Forecast and Analysis

Regional Migration Forecast 4-11 May 2013

Andrew Farnsworth The Cornell Lab May 03, 2013


Unsettled weather across the West and the East complicates the migration scene this week, with light to moderate movements apparent in the West and moderate to heavy movements in the East away from rain. Numerous species are on the move this week, including Yellow-billed Cuckoo, Least Flycatcher, Wood Thrush, American Redstart, Yellow, Magnolia, Blackburnian, and Chestnut-sided Warblers, Bobolink, and Baltimore Oriole.

Forecast May4-11


Light to moderate movements will occur in the Desert Southwest and California to begin the weekend, while more northerly reaches of the region will see less substantial movements in less favorable conditions and some scattered precipitation. These movements become more widespread to end the weekend, as the scattered precipitation dissipates and wind speeds diminish. The beginning of the week sees the beginning of an interesting pattern of scattered precipitation forecast for many areas, and this pattern continuing though the week and even intensifying over the course of the week. Whereas many areas free of precipitation will see light to moderate movements, particularly in the middle of the week, concentrations and fallouts are possible where birds encounter precipitation. Some of the precipitation, particularly later in the week, will be sufficient to shut down movements completely. As is typically the case, bird movements will be primarily visible on radar from the Desert Southwest and California. Birds on the move this week will include Western Wood-Pewee, Swainson’s Thrush, Yellow, Wilson’s and MacGillivray’s Warblers, Western Tanager, and Black-headed Grosbeak.

Great Plains

Generally unfavorable conditions continue over the Great Plains to begin the period, but given the date, widespread moderate movements will likely occur. Some of these movements, particularly in areas with lighter winds, will be locally heavy. Border states will see a reprieve by midweek, with more favorable conditions for moderate to heavy movements, but precipitation in more southern areas likely continue to inhibit most heavier movements. Wednesday night is forecast to be the most favorable night of the week for movements, with widespread moderate and heavy movements likely. Conditions deteriorate thereafter through the end of the period, with precipitation in the forecast and migrants moving only in areas free of precipitation at moderate to heavy levels. Birds on the move this week will include White-rumped and Stilt Sandpipers, Common Nighthawk, Yellow-billed Cuckoo, Eastern Wood-Pewee, Gray Catbird, Yellow, Blackpoll, and Tennessee Warblers, Rose-breasted Grosbeak, Bobolink, and Orchard and Baltimore Orioles.

Upper Midwest and Northeast

To begin the period, this region will experience several days of marginal conditions for migrants. Although winds will be light in many areas, the directions are not seasonably favorable for intense movements to occur. However, given the time of year, light winds regardless of direction will allow for moderate to heavy movements in many areas. Presumably, these will be biased toward inland flights, rather than coastal flights. By Tuesday night, the Northeast should experience moderate to locally heavy movements in many areas. Midweek sees the arrival farther to the south and west of a low pressure system, shutting down movements as precipitation falls in a number of areas south of New York and New England. Even as this system passes, conditions will remain marginal through the remainder of the period. Movements will be moderate to locally heavy in areas with light winds, and as usual, birders should pay particular attention to places where birds encounter precipitation for fallouts and concentrations. Later in the week, birders should also pay articular attention to inland bodies of water, as precipitation will mean waterfowl and waterbird fallouts. Among the numerous birds on the move this week will be Acadian and Least Flycatchers, Eastern Kingbird, Wood Thrush and Veery, Magnolia, Chestnut-sided, Wilson’s, and Black-throated Blue Warblers, Rose-breasted Grosbeak, Scarlet Tanager, and Baltimore Oriole.

Gulf Coast and Southeast

East of the Mississippi, migration will shut down to begin the weekend as widespread precipitation will keep birds on the ground. Clearer skies to the west of the Mississippi will allow for mostly light to moderate but some locally heavy movements to occur, despite less than favorable winds in many areas. This pattern continues through the early part of the week, when the low pressure system finally exits to the east and more favorable conditions return to the western and central Gulf of Mexico (and points south of there). A more substantial trans-Gulf flight will initiate on Wednesday night, as will moderate to heavy movements west of the Mississippi River valley. This pattern intensifies through the end of the week, although the Southeast remains generally unfavorable for most movements to occur. By week’s end birders should watch the path of a forecast low which will approach the coast closely, possibly bringing rain near the coast and the potential for fallouts. Forecasts at present do not suggest that this will happen by Friday 10 May. However, fallouts at the edge of the coastal plain will be possible in numerous areas, something we will discuss more in next week’s forecast. Among the many species on the move this week will be White-rumped Sandpiper, Yellow-billed Cuckoo, Olive-sided Flycatcher, Wilson’s, Mourning and Magnolia Warblers.