Many Central Texans woke up Thursday morning to a delightful sight: a light covering of snow on roofs and cars. But after it melted, what was left was decidedly less delightful: a layer of grime on the car.

This morning, Steve Marsh asked us on Twitter: Why?

@KUT why are all the cars dirty in Austin after the snow melted? #dirtysnow — steve marsh (@the_steve_marsh) February 7, 2020

We, too, were curious. So we called the National Weather Service to find out.

"Precipitation ... rainfall or snow ... forms from something that we call cloud condensation nuclei," Brett Williams, a meteorologist at the NWS in New Braunfels, told KUT's Nathan Bernier. "Typically, little pieces of dust or other particulates, which the water droplets will coalesce and form around."

In other words, water condenses around little bits of stuff in the air and — in the case of snow — freezes and falls to the ground.

Williams said the snowflakes in our "storm" the other night likely formed around dust blowing in from northern Mexico and West Texas.

"So, what happened was when the snow fell and eventually ended up melting and evaporating, it left the dust behind ... on cars and surfaces."

Williams said this doesn't just happen with snow. He recalled a rain event a few years ago that left a fine coating of dust behind, too.