Forecast and Analysis

Regional Migration Forecasts: 28 September – 5 October

Andrew Farnsworth The Cornell Lab Sep 28, 2012

Light to moderate movements continue to be widespread in the West this forecast period, whereas periods of moderate to heavy movements in clear, fall skies are punctuated by periods of widespread rain and southerly flow.


Light to moderate migration is the norm for the region to begin the weekend. Primarily light winds and clear skies allow birds to move in many areas, with the exception of portions of the Desert Southwest and Central and Southern Rockies where precipitation may shut down movements. Similar conditions prevail for much of the forecast period, suggesting widespread and regular light to moderate movements will continue through the end of the forecast period. However, by 4-5 October a low pressure system moving ashore may bring more precipitation to a wider array of locations from central California through the northern Rockies, as well as southerly winds across much of the Desert Southwest, shutting down movements in these areas. Birders should watch their local conditions carefully as this system approaches, because boundary areas that have more favorable winds but still see low cloud ceilings and precipitation may experience fallout conditions.

Great Plains

Light and variable winds aloft will allow moderate migration in many areas, locally heavy in some central and southern Plains locations, for much of the weekend. As low pressure to the south over Texas moves east to begin the week, more northerly flow occurs in many areas; migration will be moderate to heavy in many areas as this change occurs. Birders along the front range of the Rockies should watch for low cloud ceiling conditions and light precipitation, as concentrations and fallouts may be associated with these conditions. Many areas will see heavy nocturnal migration on Monday night, and the first large waves of sparrows should appear among other later migrating passerines. Generally favorable winds continue in much of the region through Wednesday. As high pressure builds over the southern and eastern Plains states, movements will be lighter on Wednesday night. However, by the end of the forecast period, a large high pressure center over Alberta and Saskatchewan bring favorable winds and moderate to heavy movements to the northern Plains, whereas southerly flow and greatly diminished movements prevail over much of the southern Plains.

Upper Midwest and Northeast

Moderate to heavy movements will occur across the Great Lakes, Mississippi and Ohio River valleys, and western Appalachians to begin the weekend, expanding east later in the weekend as a low pressure mess moves east out to sea. Birders should watch carefully for conditions in which northerly winds prevail, but low cloud ceiling, light rain, and poor visibility also exist – these conditions bring major fallouts when they occur at this time of the year. This is shaping up to occur on Friday night and possibly other nights in the coming few days. These are especially good nights for listening, as birds may be substantially lower than normal and more vocal than normal. By Sunday, another low pressure system forming over the Great Lakes continues to bring favorable conditions for moderate and heavy movements to the Mississippi River valley, but much less favorable conditions to much of the eastern seaboard. As this next system moves east to begin the week, westerly and northerly winds again spawn moderate to heavy movements in many areas, and Tuesday morning birding in coastal locations should produce morning flights in many areas. The arrival of a new system in the northern Great Lakes by midweek divides the region, with moderate to heavy movements widespread over many western areas and primarily light or no movements in eastern areas, particularly where rain occurs. Skies clear and moderate to heavy movements prevail as this system passes on Thursday, again bringing favorable conditions for morning flight in coastal locations. However, by Friday, wet conditions may shut down movements in all but the western most areas, where light movements will occur, with some locally heavier farther North and West in the region.

Gulf Coast and Southeast

Changeable conditions, including widely scattered rain and variable winds, will keep migration light across much of the region until the beginning of the week. However, skies clear earlier in Texas and stay clear in some areas of the southern Appalachians, where migration will be much heavier. By Monday night, heavy and very heavy movements will occur over many western areas, although rain and southerly flow shuts down movements in eastern areas. This pattern intensifies through the middle of the week, as moderate to heavy movements are the norm over an increasingly large part of the region away from the southeast coastal plain. As winds aloft diminish and become more variable to end the week, movements will vary in magnitude extensively across the region; only in areas with rain will movements shut down, whereas elsewhere areas with run the gamut from light to heavy movements.