Crop Comments: Another SAL this summer?

The Saharan air layer (SAL), often called Saharan dust, consists of sand, dirt and other dust lifted into the atmosphere from North Africa’s vast desert. This dust is carried in the African (atmospheric) waves, which push westward into the Atlantic Ocean. SAL is a well-mixed dry pocket of air usually hanging out between 5,000 and 15,000 feet above sea level. Since one of the key ingredients for tropical cyclone development is a generous influx of moisture, Saharan dust often inhibits tropical development.

Once a pocket of Saharan dust moves westward over the Atlantic, it’s relatively easy to track using infrared satellite tools. This model combines forecasted movement of the SAL with the Global Forecast System (GFS) precipitation rate and pressure contours to depict movement of the layer. It’s fairly easy to track a SAL movement toward the western hemisphere.

Mysterious as SAL may be to some, “it’s just dust,” according to Alex DaSilva, Accuweather’s lead hurricane forecaster. “It won’t hurt you. Saharan dust is just dust and sand from Africa, transported via wind around this time of year.” June and July are the months with most such dust.

Saharan dust can influence how storms form in the tropics. DaSilva said that a warm, moist environment is crucial for creating storms. The dust acts like silica packets found in packaging, sucking out any moisture that might be in the atmosphere. “Dust basically chokes off these systems, because they demand plenty of moisture and when you’re taking away that moisture, it makes it harder for thunderstorms to develop,” he said.

Coincidentally, such dust appears during a period when hurricane season is (normally) calmest. (A glaring exception to that statement manifested itself as Hurricane Beryl, which formed in June 2024, waxing into the earliest Category 5 hurricane ever recorded in the Atlantic, according to the NOAA.)

Two terms, conspicuous by their absence in DaSilva’s discussion, were “SAL” and “fertilizer.” I first learned about SAL over five years ago, when one version of it blanketed much of Europe, including the part of Switzerland, where my son’s family resides. They sent me pictures of an orange Swiss sky, pigmented by fine, light orange, airborne sand. The sand blew its way from the Sahara across the Mediterranean.

On Feb. 8, 2021, BBC journalist Steve Brown wrote, “Skies became orange in certain parts of Europe after winds carrying Saharan sands swept through. Though the phenomenon happens every year, regional meteorologists said the winds were stronger that time, with a greater volume of sand particles in the air.”

Brown explained that commonly strong southerly winds carry dust from the vast African desert during winter. But this time, such a climate event occurred unusually intensely, and these dust clouds changed central Spain’s ski slopes from white to dark tan. Such discolored snow made skiers rewax skis prematurely.

Now for fertilizer, as it materializes as a blessing accompanying Saharan fallout. Part of the U.S. got such a dose several months before Switzerland got dusted. In late June 2020, a Saharan dust plume reached North Carolina and Virginia. Skies were occasionally hazy then; airborne dust particles irritated eyes and respiratory systems, according to the National Weather Service.

The good news came in the form of the SAL – although few crop growers know about this fertility source. The boundary between the SAL and low-level moist air, where the trade winds blow, is what climatologists call the trade wind inversion. This is a region of the atmosphere where air temperatures increase with altitude. (Normally, atmospheric temperatures decrease with altitude.) This inversion effectively puts brakes on thunderstorms growing vertically. This braking occurs because air in thunderstorms’ updrafts encounters zones in which uplifted air is cooler, thus less buoyant than surrounding air. When the SAL-borne cloud takes a northwesterly turn after departing Africa, it shades the southern regions of the North Atlantic.

These dust shadows lessen solar radiation hitting the ocean surface, reducing sea water warming and robbing the energy required to form hurricanes. If this steady, roughly 3,000-mile-long dust cloud maintains its heading (now west by southwest), it ends up in Brazil’s Amazon Basin. Sometimes this dusty plume deviates far enough north to coat parts of the southeastern U.S. with “African fines.” It feeds Brazilian rainforests (often called “the lungs of our planet”), just enough to replace many nutrients lost there. Scientists thus are able to determine how much phosphorus gets wafted from one of Earth’s most desolate places to one of its most fertile.

Phosphorus updrafted from Saharan sands originated from that desert’s history as a lakebed. Quoting scientists from NASA’s Goddard Space Center, “This transcontinental journey of dust is important, because the dust’s cargo, picked up from the Bodélé Depression in Chad, an ancient lakebed where rock minerals composed of dead microorganisms, is loaded with phosphorus.”

Now let’s move, briefly, to the Pacific Ocean. USA TODAY’s Dinah Voyles Pulver wrote regarding that mammoth region: “The world’s most influential climate pattern is baring its teeth in the Pacific.” That pattern is El Niño, which is a natural warming of seawater that influences weather around the planet and is now setting daily warm water records. El Niño’s effects on global temperatures increase the chances that 2026 could be the warmest year on record and make it likely that 2027 will be even warmer. But, curiously, that climate pattern is widely expected to tame the 2026 Atlantic hurricane season. My advice is to stay tuned.

by Paris Reidhead