Forecast and Analysis

Regional Migration Analysis 12-17 May 2013

Andrew Farnsworth The Cornell Lab May 17, 2013


Generally favorable conditions across much of the West brought continuing light to moderate movements, but the parade of fronts across the East brought widely varying size and distribution of movements in conditions changing rapidly from day to day. Species on the move this week included Veery, Gray Catbird, Magnolia, Black-throated Blue, Chestnut-sided and Blackpoll Warblers, Common Yellowthroat, and Baltimore Oriole.



Light to moderate movements were the norm this week, as generally favorable or at least marginally favorable conditions prevailed for birds to move across the region. Some areas of California, particularly in the central and northern portions of the state, experienced locally heavy movements early in the period. Not until the mid to late week, specifically Thursday night, did scattered precipitation become sufficiently apparent to locally shut down some movements across northern California and portions of the Great Basin and northern Rockies. Species on the move this week included Olive-sided Flycatcher, Western Wood-Pewee, Swainson’s Thrush, Yellow, and MacGillivray’s Warblers, Black-headed Grosbeak, Western Tanager, and Bullock’s Oriole.

Great Plains

Local but variable movements, ranging from light to isolated heavy movements, were scattered across the region to begin the forecast period, as high pressure moved through the region. By Sunday night, these movements intensified and became more widespread, continuing on Monday night. A passing high diminished movements on Tuesday, but more favorable conditions, primarily driven by light winds, returned for the remainder of the period as more widespread moderate and locally heavy movements occurred. These were tempered, slightly, on Thursday night, as some local precipitation diminish movements in the vicinity of an evolving warm front over the central Plains. Species on the move this week included Mississippi Kite, Black Tern, Yellow-billed Cuckoo, Eastern Wood-Pewee, Gray-cheeked and Swainson’s Thrushes, Magnolia, Blackpoll, Yellow, and Wilson’s Warblers, and Orchard Oriole.

Upper Midwest and Northeast

Moderate to heavy movements were apparent from the central Mississippi River valley East through parts of DelMarVa, and then locally North along the coast into southern New England to begin the forecast period. However, an approaching and a passing frontal boundary shut down migration in all but the most coastal locations by Friday and Saturday nights. High pressure and cooler temperatures building toward the coast kept migrants East of the Appalachians mostly on the ground to begin the week, whereas more favorable and warmer conditions over the Mississippi River valley spawned moderate to heavy movements in those areas. Tuesday night saw many moderate to heavy movements across the region, continuing in some areas through Wednesday night across a stalled frontal boundary. To end the period, this stalled frontal boundary defined areas of favorable conditions and their moderate to locally heavy movements and areas of marginal to unfavorable conditions and their scattered light movements in a striking pattern across the region. Species on the move this week included Least Sandpiper, Yellow-billed Cuckoo, Ruby-throated Hummingbird, Eastern Wood-Pewee, Red-eyed Vireo, Magnolia, Black-throated Blue, Chestnut-sided, Wilson’s, and Blackpoll Warblers, Scarlet Tanager, and Baltimore Oriole.

Gulf Coast and Southeast

Highly variable conditions over the region spawned moderate to heavy movements locally across the region to begin the forecast period. This continued through Friday night, as a well-defined cold front approach the Texas coast, spawning more widespread moderate to heavy movements as it advanced. The region was mostly shut down as fronts pass over the weekend, diminishing movements to local light movements in most areas. To begin the week, moderate to heavy movements returned farther west in the region, over Texas, while the continuing effects of high pressure near the Bahamas kept most movements to a minimum over the rest of the Southeast. As high pressure built over the eastern Gulf and intensified, more favorable conditions became widespread over the region, spawning more widespread moderate movements in many areas. The pattern continued through the remainder of the period, though precipitation associated with low pressure diminished movements locally across the region. Some heavy movements continued in Texas, reflecting a continuing stream of birds arriving from points farther south in continental Central and South America, whereas some drop off in the numbers of birds aloft, particularly over more eastern areas, was and will be increasingly apparent given the date and a diminishing pool of remaining migrants in the eastern Caribbean system. Species on the move this week included White-rumped Sandpiper, Yellow-billed Cuckoo, Common Nighthawk, Olive-sided Flycatcher, Eastern Wood-Pewee, Cedar Waxwing, Blackpoll Warbler, and Indigo Bunting.