Every spring, summer and early fall, trade winds pick up about 882 million tons (800 metric tons) of desert dust from North Africa and blow it west across the Atlantic Ocean. This year, NASA-NOAA’s Suomi NPP satellite first observed the huge plume of Saharan dust streaming over the North Atlantic starting on June 13. Since then it’s traveled all the way to southern coast of the U.S.
While the dust can affect air quality and isn’t healthy to breathe it has side benefits including fertilizing soils in the Amazon and building beaches in the Caribbean. The dry, warm wind blowing from Africa also can suppress the formation of tropical storms that might evolve into hurricanes. The dust will also make for a colorful red or orange sun around sunset. Called the Saharan Air Layer (SAL) the dust reaches from 5,000 to 20,000 feet high (1.5-6 km) in the atmosphere.
Observers across southern Louisiana, Mississippi and northern Florida may notice hazy, white skies from the arriving plume today. The sun should also appear orange or red well before sunset. Where the dust is thick enough you may see the sun fade and disappear in a brown-red haze even before it sets. NOAA meteorologists expect the cloud to advance over the central U.S. including southern Illinois, Kansas and part of Ohio by the weekend.
Watch the weather, and if your sky looks like frosted glass when it was recently blue, chances are you’ve got a blast of Africa overhead. Although dusty sunsets look distinctly orange the overall scene is monochromatic compared to a clear, clean sky. Deep blue turns pale white during the bright daytime hours and then a murky, brownish-yellow by early evening. At night under a cloudless sky the stars will be noticeably fainter while the moon will shine like a tangerine.
Dust storms on Earth eventually run their course, but on Mars, a planet that’s basically one vast desert, they can last much longer when favorable atmospheric conditions prevail. Multiple small storms occasionally merge into a planet-encircling monster storm like what happened in 2018 during Mars’s last close approach to Earth.