Ted and other interested parties, I ran the HYSPLIT model (page to runyour own HYSPLIT) on your Sept 29, 2008 date to see what the 6-hr backward trajectories would look like to get to your patch by 6AM. The corresponding plots are here:
http://ready.arl.noaa.gov/hysplit-bin/trajresults.pl?jobidno=385220 You can take a look at those in Google Earth or Google Maps for best discrimination of the 6-hr backward trajectories. If you zoom out and look at the general pattern, there must be a high pressure system rolling in from the northwest as the trajectories seem to fly these birds from Nebraska/South Dakota and back them into the Front Range. I haven't checked the cloud cover or anything like that because you would likely know the information about that from in-situ observations. For further maps, check these out (mean sea-level pressure): http://virga.sfsu.edu/pub/composites/sathts_snd/0809/08092900_sathts_snd_alt.gif http://virga.sfsu.edu/pub/composites/sathts_snd/0809/08092906_sathts_snd_alt.gif http://virga.sfsu.edu/pub/composites/sathts_snd/0809/08092912_sathts_snd_alt.gif There is a frontal passage at about 00 UTC (the first map), then the high pressure system rolls in over time. The frontal passage seems to be the trigger in this case and in a lot of cases with a frontal passage, there is along-front flow like what is backing the birds into the Front Range of Colorado. It is always hard to tell how the along-front flow will pan out as it depends on a lot of factors (location of the bird or birds on the front, depth of front, speed of frontal propagation to name a few). If you can pinpoint a better time for the movements that you wanted to target, we can be even more accurate, but for now this was my crack at it. Bryan Guarente Instructional Designer The COMET Program University Corporation for Atmospheric Research Boulder, CO -- NFC-L List Info: http://www.NortheastBirding.com/NFC_WELCOME http://www.NortheastBirding.com/NFC_RULES http://www.NortheastBirding.com/NFC-L_SubscribeConfigurationLeave.htm ARCHIVES: 1) http://www.mail-archive.com/nfc-l@cornell.edu/maillist.html 2) http://www.surfbirds.com/birdingmail/Group/NFC-L 3) http://birdingonthe.net/mailinglists/NFCL.html Please submit your observations to eBird: http://ebird.org/content/ebird/ --
