Forecast and Analysis

Regional Migration Analysis: 4-11 May 2013

Andrew Farnsworth The Cornell Lab May 10, 2013


Light to moderate movements across much of the West exemplified more of the steady push of birds into the region, while the East received a jolt of birds midweek, including some movements into the Northeast after many days with a trickle. Birds on the move this week included Least Flycatcher, Warbling Vireo, Gray Catbird, Yellow Warbler, and Baltimore Oriole.



Light to moderate movements were the norm is many areas from the beginning of the period through the early part of the week. This was particularly true in the Desert Southwest and for much of the Pacific Coast. Some scattered precipitation inhibited movements from northern California East and South through the central Rockies by Monday night. However, the influence of this passing disturbance was short-lived, as light to moderate movements continued for much of the remainder of the period. Birds on the move this week included Wilson’s Phalarope, Western Wood-Pewee, Warbling Vireo, Swainson’s Thrush, MacGillivray’s Warbler, Western Tanager, and Black-headed Grosbeak.

Great Plains

High pressure kept most birds on the ground to begin the forecast period, with the exception of some locally light to moderate and even isolated heavy movements in the Dakotas. By late in the weekend, light to moderate movements became more widespread, and by Monday night moderate to heavy movements occurred in many areas. Despite local precipitation on Tuesday night, migration continued as these levels in precipitation free areas. As the precipitation continued, and instability in the atmosphere grew, some movements were diminished in more northerly areas and shut down altogether in storms over Kansas. The many species on the move this week included Common Nighthawk, Least and Great Crested Flycatchers, Swainson’s Thrush, Gray Catbird, Palm, Orange-crowned, Tennessee, Yellow and Blackpoll Warblers, American Redstart, Clay-colored, Lincoln’s and White-crowned Sparrows, Indigo Bunting, and Bobolink.

Upper Midwest and Northeast

Light movements East of the Mississippi were local and isolated to begin the forecast period, in advance of an approaching frontal boundary. This pattern continued as the front stalled, and high pressure brought generally marginal and unfavorable conditions for most movements across the region. On Tuesday night, after much of the same marginal to unfavorable conditions, high pressure over the Great Lakes allowed some scattered moderate to heavy movements to occur from the western Great Lakes south along the Mississippi River valley. Local and scattered moderate to heavy movements expanded on Wednesday night from New York South and West through Kentucky. However, precipitation scattered locally from Virginia North and East through the Great Lakes and New England and associated with a weak low pressure center moving off the DelMarVa coast shut down movements in some places. Interestingly, this weak low pressure system presumably spawned some intriguing waterbird fallouts, including reports of Red Phalarope and Arctic Tern in inland locations. Thursday night saw another influx of locally moderate and heavy movements as the effects of the weak low pressure system continued, with the first southerly flow in many different areas creating movements in concert from Virginia through Massachusetts (particularly along the I-95 corridor). Birds on the move this week included Least Flycatcher, Warbling Vireo, Gray Catbird, Cape May, Chestnut-sided, Magnolia, Nashville, Blackburnian, Golden-winged, and Bay-breasted Warblers, White-crowned Sparrow, Rose-breasted Grosbeak, and Baltimore Oriole.

Gulf Coast and Southeast

A cold front sweeping across the region shut down western Gulf of Mexico migration, as locally light to moderate movements occurred farther East of the frontal boundary. As the front continued to push slowly East, light to moderate movements returned over Texas and Louisiana. By Saturday night, a complex pair of fronts were over the region, spawning moderate to heavy movements in Texas, light to moderate movements over Mississippi and Alabama, and shutting down most Florida movements. The situation organized and simplified to begin the week, with high pressure dominating over the Great Plains and producing marginal conditions for widely scattered and highly localized moderate to heavy movements. While this pattern continued over the Southeast, more widespread moderate to locally heavy movements occurred over Texas on Tuesday night. This pattern intensified and expanded East through midweek to the end of the forecast period, with moderate to heavy movements becoming more widespread. By Thursday night, a frontal boundary moving into the panhandle of Texas was already causing some instability toward the coast, with strong storms setting up localized fallouts from the Upper Texas Coast through the lower Mississippi River valley. The precipitation also created another intense fallout scenario for trans-Gulf arrivals on Friday, as intense storms sat right off the coast as migrants arrived onshore in the middle of the day. Birds on the move this week included White-rumped Sandpiper, Yellow-bellied and Least Flycatchers, Eastern Wood-Pewee, Gray-cheeked and Swainson’s Thrushes, Mourning, Magnolia, Canada, Blackpoll, and Chestnut-sided Warblers, and Scarlet Tanager.