[Tweeters] Evening migration on NEXRAD radar

Doug H dhudson at silverlink.net
Mon Oct 19 20:29:04 PDT 2009

8:00 PM,

A classic evening migration can be seen at this hour on NEXRAD radar. I started watching about sunset this evening. At that time one could see birds were crossing from the area of Sooke on the south end on Vancouver Island to an area west of Port Angeles. Another line was seen from the Victoria area to Port Angeles and Sequim. A much larger line was noted from the Vancouver, BC area down across Bellingham, Everett, Seattle and continuing south. Early on there was a clear line with no birds over the water between the main land and land masses on the west side of the sound.

Here is a link to all the NEXRAD stations across the country: http://www.rap.ucar.edu/weather/radar/ Click on the station to the north of Seattle. It will come up in the reflectivity mode which will show the overall mass of birds. There is little to no precipitation in the area this evening so most of what you will see is birds. The velocity mode is more interesting and can be seen by clicking on the reflectivity image. In the velocity mode you will note shades on blue to the north and shades of yellow to the south of the station. The blue indicates birds flying toward the radar while the yellow shows birds as they fly away from the radar. The speed will generally be between 10 and 30 knots.

All of this is best seen with no precipitation which is often not the case in our area. For those who find this interesting, click on a radar station in a Great Planes state about local sunset. You will see a fuzzy area around the radar as birds take to the sky. Over the next 45 minutes or so you will see the fuzzy area get larger and larger as more and more birds come into the radar field. Again, click on the image to get to the velocity mode where you can appreciate the direction of flight. Keep in mind the radar can not detect birds down in the trees or very low to the ground. The higher the birds, the farther they can be detected depending on their reflectivity. One can also see insect migration with NEXRAD radar. In that case the velocity is much lower so it is rather easy to tell the difference.

Doug Hudson
Bremerton, WA
dhudson at silverlink dot net
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