"Dirty Rain" reported across Miami Valley Wednesday

Credit: DaytonDailyNews

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Meteorologist Carrieann Marit explains the 'dirty rain' that fell in the Miami Valley.

Credit: DaytonDailyNews

Did you happen to notice that your car looked like it had been sprayed with muddy water Wednesday after rain showers moved through the area?

Many of you sent me messages about what appeared to be "dirty rain". It turns out, that was exactly right! The rain was dirty - but why?

On Tuesday evening, we had a warm front move across the Miami Valley that caused winds to shift from the west to south / southeast Tuesday night. This shift in wind direction likely was somewhat responsible for allowing higher concentrations of dust/dirt to advance into our area Tuesday night before showers arrived on Wednesday.

Once the showers pushed into the area, the water/rain mixed with the dust/dirt particles making for a somewhat muddy rain.

Now exactly where the dust/dirt actually came from is unclear. It could have been some smoke from farmers or others clearing fields after a couple of nice mild days However, a review of high-resolution satellite imagery which can many times detect and see smoke revealed nothing significant.

There may have been some other airborne pollution that was transported from a factory or plant. However, the fact that the "dirty rain" was noticed in more widespread areas across the Miami Valley would suggest it would have had to have occurred by a larger source.

Most likely, the dust/dirt was just lofted into the air by gusty winds blowing across vegetation-free farmland to our south. It is possible even some ash, which can be very light compared to dirt, was also picked up by gusty winds from recent fires earlier in the fall and early winter across the Appalachian Mountains.

Whatever the source, it is not uncommon for rain to be somewhat dirty, especially if it is very light and brief. The rain does do a good job of cleaning the air of dirt, dust and pollen if it is heavy enough, but when the rain is light and brief, the dust that mixes with the initial raindrops can deposit on your car and other surfaces as the water evaporates.

It is important to note, that raindrops actually require condensation nuclei, such as dust particles, to even form. So the dust is not necessarily a bad thing. But that would all depend on the source of the dust, of course.

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