Light and variable surface winds coupled with light WSW winds aloft resulted in a moderate migration event across the northeastern US and mid-Atlantic last night. Here’s the radar from 7:30pm last night through 5:00am this morning. Note that the Dover, DE radar was down for maintenance last night so no radar was available for that station.

Frames are every 1/2 hour. Click on the thumbnail to view the full-sized animation.

  

Looking at the national composite you can get a broad view of migration density and see that the northeast and mid-Atlantic, while active last night, were clearly eclipsed by the large migration events to our south and west. Migration over the northeast and mid-Atlantic was thinner and more truncated than the surrounding areas, likely due to the less-than-optimal atmospheric conditions. In most cases across our region, birds were traveling either without assisting winds or even into a slight opposing wind. Given how light the winds were neither of these scenarios pose much resistance to a migrating bird- although we know from our research that both bird density and length of flight tend to be higher on nights with a tailwind.

Looking at the individual radars for NYC and Fort Dix, we see that the WSW upper-level winds were having an influence on migrants. Over NYC only a small proportion of the reflectivity appears to have been birds heading SW while the majority of reflectivity appears to be heading to the NE. Given that the upper-level winds were 10-15kts out of the SW, and the targets on the radar were moving up to 25kts, this suggests that some of the reflectivity represents reverse migration into eastern Long Island, NY.

Over New Jersey we see a similar scenario, with the major axis of movement running with the upper-level winds (generally W->E) but with most of the reflectivity showing a WNW->ESE trajectory. This most likely represents birds moving against a slight side/headwind but generally heading south along the coast. Given this scenario, I would expect coastal location to see more birds this morning- especially Cape May. Southwest winds throughout the day, while not good for diurnal migration such as raptors, does hold the potential for some interesting arrivals to the southern peninsula (such as an increase in swallow diversity and numbers).

Good Birding

David