You could see the angels flying over Southern California on Tuesday night.
When National Weather Service radar picked up a giant blob moving swiftly over southwestern San Bernardino County, east of Los Angeles, around 8 p.m., forecasters at the agency's San Diego office called spotters on the ground, who told them it was an enormous swarm of ladybugs.
The weather service told the Los Angeles Times that the ladybug "bloom" appeared to be 80 miles by 80 miles, flying at 5,000 to 9,000 feet.
Since the 1990s, the weather service's parent agency, the National Oceanographic and Atmospheric Administration, or NOAA, has deployed 159 super-detailed Doppler radar installations called NEXRAD, for Next-Generation Radar.
About 10 years ago, it upgraded the system with what it calls Super Resolution, which allows vastly more detailed imagery. The imagery is so detailed, in fact, that it frequently picks up so-called non-weather targets like the ladybug swarm on Tuesday.
In addition to insects, NOAA technical documents say NEXRAD can pick up buildings, wind farms, migrating birds, road traffic and even sunrise and sunset, which will "show up on National Weather Service radar screens as a spike in the direction of the sun."
The weather service even has a name for them: "angels" — radar echoes caused by birds, insects and any number of other anomalies. It turns out they're quite common:
- In August 2010, "curious expanding doughnut patterns" on the radar in Wilmington, Ohio, turned out to be "roost rings," which occur when radar detects thousands of birds taking off from their roosting sites to forage for insects. In this case, the birds were martins.
Weather radar is so good at tracking birds, in fact, that as early as 1998, scientists were studying it as a reliable way to track migration patterns.
- In June 2013, meteorologists in Huntsville, Alabama, detected what they first thought was thunderstorm, even though the sun was shining and there was no rain around. It turned out to be chaff, a cloud of fine metal and glass particles used the by the military — to defeat radar.
- In June 2016, the National Weather Service office in San Antonio, Texas, recorded emerging bat colonies as they woke up and flew out for the evening to eat.
- In 2017, a disturbance on radar in Billings, Montana, was determined to be chairlifts at the Red Lodge Mountain ski area.
"This is actually something you'll see pretty often," Ari Sarsalari, a meteorologist for The Weather Channel, said last month when radar captured a huge swarm of bugs over southern Illinois, southern Indiana and western Kentucky.
When skies are clear, temperatures at the surface can cool off, Sarsalari said. When there's still warm air above it, in what meteorologists call an "inversion," radar beams will reflect downward off it, especially in the spring.
"And that's where all the birds and all the bugs and all that stuff are — they don't go above that layer," he said.