Forecast and Analysis

Regional Migration Forecasts: 14-21 September 2012

Andrew Farnsworth The Cornell Lab Sep 14, 2012

Several nights of heavy movements are likely in the central and eastern US over the coming week, whereas the West will experience primarily moderate movements in light winds and generally dry conditions. This week’s regional forecasts follow:

Widespread light to moderate migration is likely in many areas of the West for the coming week. Rain is a non-issue, other than perhaps in the Four Corner region late in the forecast period, and light winds, even westerly and northerly winds, should be favorable for birds to move. Birders in coastal areas should watch closely for nights with easterly components to winds, as the following morning’s birding in coastal stopover habitat should have migrant concentrations. Also, birders considering a trip to Baja California in the coming days should take note that northerly winds are forecast for early in the week – concentrations of birds in oases and habitat patches should yield migrants and vagrants.

Great Plains
Light to moderate migration will be widespread across the region. High pressure will bring light southerly flow and clear skies to most areas. By the end of the weekend, a change begins, with more northern areas seeing a wind shift and much heavier migration and more southern areas seeing a shut down in migration because of warm and moist air from the Gulf. By Monday night, an approaching frontal boundary will spawn heavy migration across much of the region.  Birders in the eastern Plains should watch carefully for fallouts, as northerly winds facilitating these large movements may interact with precipitation in some areas. As the week continues, conditions become briefly more marginal, with migration becoming moderate in most areas, locally heavy in places with light winds, before high pressure again builds in from the western. As this high pressure arrives, heavy and very heavy movements will be the norm in many areas. Additionally, birders should plan to visit their favorite sky watching haunts on Wednesday, Thursday and Friday – hawk movements and day-flying migrants should be apparent in many places. Birders in the southern Plains should also watch for fallouts at the end of the forecast period, depending on the extent of rain and where it meets northerly winds.

Upper Midwest and Northeast
Building high pressure will begin to spawn heavy movements across the Great Lakes and Northeast over the course of the weekend. By Saturday night, heavy and locally very heavy movements will occur over much of the region, from the Ohio River valley through New England. Coastal interests should watch for morning flights to occur along barrier beaches and leading topographic lines. Sky watchers should be ready for nice raptor and diurnal migrant flights on Sunday, and birders should check their favorite patches on Sunday and Monday mornings. As this high pressure settles over the mid-Atlantic, and moves east, more southerly flow begins to diminish migration in most areas; additionally, rain shuts down movements over the northern Appalachians and DelMarVa. Midweek looks like a wet mess across most of the region, with migration shut down by precipitation and warm, moist air in many areas.  However, the next cold front already has a foot in the region, and Tuesday night and Wednesday will see heavy movements in portions of the western Great Lakes and upper Mississippi River valley. Although the front passes by Wednesday night, high pressure the south does not bring much of a wind shift or drying effect. However, migration over much of the region will be moderate in clear skies where light winds occur. The end of the forecast period looks marginal at best for most movements, as a strong low pressure system in northern Ontario brings instability to the atmosphere for much of the region.

Gulf Coast and Southeast
Circum-gulf migration is the word this weekend, with moderate to heavy migration occurring in Northeasterly winds over many areas of the region free of rain. As high pressure moves east, warm and moist air shuts down most movements over Texas and portions of the Gulf Coast to begin the week. This pattern intensified for the early part of the week, with only the western and central portions of Texas experiencing semi-favorable migration conditions and primarily moderate movements. By late Tuesday and Wednesday, more favorable conditions return after frontal passage, and many areas of the region from Texas to the central and southern Appalachians experience moderate to heavy movements. The coastal plain in the eastern Gulf states and the Atlantic will see rain shut down most movements. As high pressure once again builds into the region to end the forecast period, conditions become much less favorable for migration – moderate movements will be local across the region in areas without rain and with light winds.