Forecast and Analysis

Regional Migration Analysis: 18-24 May 2013

Andrew Farnsworth The Cornell Lab May 24, 2013

Continental Summary:

Primarily light movements occurred in the West as the clock on this season’s migration continued to wind down, while moderate to locally heavy movements continued in a number of areas East of the Rockies. Birds on the move this week included Ruddy Turnstone, Olive-sided, Willow and Alder Flycatchers, Cedar Waxwing, and Mourning and Wilson’s Warblers.



Light movements occurred in many areas, particularly southern and western portions of the region, to begin the period. However, movements dropped off to begin these week in all but the southernmost reaches as strong high pressure built over the northern Rockies. As high pressure dipped south, and winds calmed, more widespread light and locally moderate movements occurred on Monday night. This pattern of more widespread light movements gradually diminished in extent and intensity as the week progressed, with local and scattered precipitation shutting down movements. Birds on the move this week included Western Wood-Pewee, Willow Flycatcher, Eastern Kingbird, Gray Catbird, and Yellow Warbler as western portions of the range of many eastern species’ distributions filled.

Great Plains

Moderate and locally heavy movements were widespread to begin the forecast period, although increasing precipitation associated with an organizing set of low pressure centers shut down movements where it met migrants. As a frontal developed and moved East, migration shut down in much less favorable conditions to begin the week. As conditions improved over the days that followed, increasingly more widespread moderate movements occurred, punctuated by locally heavy movements in the border states. By the end of the period, widespread light to moderate and locally heavy movements spanned the region, increasing with increasing proximity to the Canadian border. Birds on the move this week included White-rumped Sandpiper, Yellow-billed Cuckoo, Olive-sided and Alder Flycatchers, Mourning, Tennessee, Canada, and Cape May Warblers, and Orchard Oriole.

Upper Midwest and Northeast

High pressure over the central Mississippi River valley and central Appalachians spawned moderate to heavy movements in western portions of the region, while the Northeast and coastal plain was quiet. As a frontal boundary formed and stalled across the region, light to locally moderate and heavy movements were spread over most of the region. Note that precipitation kept birds grounded in more southerly areas, as more intense movements occurred farther West. The general pattern of widespread light to moderate and locally heavy movements away from precipitation followed into the middle of the week, defined in large part by the distribution of nightly rain, in a complex patchwork pattern of migration and groundings. By the end of the week, the picture became clearer, as a strong frontal boundary pushed East and gradually shut down the system by Thursday night. Birds on the move this week included Olive-sided, Alder and Willow Flycatchers, Cedar Waxwing, and Canada, Wilson’s, Mourning, and Blackpoll Warblers.

Gulf Coast and Southeast

Moderate to heavy movements began the week in Texas, while light to moderate movements were scattered across the remainder of the region away from precipitation. Movements became less widespread and less intense over the remainder of the forecast period, and particularly noticeable was the decreasing extent of these movements in the Southeast. By the end of the week, movements were mostly occurring in the westernmost reaches of the region, and in light to locally moderate levels at best. Birds on the move this week included Black Tern, Sanderling, Ruddy Turnstone, Cedar Waxwing, Gray-cheeked Thrush, and Mourning Warbler.