Tuesday, May 6, 2008

Crowded Skies Tonight

It's that time of year again - when migrating birds clutter radar screens across the country during night migration. Check out previous posts on the subject for review here. For good radar loops see Rutgers Weather Center.

Before nightfall
11:00PM Eastern Time - the wave reaches the Great Plains

Click to animate

Update: migration spreads farther west

Migration winds down in the morning - 5am Eastern time

8am Eastern time


  1. I have a question. How do you tell the difference between birds and weather on the radar images? I've been trying to figure that out for a while and I can't quite figure it out.

  2. This evening, shortly after dusk, watch the national radar loop. The difference is most apparent when you see it animated - the birds appear in large wave moving across the country as night falls. The radar signatures of weather and birds are still distinctly different once you have an eye for it.

    Look at this image for example:

    Birds show up as circular blobs of low return centered on each radar station - for example, the blob centered around buffalo. Weather is never circular, it is irregular, much stronger patches, such as the SW-NE storm line across the midwest in yellow and green, and it moves. Bird migration stays centered around each radar dome - because of the low return values the radar only picks up the birds within a certain distance of the dome.

    In some cases, the bird migration is so heavy that the radar can look like it is weather - as appears to be the case in south texas and florida. I'm not sure whats going on in california but I think it is strong migration up the central valley - they must have enough radar points to make it appear as a blob rather than a circle.

    If that still isn't clear to you, all you need to do is watch the radar change at dusk - radar returns will suddenly flare up across the country, if it is a strong movement night. On nights when it isn't so good, you can often see just pockets of migration in certain areas of the country. Last night was exceptional in that birds were moving everywhere. There is a gap in the coverage over CNY though because the radar dome was down.


  3. It's pretty insane that these birds are travelling in such numbers that they can be picked up on radar. Thanks for that informative comment as well.

  4. Hi Nick,
    I really like this site you are probably aware if anyway but, here it is:
    Images begin to show up about 1/2 hr after sunset.

    Good birding. :)

  5. Nick, I really appreciate the detailed explanation. That will really help. I will try that tonight.

  6. I live in north central Texas, right beneath the migration path of the Whooping Cranes as they make their way down to the sanctuary near Port Aransas on the Gulf of Mexico every fall. I will never forget that one bright day when I stepped out of my office for lunch at just the right time to see about three hundred of them in broken groups swirling and wheeling up above. I live in a city surrounded by lightly wooded wetlands and I can only assume it's a great pit stop for some fish or frogs on the go ;)