Forecast and Analysis

Regional Migration Forecast 18-24 May 2013

Andrew Farnsworth The Cornell Lab May 17, 2013


Light to moderate movements continue in many portions of the West, as moderate to heavy movements shift increasingly farther North in the East in areas away from precipitation. Heavy movements in the southern US will begin to wane over the course of this week and next as we near the end of another migration season. Birds on the move this week will include Semipalmated and White-rumped Sandpipers, Willow, Alder and Yellow-bellied Flycatchers, and Bobolink.



The Desert Southwest will experience light to moderate movements to begin the weekend, as the remainder of the region will see only local light movements away from precipitation scattered from the Pacific Northwest through the northern Rockies. This pattern continues through the early part of the week, when conditions become more favorable across the region for light to moderate movements. Favorable conditions persist for light to moderate movements for most of the region through the end of the forecast period, with the exception of the Pacific Northwest and portions of the Rockies, which will see precipitation and migration shut downs later in the period. Note that numbers of birds aloft at night will begin decreasing markedly over the course of this week and next week, as migration passes peak in many areas for many species. Birds on the move this week will include Alaskan waterbird arrivals (e.g. Long-tailed Jaeger), Willow and Hammond’s Flycatchers, Western Wood-Pewee, Swainson’s Thrush, and Orange-crowned and MacGillivray’s Warblers.

Great Plains

Moderate to heavy movements will occur over the weekend as migration nears or passes peak for many species, with the potential for fallouts in more northerly areas as a frontal boundary intersects with northbound migrants in the Dakotas. This pattern continues into the early part of the week, with the possibility for fallouts expanding south to include some areas in the central and southern Plains. By midweek, the pattern changes as low pressure moves East across the border states – migration will continue to be moderate to heavy in many areas, given the date and light winds, but more areas will see a decrease in birds aloft at night. Localized fallouts are still likely as precipitation is forecast in several parts of the region. The end of the forecast period sees an interesting set of conditions, likely allowing moderate to heavy movements to continue farther south and away from precipitation but largely dividing areas of heavier movements to the south from lighter movements to the north in an area where fallouts may occur. Birds on the move this week will include Ruddy Turnstone, Black Tern, Common Nighthawk, Alder Flycatcher, Canada Warbler, and Bobolink.

Upper Midwest and Northeast

Scattered precipitation shuts down many movements over the weekend, although areas away from precipitation will experience moderate to heavy movements. Birders should be listening for nocturnal migrants in areas where cloud cover is extensive, and as usual birders should be watching carefully the distribution of nocturnal precipitation: passerine and waterbird fallouts are still likely in places where migrants encounter rain. Monday night will see more widespread moderate to heavy flights, particularly if precipitation is more limited than forecast. However, the course of the remainder of the week is complicated by the forecast for rain in many areas. Areas free of rain, even if for several hours at night, will experience moderate to heavy flights, so continued attention to the potential for fallouts later in the week is warranted, particularly in the Appalachians. By the end of the week, precipitation is organized sufficiently to shut down movements in many areas, although, again, areas away from precipitation (particularly in the Great Lakes and New England), will continue to experience moderate to heavy flights despite marginal conditions. Birds on the move this week will include Semipalmated Sandpiper, Ruddy Turnstone, Willow and Alder Flycatchers, Cedar Waxwing, and Mourning and Canada Warblers.

Gulf Coast and Southeast

Late season trans- and circum-Gulf migrants will move in moderate to heavy overland flights for the weekend through the middle of the week. Areas of precipitation, though away from the coast, will bring localized concentrations and fallouts in several areas of the Southeast over the course of the forecast period, so as usual birders should watch the distribution of precipitation carefully. By the end of next week, conditions deteriorate in many areas of the Southeast, with increasing precipitation and increasingly easterly winds shutting down movements in many areas. However, the easterly flow may make for interesting birding in more western coastal areas, with the potential for some displacement of later season Caribbean system migrants to the West. This week harkens the onset of markedly fewer passage migrants in the system, given the date, but birds on the move this week will continue to include later season shorebirds like White-rumped and Semipalmated Sandpipers and later season passerines like Alder and Yellow-bellied Flycatchers, Gray-cheeked Thrushes, and Mourning Warbler.