Forecast and Analysis

Regional Migration Forecasts: 12-19 October 2012

Andrew Farnsworth The Cornell Lab Oct 11, 2012

As some unsettled conditions in parts of the West disrupt and inhibit otherwise light to moderate movements across the region during the coming week, an early week frontal passage through the Eastern US spawns moderate to heavy movements in its wake on Sunday and Monday nights in advance of a strong system arriving by the end of the forecast period.

Many areas of the West will see light to moderate movements in clear skies and light winds, although unsettled conditions, with scattered rain, stop most bird migration in portions of the Desert Southwest, Four Corners region, and northern Cascades. As precipitation moves out of the region, more extensive light to moderate movements occur across the region later in the weekend. However, a storm system approaching and then moving into the Pacific Northwest will spread precipitation that shuts down movements in many areas through the middle of the week. These conditions will move east, through the Great Basin and northern Rockies, shutting down movements where they occur. Any areas experiencing local precipitation that is not continuous during the night should watch for fallouts and concentrations, in passerine migrant traps and at inland bodies of water alike for landbirds and waterbirds, respectively. By Wednesday night the entire region should be nearly precipitation free, suggesting more widespread light and moderate movements may occur in many places. This week and next may represent some of the last extensive movements over the entire region, as many species are arriving or have arrived at wintering destinations.

Great Plains
A low pressure system begins to move into the region this weekend, keeping most migration light to moderate in many areas. As the system moves through the region, rain will shut down migration across a broad swath of the Plains by Saturday night. Areas ahead of this system’s passage with have unfavorable migration conditions, but areas to the west of the frontal boundary will experience much more favorable conditions. This front should appear as a dividing line between primarily light to moderate movements and much heavier movements. Sunday should be an excellent opportunity to see diurnal soaring and flapping migrants moving in stronger northerly and northwesterly winds. By Sunday night, the entire region should see moderate to heavy movements. This magnitude of movement is short-lived, as more southerly flow associated with high pressure off to the east diminishes movements through to the middle of the week. However, birders in the border states should continue to see more favorable conditions and larger moderate and even locally heavy movements. Watch, in particular, as rain moves through these areas in the middle of the week, as it may produce landbird and waterbird fallouts in the Dakotas and upper Mississippi River valley. By Wednesday night, a low tracking east toward the Great Lakes gets organized with a low move east across Manitoba, and northerly winds begin to overspread the region behind precipitation. Moderate to heavy movements will ensue in areas free of rain, with favorable conditions for nocturnal and diurnal movements on Thursday and Friday. Birders should watch this system carefully, as the low is forecast to deepen, with strong northerly and westerly winds interacting with rain, low cloud ceiling, and poor visibility in some areas; these conditions are ripe for fallouts of landbirds and waterbirds.

Upper Midwest and Northeast
High pressure over the eastern Great Lakes creates favorable conditions for moderate to heavy movements across much of the Northeast on Friday night and marginal conditions for light to moderate movements farther west over the Ohio and Mississippi River valleys and western Great Lakes. As the high tracks east off the mid-Atlantic coast and the next low moves into the Great Lakes, the region is a trichotomy for migration. New England continues to experience moderate and locally heavy movements on Saturday night, the Appalachians, lower Ohio River valley and mid-Atlantic experience light to moderate movements, and the Great Lakes see migration shut down in extensive rain. As this low and its associated wet conditions move east, conditions improve and more moderate and heavy movements spread over the region early in the week. This system divides the region, again, into widely varying intensities of movements, although Wednesday night should see primarily light with locally moderate movements in most areas. This pattern is largely the result of primarily southerly flow in advance of the next strong low pressure system forecast for the end of the forecast period. We will discuss this further next week, as this may be a significant system for depositing late fall vagrants into the Northeastern US.

Gulf Coast and Southeast
High pressure to the north on Friday night brings favorable conditions for moderate to heavy movements to the east and south of the Appalachians and marginal and unfavorable conditions to the west over the Mississippi and on into Texas. The marginal and unfavorable conditions spread east, greatly diminishing movements in most areas away from the Florida Peninsula through Monday. Variable conditions begin the week, with some areas east of the Mississippi experiencing moderate and locally heavy movements in light northerly winds. Birders in the southern Appalachians should watch closely the distribution of rain and low cloud ceiling conditions, as Monday night could be a nice opportunity to experience high flight calling in such areas. The middle of the week sees much southerly flow as high pressure builds into the eastern Gulf of Mexico, making light migration the norm in most areas. Thursday night may see significant changes in wind directions and temperatures across the region, suggesting much more widespread moderate and heavy migration will begin to spread across the western and central parts of the region that are free of rain. Portions of Texas east to the Mississippi River valley should experience good flights. Birders from the Texas Piney Woods east through the Florida Panhandle and north to the southern Appalachians should watch for precipitation and low cloud ceiling that decrease the height of many nocturnal movements and improve changes to hear mass flight calling events.