Migration (or not) Alert, sponsored by the polar vortex

Andrew Farnsworth The Cornell Lab May 08, 2020

Global Big Day is here, and hopefully citizens of the world will observe a huge percentage of the planet’s avifauna from the physically distant confines of homes, yards, windows, porches, and all the other places to be safely distanced! Here in the US, in the lower 48 states, we have an exciting or depressing migration dichotomy brewing. We remember well presumably the dread associated with a weak¬†polar vortex¬†that allows (often very) cold Arctic air to escape into the continental US.

Here we are in May, at the peak of bird migration in many areas, and here we have the potential in many areas of the eastern US to set record cold temperatures! With snow no less! And so too to continue high temperatures in the western US! The graphic below is one way to represent where these extremes will occur, by mapping geopotential heights to highlight where anomalously cold (blue) and warm (red) temperatures will occur.

If you study this map with respect to the migration forecast for 8 and 9 May 2020, you will see some of these striking patterns mirrored in the forecasts! Note that the broad areas of the East where little to no migration is forecast corresponds to the low temperature anomalies and generally winter like conditions not conducive to spring migration. So too areas of the West, particularly the Pacific Coast, are predicted to experience medium intensity movements in favorable conditions, in fact in some areas far above normal temperatures. And at the boundary between the two anomalies, in the Great Plains? We see conditions that are probably marginal but sufficient to allow for the typical spring intensities to continue. (And Texas coast … watch the passing frontal boundary for coastal fallouts!)

Good luck with your birding, be safe and responsible with your physical distancing, and don’t forget to submit all of your observations to eBird!