Andrew, I'm not sure this is entirely explained by migrating birds.
It looks like most of the targets northwest of Philadelphia appear to have velocities of 5kts or less, which is indicative of ground clutter. This occurs when the radar beam is bent back down towards the earth's surface and hits objects on or near the ground...like leaves, insects, (maybe birds migrating?) etc.. Inversions (where temperatures increases with height) just off the surface are notorious for bending the radar beam back down towards the surface. The 00z sounding out of Upton, NY (I didn't really dive into how representative it is of the region though, but it looks okay after a quick glance) showed a modest inversion up to about 900mb...shown here if you get this before 9-10AM ET Thursday... http://www.rap.ucar.edu/weather/upper/okx.gif Presumably, some of this ground clutter could be migrating birds since it does seem to increase as the evening wears on, but the velocities are somewhat perplexing. Maybe the background noise of leaves, insects, etc. are not allowing the radar to pick up on the velocities of the migrating birds, which should be in the 15-25kt range? The increase in reflectivitys during the evening hours could also be due to the inversion strengthening with the onset of nighttime cooling. Colby On Wed, Oct 27, 2010 at 7:54 PM, Andrew Albright <[email protected]>wrote: > To radar watchers out there, does anyone care to comment on the > reflectivity radar loops tonight for the area 10-20 miles northwest of > Philadelphia? > > 1. On the ground, I've heard and recorded a lot of longer "tseeps" > (20-50 for some minutes) - which is more than I've ever heard around > here. I'd have to guess most sound sparrowish (white-throated and plus some > short ones) - so nothing surprising given the time of year. > > 2. There's not much wind but what there is out of a southerly direction (it > feels like Florida right now here) so not what I would think would be > favorable for a heavy migration. > Although if you look at the surface streamlines, it looks like we are on > the edge of a change in wind direction/speed: > http://homes.comet.ucar.edu/~guarente/birdweather/stream.htm > The upper level wind direction is definitely out of the southwest. > > 3. There's rain in the area and I see a lot of green on the radar* (not > blue) - so I'm having a hard time. > > Sincerely, > Andrew Albright > > *Using http://www.rap.ucar.edu/weather/radar/ > -- NFC-L List Info: http://www.NortheastBirding.com/NFC_WELCOME http://www.NortheastBirding.com/NFC_RULES ARCHIVES: 1) http://www.mail-archive.com/[email protected]/maillist.html 2) http://birdingonthe.net/mailinglists/NFCL.html 3) http://www.surfbirds.com/birdingmail/Group/NFC-L Please submit your observations to eBird: http://ebird.org/content/ebird/ --
