A spring overshoot discussion . . . continued.

Andrew Farnsworth The Cornell Lab Apr 04, 2013

Several weeks ago, Team BirdCast highlighted a set of conditions for spring overshoot migrants, or “slingshot” migrants, to occur substantially farther north of their intended and seasonally appropriate destinations. We see potential for such conditions over the coming 24-48 hours, as a cold front moves across the Florida Peninsula during a period when early southern migrants are on the move from the Caribbean into the southeastern US.


The evening synoptic weather map shows a frontal boundary bisecting Florida, with an area of precipitation approaching the Gulf Coast of the state. Winds in advance of this front will be southerly and southwesterly, and this flow has the potential to entrain birds moving from points farther south in the Caribbean toward to the US mainland.


As of 10pm EDT on Thursday 4 April, birds are on the move over Florida as precipitation associated with the frontal boundary approaches from the west. Of particular interest is the exodus of migrants from Cuba, as evidenced by the light blue stippled pattern appearing just north of Havana and the Cuban coast. Will these birds fallout in Florida as precipitation moves east, or will some of these birds get swept into the strong flow ahead of the rain and become southern overshoots in New England or the Canadian Maritimes?


The forecast for the morning of 5 April looks enticing for the overshoot scenario, with strong southwesterlies blowing off the Southeastern US coast right into the heart of a developing storm system off the Mid-Atlantic.


This discussion would not be complete without an air parcel model from the READY website. An air parcel beginning at 500m above ground level off the Florida coast at sunset on 4 April travels North and East away from the coast, presumably following a path similar to any birds entrained in the storm system moving across Florida.


However, even more compelling is an air parcel’s path originating slightly farther up the coast. Canadian Maritime arrivals of southern overshoots become an intriguing and even realistic possibility!

Of course, this discussion can only mean one thing, really: you must go forth and find birds. A typical suite of southern overshoots may include Prothonotary and Hooded Warblers, Blue Grosbeak, Indigo Bunting, and Summer Tanager among others. Please submit your sightings to eBird, particularly those of you birding in the Florida Keys and along the immediate Atlantic coast from Florida north through New England to Nova Scotia.