David and others, You were asking about where to get archived soundings/wind data. There is a lovely archive at the University of Wyoming's website here:
http://weather.uwyo.edu/upperair/sounding.html and equivalent archived upper-air maps here: http://weather.uwyo.edu/upperair/uamap.html and real-time profiler data here (only found over the Great Plains): http://weather.uwyo.edu/upperair/profiler/ >From there you can select an image type (stuve or skew-t is likely preferred, but hodographs are available as well if that is what you know how to read). Then select the date and time (remember it is all in UTC) and then a location. There are soundings here for all over the globe, so this isn't a bad site to have on hand for investigating other sites outside the US. You don't need to know the number of the sounding station, you can just click on it on the map. If you select stuve or skew-t the winds will be up the right side and those correspond to the heights and pressures listed on the left side of the chart. Here are the soundings from Omaha, NE and North Platte, NE for the closest times to Bill's original observations. Note the significant difference in winds in the low levels. Omaha shows a strong north-northwest wind, while North Platte shows a highly variable wind direction and light winds at low levels. This suggests exactly what David and others have theorized about. Omaha: http://tinyurl.com/3nbtoyv North Platte: http://tinyurl.com/3gwtu48 Another way to look at this, although not observations is to look at the streamlines from recent model output. I plot streamlines on my website here: http://homes.comet.ucar.edu/~guarente/birdweather/stream.htm I unfortunately have not set up an archive yet for my site due to space limitations, but I might be able to rerun that date to show the effects seen in the soundings and on radar if anyone wants to see it. This kind of pattern often happens with the passage of weak fronts. The winds start to either turn around quickly due to local effects or the winds are so weak behind the front that migration can easily occur even in the face of a northwest wind albeit light. (opinion) I personally think that most bird migration discussions focus a lot on long distance migration nights more than they focus on those localized events that can sweep out all the recent migrants from a small area or those that bring in a small push of birds very close behind a front despite the winds being out of the wrong direction. For this reason, I am contemplating adding winds speeds to my streamlines maps, but it is currently unclear to me the best way to visualize this from model data because the winds are so variable that the map gets way too complicated for most individuals to read. I might do some averaging to get a broader look at the winds, but there are some hits taken by doing that. We'll see what I can pull off sometime with my extra time. 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/ --
