Forecast and Analysis

Regional Migration Forecast: 12-18 May 2013

Andrew Farnsworth The Cornell Lab May 10, 2013


Continued light to moderate movements are again the norm for the West away from areas of precipitation, as the East waits to experience moderate to heavy movements in many areas until the middle of the week. Birds on the move this week will include Willow Flycatcher, Swainson’s Thrush, Magnolia, Canada, Wilson’s, Blackpoll, and Bay-breasted Warblers, Scarlet Tanager, and Baltimore Oriole.


The weekend begins with scattered precipitation in the Rockies and Desert Southwest that will stop movements where it occurs, while light to moderate movements continue along the Pacific and in areas that are precipitation free. Conditions deteriorate, however, in the Pacific Northwest to begin the week, as light to moderate movements persist in most other parts of the region away from the more extensive precipitation. This pattern continues through to midweek, by which time most of the precipitation moves East out of the region and light to moderate movements expand, particularly in the Desert Southwest and southern California. The end of the week sees mostly favorable conditions continue for light to moderate movements, but increasing chances for scattered precipitation will likely shut down movements in the Desert Southwest and Cascades. Birds on the move this week will include far northern shorebird and alcid arrivals, Olive-sided Flycatcher, Swainson’s Thrush, Yellow and MacGillivray’s Warblers, Black-headed Grosbeak, Lazuli Bunting, and Western Tanager.

Great Plains

Passing low pressure to the east and north bring largely unfavorable and unseasonably cool conditions to the region for the weekend. Areas in which winds are light may see locally light to moderate movements, but these will be scattered and primarily farther south in the Plains. Conditions slowly begin to improve as high pressure builds and moves East across the region, and moderate to heavy movements will follow on Sunday and Monday nights, particularly over Nebraska and the Dakotas. Tuesday will be an interesting day, with northern areas experiencing light to moderate movements under the effects of a low over the Canadian Prairies and southern areas having highly favorable conditions for heavy movements. Although no precipitation is forecast in the areas where wind shift occurs over the Dakotas, birders should be outside listening for the effects of the wind shift on nocturnal migrants and watch for local concentrations on Wednesday morning. Unfavorable conditions associated with the low pressure center overspread the region by Thursday, shutting down most movements. For the remainder of the period, increasing threats for precipitation and light winds will make for complex nocturnal movements, as moderate to heavy movements will occur in precipitation free areas with light winds and fallouts and local concentrations may occur where precipitation falls. Birds on the move this week will include Black Tern, Willow Flycatchers and early Alder Flycatchers, many warblers including Mourning, Magnolia, and Blackburnian, and Orchard Oriole.

Upper Midwest and Northeast

A substantial low pressure system arrives in time to shut down early weekend movements in the Appalachians and in its wake across the Mississippi River valley. However, the coastal plain from Virginia North and East through southern New England should see the favorable conditions continue, spawning moderate to heavy movements in many of these areas. Birders in these areas should watch the distribution of precipitation carefully, as local concentrations and fallouts are likely as precipitation spreads East with the approaching low. Additionally, birders should be listening for nocturnal migrants, as overcast skies and artificial lighting around urban areas will create an audible chorus in places where birds are moving. Furthermore, birders should continue to monitor inland lakes, as this system has already produced interesting waterbird fallouts father south in the region. As this low passes, precipitation spreads across much of New England by Saturday night, but some areas are still forecast to have southerly and southwesterly flow. If this happens, and rain is not present, continued moderate to heavy movements are likely. A note – those in New England and the Canadian Maritimes should watch for potential overshoot migrants in the strong southerly and southwesterly flow forecast during this system’s passage. Behind the frontal passage, conditions will be marginal for movements at best, with northerly and northwesterly flow and cool temperatures. Light to moderate movements may occur despite the conditions, if winds are light, given the time of year. Marginal conditions like this continue through to Monday night, when the next pulse of southerly flow arrives in the Mississippi River valley and spawns moderate to heavy movements there. These conditions spread East by midweek, and moderate to heavy movements should occur in many areas on Wednesday night. As these conditions spread East, the threat of precipitation increases so birders should once again be mindful for local concentrations and fallouts where rain falls. Low pressure associated with this precipitation organizes and moves East to end the week, and the complex conditions it brings to the region will spawn moderate to heavy movements in New England and shut down most movements from the eastern Great Lakes through the Appalachians and Ohio River valley. The end of the week looks good for waterbird fallouts, so birders should check inland bodies of water in Ohio, New York, and Pennsylvania on Friday 17 May. Birds on the move this week will include Eastern Wood-Pewee, Willow Flycatcher, Swainson’s Thrush, Cedar Waxwing, numerous warblers including Bay-breasted, Wilson’s, Magnolia, Canada, Blackpoll, and Mourning, Indigo Bunting, Scarlet Tanager, and Baltimore Oriole.

Gulf Coast and Southeast

A frontal boundary is again approaching the Gulf Coast, and with favorable exodus conditions forecast on Friday and Saturday nights in northern Central America, fallouts are likely on the Gulf Coast. The timing of the system’s arrival will determine the extent of these fallouts, but conditions look favorable for a 1-2 day event in many areas of the Gulf Coast West of the Florida Panhandle. By the end of the weekend and the beginning of the week, the front pushes far enough south that trans-Gulf movements shut down, and moderate to locally heavy movements of birds occur in light winds over land behind the frontal boundary. However, the Florida Peninsula will then become the focus of migrant – precipitation interactions, and fallouts are likely to end the weekend and begin the week. As high pressure builds into the region, moderate to heavy movements follow over portions of Texas free of precipitation, while the rest of the Southeast sees only locally light to moderate movements. Note that trans-Gulf conditions do not return to favorable for the entire week, which means many migrant arrivals may be later than expected and birds may concentrate because of light winds and greater exhaustion. Conditions gradually improve for more widespread moderate to heavy over land movements over the course of the week until Thursday. However, the end of the week sees more instability, and complex conditions will see heavy movements in some areas and total shut downs in others. Birds on the move this week will include White-rumped Sandpiper, Yellow-billed Cuckoo, Yellow-bellied, Willow, and Alder Flycatchers, and Mourning and Canada Warblers.