Forecast and Analysis

Migration alert: easterly winds in the North Atlantic

Andrew Farnsworth The Cornell Lab Oct 16, 2020

Today, we focus briefly on developing conditions that may bring European species (for example, Northern Lapwing) west across the North Atlantic into the Canadian Maritimes. BirdCast has discussed this pattern and associated conditions previously, and additional background is here in this post. These conditions are not predicted to last for many days, but birders in northeastern North America should be aware of the short term forecasts and spend some quality time in the field (you should probably be doing that anyway, and submitting your observations to eBird!). The two maps below from highlight the patterns of interest: first, in surface level winds and second, in 925 millibar (a.k.a. ~2,500 ft above the earth) winds.

Note a strong pattern of flow from a generally easterly direction to the west of Ireland and continental Europe. The potential for these winds to displace European species is greatest for this weekend and early in the week, dissipating markedly after that with the movement of a strong frontal boundary across the Atlantic. Generally, such patterns of easterly flow across the Atlantic are associated with negative phase of the North Atlantic Oscillation (a Northern hemisphere relative of the Southern Oscillation we know well from discussions of El Niño and La Niña cycles), in which high pressure establishes near Greenland or in close proximity in the North Atlantic and circulation around such a pressure center brings prevailing easterly winds across (e.g. in the below map during Saturday forecast periods, see wind circulation around the high pressure “H” south of Greenland).

Surface-level winds

925MB, ~2500 ft above ground level