Masses of lanternflies appearing as rain on radar in Pittsburgh area

PITTSBURGH — If you’ve looked at your weather app the last several days, you may have noticed a “blob” of green on the radar right over the city that doesn’t move. At first glance, it appears to be light to moderate rain, but it’s actually not even weather-related!

The radar beam can detect more than raindrops and snowflakes. When the beam gets sent out, anything from bugs and birds to military chaff can be detected within about 100 miles. In this case, the radar is detecting masses of lanternflies.

How can we be sure this is due to insects?

One of the “dual polarization” modes of radar is called the correlation coefficient, which tells us how similar or dissimilar the objects are that the radar is detecting. Meteorological phenomena such as raindrops will show up as fairly uniform in a dark red or maroon color. However, bugs or “biological material” show up as a low number on CC, or yellow and orange colors, which is exactly what’s been happening this week.

Lanternflies are most common from August through September and are most active during the middle of the day, the same time these “false returns” have been popping up. The bugs thrive in the summertime heat and humidity, so expect more of these returns in the days ahead, especially when it’s sunny.

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