Regional Migration Forecast: 29 April – 6 May 2016
Andrew FarnsworthThe Cornell LabApr 29, 2016
Yellow-breasted Chat. C. Jackson/Macaulay Library. 24 Apr 2016. eBird S29176011
Continental Summary
Favorable migration conditions in the latter half of the period for the West will bring extensive light to moderate movements of Spotted Sandpiper, Olive-sided Flycatcher, Dusky Flycatcher, Warbling Vireo, MacGillivray’s Warbler, Lark Bunting, Clay-colored Sparrow, and Chipping Sparrow, while a highly variable period for weather in the East will bring similarly variable and patchily distributed moderate to heavy movements featuring Least Sandpiper, Forster’s Tern, Olive-sided Flycatcher, Least Flycatcher, Acadian Flycatcher, Wood Thrush, Swainson’s Thrush, Golden-winged Warbler, Nashville Warbler, Cape May Warbler, Blackburnian Warbler, and Baltimore Oriole.
Arrows show wind speed and direction (arrow points in the direction to which wind is blowing) 100 m above ground level. Areas with southerly winds are colored red; northerly winds colored blue. Accumulated precipitation (in 6 hour intervals) is green, outlined by white. Broadly speaking, areas of the map in red will experience conditions that are favorable for migration, and areas where red and green (and red and blue) intersect and overlap may experience migrant concentrations and fallouts as migrants interact with precipitation.
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Variable is the word for this period in the region, as generally unfavorable or marginal conditions dominate for at least the weekend and first half of the work week. Movements will be light to moderate in most places, if and when they occur, with highly localized heavy movements where conditions permit. The potential for local migrant concentrations to occur is high in many areas, given the forecast for scattered precipitation and its overlap with locally marginal and favorable pockets for migration to occur. Birders should be on the lookout for these scenarios, particularly on the weekend. By Monday and Tuesday nights, some areas of more favorable southerly winds will facilitate moderate to locally very heavy movements from the central Mississippi River Valley east across the Ohio River Valley into New England. This pattern gradually deteriorates as the work week comes to an end and low pressure spirals eastward out of the region. As this occurs, favorable conditions in advance of the pressure system spawn continuing flights, whereas northerly flow and clearing skies behind the system shut down most movements. Note the intriguing pattern in place in the latter half of the period off the Atlantic Coast, as a frontal boundary stalls off the coast (keep watching for those Red Phalaropes). The location of this boundary should be of interest to birders in New England and the Canadian Maritimes, as there may be an increased likelihood for southern migrants to overshoot their destinations.
Acadian Flycatcher. joan garvey/Macaulay Library. 22 Apr 2016. eBird S29119702
Moderate to heavy flights are likely across the region during the period when conditions permit. However, when conditions permit becomes increasingly limited from the peak extents of flights on the weekend through the middle of the work week as a frontal boundary shuts down the system. Some areas at the immediate coast will see the effects of precipitation and northerly flow in local concentrations and fallouts, especially along the Gulf Coast from the Florida Panhandle west through Texas. By Tuesday and Wednesday the frontal boundary has passed through the region sufficiently to shut down movements for all but the western and southern most extents along the Gulf Coast. Not until the end of the week does a return to southerly flow initiate moderate to very heavy flights again, albeit mostly west of the Mississippi River.
Scattered movements, running the gamut from light to very heavy, will occur locally across the region over the weekend. Low pressure moving across the region brings a range of conditions, from highly favorable to horribly unfavorable, and migrants will take flight where and when conditions allow. Similarly variable conditions persist for much of the rest of the period, though primarily varying as a function of wind speed and direction and not the presence of precipitation. If winds are lighter than expected, more extensive movements may occur as the post frontal high pressure builds into the region. By Thursday night, sufficiently widespread favorable conditions will spawn extensive moderate to very heavy flights.
Red-headed Woodpecker. Charles Shields/Macaulay Library. 28 Apr 2016. eBird S29263401
A generally unfavorable weekend for migration is in store for much of the region away from the Desert Southwest and perhaps the northern Rockies. But conditions improve dramatically on Sunday night, when widespread light to moderate flights will occur in mostly favorable winds. This pattern persists through Thursday night, with perhaps the most favorable conditions occurring in many areas on that night. Some areas, particularly in the Desert Southwest and along the eastern front of the Rockies, may experience heavy movements. Note, however, that another disturbance moves through the Pacific Northwest during the later work week, shutting down most flights in those areas.
Lark Buntings, with Pine Siskens and White-crowned Sparrow. Kathleen & Hal Robins/Macaulay Library. 8 Apr 2016. eBird S28818089
