Late February Notes: Migration (or lack thereof) Discussion

Andrew Farnsworth The Cornell Lab Feb 25, 2013

As hinted in last week’s post, there was some potential for scattered light migration across portions of the South-Central and Southeastern US. On 19 February 2013, as a substantial frontal boundary approached the Mississippi River valley, conditions for nocturnal bird migration were favorable in many areas of the eastern Gulf Coast east through the Carolinas. The animation below shows a time series from 7PM EST on 18 February.

For the upcoming week, there are several parts of the continental US that may see light and scattered migration, in particular clear areas where any warm, southerly (or calm) airflow prevails. Some portions of the InterMountain West may see some light movements of early season migrants, so birders should go out to local open water and open country habitats to try to document any such changes.

However, cooler than normal temperatures, particularly in the East, will inhibit most movements for the foreseeable future. The imagery below shows isohypse forecasts from two different models for the 7-10 day period, also suggesting migration will be scant in most areas of the continental US. Cool temperature and generally unfavorable winds, coupled with the early date, highlight the low likelihoods of movements in most areas.

As described in a previous post, isohypse data are useful for identifying potential temperature anomalies. In the case of the images above, we show two different models for the approaching 7-10 day period that suggest a cooler than normal Eastern US and a slightly warmer than normal InterMountain Western US.

Note, though, a potentially more interesting story may relate to the easterlies and northeasterlies forecast for late in the week in the Northeastern US and Atlantic Maritime Canada. In conjunction with an already negative NAO index value, there may be some possibility for a few European vagrants to appear, particularly given the track record of this past winter. Birders in these areas should be watchful, though perhaps not terribly hopeful, as the strength of the negative value and the temporal extent is likely not extreme enough to provide the necessary mechanism to generate such vagrancy.