John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Warning: This footage might make allergy sufferers sneeze their brains out.
Tony Nettles of Palmetto Weather captured the awful allergy-mist this week using an infrared camera. While single pollen grains are often too small to be noticed, here they appear to have clumped into flakes that, if hoovered into a sinus, would cause sneezing fits for hours.
“Pollen grains are very sticky and easily stick together when they collide,” says Nettles. “You’ll notice in the video that these clumps are falling downward. A single grain of pollen would be so lightweight that it would likely stay airborne. You need many of them clumped together in order for them to be heavy enough to fall with gravity like this.”
But that’s not the only fascinating thing about South Carolina’s recent explosion of pollen. The particles have drifted so thickly they appear to have tricked weather instruments into actually believing they’re snow. The evidence comes from an automated weather sensor’s log for March 22 in Columbia, showing several hours of snow despite clear skies and above-freezing temperatures.
The local office of the National Weather Service has also noted reports of snow and “low clouds” due to pollen. For weather geeks who want the nitty-gritty on this bizarre phenomenon, Nettles explains more via email:
These ASOS stations have a device called a LEDWI (Light Emitting Diode Weather Identifier) which basically consists of a beam of infrared light that measures the size, shape, intensity, and fall pattern of precipitation as it falls through that beam of light. It can tell by the size, shape, and fall pattern if the particles are raindrops or snowflakes (as liquid raindrops stretch to a long/skinny shape as they fall through the air and quickly fall straight down, while snowflakes are more fat/round and tend to wobble/drift in the wind as they fall). The pollen, being a lightweight solid, is round and drifts in the wind much like a snowflake.
It also compares this with other data sensors (such as the thermometer) on the ASOS station in order to quality-control the reports. That is, if the thermometer says it’s 70 degrees, it will know it’s too warm for snow and will discount any suspect snow signatures falling through the light beam. Temperatures dropped into the 30s this particular morning—a reasonable temperature for snow. Thus, it fooled the quality-control algorithms that typically block pollen from being reported as “snow.”
So while Northerners are battling a winter that won’t die this spring, at least they haven’t had to suffer misery like this in the South:
And while this footage from Tennessee comes from a few years back, it simply cannot be omitted from any discussion of the pollen count being high: