly closer to some of the heavier rain in northern Indiana, the Grand Rapids radar shows the rain significantly more than the Detroit area radar. Keep in mind that the Grand Rapids radar is in tropical mode.

For the next difference, you don’t need a technical instrument like a radar. All you need is the best weather observation tool there is – your eyes. The clouds will look different. The tropical clouds usually have a lower base, sometimes as low as 300 to 600 meters above the ground. You may feel like you can touch the clouds. Our normal rains would have a low base of 1,500 meters and many bases are higher than 1,500 meters.

The color of the sky can vary. I have noticed a slight greenish tint at times. Why? I don’t know, but it is probably due to the different cloud condensation nuclei in a storm that has moved from Africa across the Atlantic, through the Gulf of Mexico and from Texas to us.

Now think of the different things that can be contained in a raindrop from Africa and the tropics. I haven’t seen any real research on this, but tropical rains can contain more and different nutrients in a drop. I call this rain “the great greening.” Look at your lawn. Look at your vegetable and flower garden after the rain. If it isn’t flooded, your garden will have a lot of growth this week. It will look like you fertilized it. It will soon get nature’s “miracle growth.”

Rain from other parts of the world also has its downsides. These rains and the muggy air can bring with them plant diseases that are not normally found in our area. Plants also have immune systems. They may not know how to fight off a particular airborne plant pathogen. You probably won’t notice this, but growers of cucumbers, tomatoes and sugar beets might.

The last thing we’ll notice is the post-storm sweat box we’ll be in. The air won’t be replaced by cooler, drier Canadian air like after a typical cold front. Instead, there will be a lot of evaporation of standing water. From Thursday through the weekend, humidity should be very high – a real tropical feel in the air. Get ready for two showers a day.

Keep your eyes peeled on Wednesday as the heart of the storm moves through our state. It will be a different kind of rain.

RELATED LITERATURE: Heavy rain up to 6 inches possible. See where in Michigan the beryl rains will be heaviest