Forecast and Analysis

Regional Migration Forecast: 30 August – 6 September 2013

Andrew Farnsworth The Cornell Lab Aug 30, 2013

Continental Summary:

The West continues to experience light to moderate movements, as the East gets a pulse of moderate to heavy movements with the passage of high pressure through the region. Birds on the move this week will include Eastern Kingbird, Barn Swallow, Swainson’s Thrush, numerous warblers and Baltimore Oriole.


Scattered precipitation across the region during the forecast period will keep migrants grounded where it occurs, but light to moderate movements will be the norm where skies are clear. The weekend begins with reasonable conditions for such movements from the central Pacific Coast East through the Great Basin and northern Rockies, with less favorable conditions in many parts of the Desert Southwest. Saturday and Sunday nights will see the greatest extents of movements for the region during the period. This pattern continues into the work week, although increasing threat of precipitation farther north into the Great Basin and Pacific Northwest will begin to dampen movements in those areas. The end of the forecast period looks promising for more moderate movements in the Pacific Northwest, Central Coast, and portions of the Desert Southwest, while this time frame looks increasingly rainy and unfavorable for many portions of the northern Rockies as a low pressure system organizes and moves East into the Great Plains. This late week pulse in the Pacific Northwest in particular will be the highest intensity movements of the week. Birds on the move this week will include Warbling Vireo, Orange-crowned and Townsend’s Warblers, and Lincoln and White-crowned Sparrows.

Great Plains

Moderate to locally heavy movements will begin the weekend in portions of the northern Plains, diminishing slightly farther south in the region. This pattern changes over the course of the weekend, with high pressure moving into the region and associated favorable conditions for moderate to heavy movements overspreading the region by Sunday night. Sunday night will be a good night for listening to passing nocturnal migrants, and Monday will be a good time for birders to watch the morning skies for continuing nocturnal and diurnal migrants. As the high pressure center moves East, more marginal winds will blow and movements will gradually diminish in extent and intensity through the middle of the week. By Wednesday night widespread light to locally moderate movements will be the norm, with heavy movements possible only near the Canadian border where conditions will be slightly more favorable; another high pressure center passing through the Canadian Prairies is responsible for this. The end of the forecast period could be interesting, depending on the progression of low pressure and associated precipitation into the region. Forecasts call for northerly flow over the northern Plains states as low pressure moves into the Upper Mississippi River valley, but precipitation is also possible. This combination of conditions could bring about substantial concentrations of birds for the morning of Saturday 7 September if migrants take flight and encounter precipitation. Birds on the move this week will include Northern Shoveler, American Wigeon, Green-winged Teal, Black-crowned Night-Heron, Orange-crowned, Nashville, and Wilson’s Warblers, Lazuli Bunting, and Clay-colored Sparrow.

Upper Midwest and Northeast

A strong high pressure center off the mid-Atlantic coast brings mostly unfavorable winds and primarily light to locally moderate movements across the region to begin the weekend. Parts of coastal and northern New England will experience more intense movements, as these areas are far enough North of the high to experience more favorable winds circulating around the pressure center. Saturday morning may be a interesting morning to watch the skies at the immediate coast (and for those of you planning to be offshore), as conditions are favorable for birds to depart the coastline of New England and fly over water to the South and East. The disturbance that follows this high pressure system’s exit to the East will shut down movements in most areas across the region for the remainder of the weekend. As this area of disturbance passes and the work week begins, highly favorable conditions will follow and spawn moderate to heavy movements. Monday and Tuesday nights see these movements occur primarily West of the Appalachians from the western Great Lakes south through the central Mississippi River valley. Sky watchers should also visit their favorite local hawk watch sites during the day on Tuesday. Birders in the Appalachian Region and the Adirondacks should pay close attention to the weather on Tuesday night, as conditions are forecast to be favorable for concentration and fallout conditions. Wednesday will be a good day for sky watching from the western Appalachians to the Atlantic coast, and Wednesday night will see moderate to heavy movements finally spread East of the Appalachians to the Atlantic. Thursday morning will be a good morning for those East of the Appalachians to watch for morning flight from your favorite early morning lookouts. By late in the week, a ridge of high pressure building over the Appalachians and Adirondacks brings continued favorable conditions for more moderate to heavy movements from New England South and West through the mid-Atlantic states and for more morning flight on Friday morning. However, conditions farther West in the region are not favorable for much movement, with primarily light to locally moderate movements as the norm. These much less favorable conditions spread East to end the forecast period, with greatly diminished movements in evidence by Friday night. Birds on the move this week will include Osprey, Sharp-shinned Hawk, Eastern Kingbird, Barn Swallow, Veery and Wood Thrush, Philadelphia Vireo, American Redstart, Northern Parula, and Tennessee, Nashville, Black-throated Green, Magnolia, Black-throated Blue, and Bay-breasted Warblers.

Gulf Coast and Southeast

Marginal and unfavorable conditions are spread across most of the region from the weekend through the early part of the week, with light to moderate movements scattered locally around the region where precipitation is not falling and winds are calm. Not until Tuesday night does a high pressure center moving East across the Mississippi bring a major change, with moderate to heavy movements occurring on this night from western North Carolina West across the Mississippi River. As the high builds into the area, moderate to heavy movements continue on Wednesday night in many areas away from the immediate Southeast coast. To end the week, easterly flow begins to spread into the region, facilitating continued moderate and locally heavy movements from the southern Appalachians to the Sabine River; however, as this flow takes hold behind the high pressure over the mid-Atlantic, conditions deteriorate and migration amounts will be noticeably smaller in extent and intensity by Friday night. Birds on the move this week will include Mississippi Kite, Purple Martin and Barn Swallow, Nashville, Tennessee, Chestnut-sided, Magnolia, and Blackburnian Warblers, American Redstart, and Baltimore Oriole.