Forecast and Analysis

Regional Migration Forecasts: 21-28 September 2012

Andrew Farnsworth The Cornell Lab Sep 20, 2012

The West is mostly tranquil, experiencing light to moderate movements over many areas in mostly light and variables. Two high pressure systems tracking East and South from Canada pass through the Central and Eastern US over the coming week and spawn heavy movements as they approach, whereas the Southeast also experiences some movements, albeit tempered by slightly less favorable conditions including coastal rain by the end of the forecast period.

Light to moderate migration will be widespread in many areas of the west through much of the weekend. This pattern continues through the middle of the coming week, but scattered precipitation will locally shut down movements in and near mountainous areas of the Four Corners Region and Nevada beginning Monday. By Thursday, a more substantial low pressure system with precipitation approaches the Pacific Northwest, likely shutting down migration in coastal areas of Washington and Oregon, and scattered precipitation in the Great Basin and Northern Rockies also will shut down movements there. Light winds over the remainder of the region, and clearer skies, will allow light to moderate movements to continue.

Great Plains
Heavy movements will occur across much of the region on Thursday night and Friday morning, continuing through the weekend in many areas. Strong northerly flow in areas East of the Mississippi River valley will probably spawn good diurnal movements, so sky watchers should be prepared for scanning the skies for raptors and other soaring birds. As high pressure builds into and then moves through the region, winds will gradually become less favorable for migration; however, clear skies and the time of year suggest that moderate movements will continue through to the beginning of the week. As the strong high continues east, southerly winds build across the region, and migration will become much lighter in most areas. Northern states will continue to see moderate and locally heavy movements, as their position relative to this strong high is sufficiently far west and north to continue to experience more favorable winds. This pattern continues to midweek, when southerly flow brings enough moist air to bring rain to the Central Plains; migration will shut down in areas of rain and will be light and scattered in light winds in rain-free areas. Rain expands across more of the Plains to end the forecast period, suggesting that migration will be light and widely scattered, but shut down by wet and warm air in many places.

Upper Midwest and Northeast
Southerly winds and increasing threat of rain through the weekend from the Ohio River valley east through New England will keep most birds grounded, and migration will be light and scattered. West of these areas, as low pressure moves into the Great Lakes, a change occurs by Saturday night. Northwesterly flow will spawn heavy movements as the low passes east, and birders in the Great Lakes should watch carefully for fallouts in areas where northerly winds and continued low visibility meet. Sunday looks to be a good day for skywatching, as stronger northwesterlies spread across the Great Lakes and Ohio River. Sunday night will see heavy and locally very heavy movements occurring from the Mississippi River east to the Atlantic in northerly and westerly winds. After this pulse, the beginning of the week is dominated by return flow from the south, as high pressure sets up shop off Long Island – migration will be light to moderate in many areas where winds are light. This pattern holds in most areas until Wednesday, with the exception of the Great Lakes where favorable winds will spawn a wave of moderate to heavy movements. Wednesday night and Thursday morning could be interesting – northerly flow associated with a high north of the Great Lakes may interact with continued rain and low visibility in the Ohio River valley area east and north through New England.  Birders should watch this scenario very carefully if it plays out as forecast, because it is a classic setup for major fallouts of migrants. Additionally, flight call enthusiasts should be out listening on Wednesday night if this pattern holds true. Once high pressure moves into the region, most areas East and North of the Appalachians will see heavy movements to end the week, whereas many areas to the west of this will see migration shut down in rain or southerly winds.

Gulf Coast and Southeast
Migration will be light to moderate in most areas to begin the weekend, with light but unfavorable or marginally favorable winds keeping movements local. Rain over Florida keeps birds grounded there. By Sunday night, more favorable winds will spawn moderate to heavy movements across the Southeast, including trans-Gulf flights. Easterly flow over the Gulf suggests that birders in Texas should watch for slightly more Caribbean flavor to their migrants on the coast, looking for Black-throated Blue Warbler and Cape May Warbler. This pattern continues to begin the week, but by Monday night light and less favorable winds begin to spread over much of the region; migration will diminish to light to moderate in most places, with the exception of Florida and coastal Georgia and South Carolina which will see heavier flights. This pattern continues through the end of the week, and in rain free areas, light to moderate movements will continue. Note that precipitation builds in many areas over the Gulf and the immediate coast, shutting down movements there. Birders in Florida and the coastal Southeast should consider seawatching during the week, as prevailing easterly flow may bring some interesting pelagics closer to shore.