Tuesday, April 29, 2014

This rain won't clean your car off!

We've received several reports from social media this morning of sprinkles on cars and other outdoor objects that leave behind a residue, or dust, after evaporating. In fact, I had noticed the same thing on my windshield yesterday and assumed pollen, but didn't look closely. The pictures received though we definitely NOT pollen. It was dirt.

Morning sprinkles evaporated, leaving these dust spots on Carissa H.'s car (@rissa424)
A couple of thoughts immediately came to mind. First (and this one seemed less plausible than the second) was dust/dirt from Arkansas that was sucked up by tornadoes on Sunday and deposited downstream. I had heard of such a thing happening, but the timing (2 days later) and wind patterns didn't quite make sense. The second option was dust from the plains carried east on upper level winds. Knowing there was a massive trough over the middle of the country and a strong jet stream blowing from west to east across our area, I knew that option was more plausible.

Sure enough, after a little digging and checking in with the NWS to get their opinion, I'm fairly confident that it is indeed dust from the plains. For the past few days, strong and gusty north wind has prompted dust storms across the central and southern plains. In fact, the NWS watch/warning map below shows Wind Advisories and High Wind/Dust Storm Warnings in effect right now across the plains.

Then, I got a text from a family member who happens to be on the interstate in the TX panhandle describing vicious wind and "raining mud!" Sure enough, dust storms were in progress and light rain was dropping the dirt back to earth! Dust storms are known to eject fine dust particles thousands of feet into the air where they are carried by the currents downstream.  Below is the current upper level (about 35,000') jet stream courtesy of an awesome animated web tool called the "Wind Map."  The large L is the low pressure trough that the jetstream wind is flowing around. Key points are labelled.

So you can see that as the dust is picked up and ejected into the upper levels of the atmosphere, it gets carried downstream and deposited or rained out of the atmosphere! The light rain falling this afternoon is not going to be good at washing pollen off your car, but instead could result in a trip to the car wash thanks to strong wind and plains dust that is transported all the way to Tennessee!

Erik Proseus
MWN Meteorologist

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1 comment:

Anonymous said...

Thanks for this info. We were discussing at the salon this afternoon the dirty rain on all our cars!!!