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Boston Globe

Rare ‘dirty rain' traced to desert dust 1,600 miles away gets swept up in New England storm

The dirty rain in Maine came from desert dust that had hitched a ride on strong winds out west, more than 1,600 miles away. 'It's kind of cool to think it was transported hundreds of miles across the country' to the Northeast, said Christian Bridges, a meteorologist at WGME-TV in Maine. 'This phenomenon has been seen in the Midwest many times during big storms when dust from the Southwest gets caught up in storm systems, especially in the winter. It's more unusual that the dust made it all the way to New England.' Anybody else notice that the rain we got Friday night/Saturday was full of dust and dirt? All the cars are caked in it! — Christian Bridges 🌩️ (@ChristianWGME) Advertisement Using NOAA's Hysplit model, which simulates the paths of air parcels, meteorologist Trey Fulbright traced the cloud of dust to the Southwestern United States. 'I used a backwards trajectory to see where the air parcels came from,' said Fulbright, a meteorologist at KDKA-TV in Pittsburgh, Pa. Satellite images show that powerful winds kicked up the dust across parts of New Mexico and west Texas on April 17. At the time, winds were gusting to 65 miles per hour in Roswell, New Mexico. The dust was swept up to an altitude of about 10,000 feet, below the level of rain clouds, as it was carried off. Advertisement A satellite image showing the dust cloud moving from the West. NOAA The trajectory of the dust cloud as created from NOAA's Hysplit model. Trey Fulbright These tiny particles, while managing to travel hundreds of miles, 'moved quickly. Dust that left the Southwest the evening of April 17 made it to Portland by the 19th. That's less than two days,' Fulbright said. So when the precipitation fell over portions of Maine on April 19, 'the rain kind of grabbed the dust as it was falling and brought it down to the ground,' Bridges said. It's a reminder that what happens in one part of the country can quite literally land on another — car hoods and all. 'On that night of April 18 into the 19th, the rain was fairly light, so that allowed the dirt to get stuck to cars and other surfaces and not get washed away,' said Bridges. To survive such a transcontinental journey, scientists said, the particles need to be small enough to fight the forces of gravity so they stay suspended in the air. 'Smaller particles — less than about 2 microns — can stay aloft in the atmosphere for a week to 10 days, sometimes longer, before settling,' explained Joel Thornton, an atmospheric science professor at the University of Washington. To put that into perspective, 2 microns is about 1/50th the width of a strand of human hair and so small that a single red blood cell is about four times larger. These tiny particles become cloud droplets, but even then, they are too light to overcome rising air. 'Cloud condensation nuclei are usually the smaller particles because they're more numerous. One droplet forms on each nuclei, but it takes many merging to create a raindrop big enough to fall,' Thornton said. Advertisement Chris Gloninger is a meteorologist and a senior climate scientist at the Woods Hole Group.