It happens each spring; the huge nocturnal (night) migration of ducks, geese, swallows and all those other birds from warmer regions on our planet to northern/cooler areas. Think about this; there are probably birds flying right over your home tonight that will end up spending the warm season in the Yukon or even near the Arctic Ocean! Oh, and they may have spent the winter in Mexico or Costa Rica too. That part doesn’t sound too bad does it?
Because birds are large compared to precipitation (rain/hail/snow) they show up quite well on radar and it doesn’t take that many to trigger an “echo” on the radar screen. Of course you might be wondering like me why we don’t see birds on the radar screen all through the warm season? We usually don’t because those birds don’t have any reason to move high up into radar range (more than a thousand feet or so). But when migrating they go high to avoid low-level wind fields, instability, and denser surface air. Tonight is a great night for them since there is a solid south/southeast wind ahead of the approaching cold front.
They are quite visible on the “VAD” wind display. That’s the wind profile the past couple of hours from the Portland radar. The radar is located up around the 2,000′ elevation just west of Scappoose.
Time goes from left to right. Look at how the targets rise quickly in elevation right after sunset. Note it says 50 knots! That’s likely the 20-30 kt southerly wind plus the motion of the birds. It’s also fascinating that the highest echoes (birds) gradually increase in altitude…those guys are working hard to get up to their “cruising altitude”. Ducks have been known to fly up around 30-50 mph even under calm conditions. They can cover 800 miles in one night if they really want to.
This is what it looks like on the “regular” radar screen as the birds take off, from an earlier blog post. Note they don’t like to fly over water. The Ocean Shores radar on the Washington coastline shows almost all “bird action” tonight is over land.
One final note, the dual-pol radar is pretty good at detecting the type of “target” we are seeing in the sky. Note the current display shows almost all “BI”. That means BIOLOGICAL. It could be insects, but not in this case.
By the way, there is a movie called WINGED MIGRATION (a documentary) produced about 10 years ago using hand-raised birds. They follow the birds (usually geese) while flying and migrating using some sort of very light aircraft. Or, actually I suppose the birds follow the aircraft since they imprinted on humans at hatching. That means they think humans are part of their family. Now, believe me, this is no “party movie”, actually it’s REALLY slow, but great visuals for little kids to watch. Filming was done all over the planet. Here’s a clip for a little evening relaxation:
Chief Meteorologist Mark Nelsen