The Weather Notebook: Birdbursts

Birdbursts
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Dave Thurlow, Host

Birdburst
Imagine yourself a meteorologist looking at your radar screen on a clear, calm morning. Suddenly, something appears on your screen - something really big, a monster of a storm. Wait a minute-that's no storm; it's a flock of birds!

That's right: even the country's newest Doppler radars, which are specially tuned to pick up thunderstorms and snow squalls, can also pick up great crested flycatchers and glossy ibises. Those are birds. Hi, I'm Dave Thurlow and this is The Weather Notebook.

Weather radar uses a wide radar beam, because it's looking for large objects-- like storms-- instead of small objects-- like airplanes. A flock of birds numbering in the hundreds, or thousands (which is common), can cover an area large enough for weather radar to detect it.

This happens most often when flocks leave their nests at sunrise. And it's easier to catch birds on radar as they leave for breakfast because they often leave in big groups, rather than sporadically, one at a time, like they do when they return to roost in the evening.

In fact, the morning bird rush hour is often confused with an important weather. As groups of birds head out every few minutes in all directions, the radar shows a series of concentric rings - similar to the ripples from a pebble tossed into still water.

Scientists call these patterns "Birdbursts", because on radar they resemble what are called "Microbursts" -- or pockets of cool, moist air in thunderstorms that sink to the ground and spread out in all directions, just like the rings.

Now, it's vital for radar technicians to distinguish between Birdbursts and Microbursts. Because while a flock of birds is a harmless phenomenon, Microbursts can bring a jumbo jet crashing to the ground.

Our writer today is Bob Henson. Thanks to Subaru, and to the National Science Foundation.