Forecast and Analysis

Migration Forecast: 20 – 26 April 2012

Andrew Farnsworth The Cornell Lab Apr 20, 2012

Areas of the western US lacking precipitation should experience widespread light to moderate migration early in the forecast period, but an increasing threat of precipitation later in the week may shut down movements in many places. The Great Plains begin the period with largely unfavorable conditions for bird movement, but by midweek southerly flow returns and widespread moderate movements should occur. A frontal passage will make for poor conditions across the Upper Midwest, but favorable conditions for moderate movements in the Northeast to begin the period. Better conditions for more widespread moderate movements should develop around midweek. The Gulf Coast and Southeast begin the period with the passage of a front that could spawn some coastal fallouts in the western Gulf region; but this front will shut down the trans-Gulf migration system until midweek, when a return to more widespread moderate movements begins.

Daily forecast maps are available here.

Black-throated Gray Warblers will be on the move in the Western US this week. Photo by Bill Schmoker.

Black-throated Gray Warblers will be on the move in the Western US this week. Photo by Bill Schmoker.

Black-throated Gray Warbler

The western U.S. should see a good movement of Black-throated Gray Warblers this week. Expect arrivals across the breeding range from Colorado to Washington, Oregon and into British Columbia. Migrants are likely to be found with flocks of Yellow-rumped Warblers, kinglets and other landbirds. Late April and the first couple days of May are also excellent times to watch for this species in the Great Lakes region, where very rare. There are several records that stretch from New York to Ohio and Wisconsin for this time period. There is even a record from St. Catherine’s Island, Georgia. Take a look at the April and May map here and zoom into your region of interest.


Light and variable winds begin the period allowing light to moderate migration to continue in many areas, particularly in the Desert Southwest, California, and in portions of the southern Great Basin. The Pacific Northwest, however, begins the period with precipitation and unfavorable conditions for much movement. These conditions continue into the early part of the week, as high pressure again builds in the Four Corners; portions of the Pacific Northwest may see some light movements depending on the extent of precipitation. Note that low pressure will be moving into the southern Canadian Rockies, creating the potential for light to moderate movements in Montana and portions of the northern Rockies; some potential for fallout exists as precipitation associated with the passage of this system may interact with bird movements, so birders should check local migrant traps on Tuesday. By midweek, more widespread light to moderate movements should occur in the Desert Southwest and southern California north and east through Montana, whereas the Pacific Northwest sees yet another storm system shutting down most movements. By the end of the forecast period, increased threats of precipitation in many areas of the West will likely shut down movements on a larger, regional scale; however, birders in the Desert Southwest should be aware of the potential for precipitation to occur in places where birds are migrating, creating the potential for some local fallouts in Arizona, New Mexico, and west Texas.

Great Plains

Northerly flow and scattered precipitation across the central and southern areas of the region will not be favorable for much movement to occur. Northern portions close to the Canadian border, however, may be far enough removed from those conditions to allow light to moderate movements to occur. These conditions continue into the beginning of the week, when some western portions of the region should begin to see more widespread light to moderate movements begin again; some areas may have heavier than expected movements given the poor conditions in the preceding days. By Tuesday and Wednesday conditions away from the border states will become increasingly favorable for nocturnal and diurnal movements, and widespread moderate migration should be apparent in much of the region. Birders should watch for diurnal movements on Wednesday in central and southern locations. Similar conditions continue through the end of the forecast period. Note, birders in some central and northern portions should watch the distribution of precipitation and northerly winds carefully on Thursday, as fallout conditions may occur at the interface of these types of conditions and bird movements.

Upper Midwest and Northeast

Although most of the Upper Midwest begins the period with unfavorable northerly winds and precipitation, many areas of the Northeast will see favorable southerly winds that facilitate widespread moderate movements. Some of these may be locally heavy. Birders in the eastern Great Lakes, far northern portions of the region, and Appalachian areas should be aware of the potential for fallouts in areas where precipitation meets bird movements. As the front passes, largely unfavorable conditions will persist across the region through the beginning of the week; some areas in the western Great Lakes may see widely scattered light to moderate movements during this time, as some clear periods with calm or favorable winds may occur. By Wednesday, with high pressure centered over the Central Appalachians, western portions of the region should see more extensive moderate movements, some of which may be locally heavy. By the end of the forecast period, many areas away from the immediate coast and northern New England should see widespread moderate movements, including scattered heavy movements; the immediate coast and adjacent areas are still forecast to have westerly and northerly winds, but even in these primarily unfavorable winds, light to moderate migration may occur and concentrate birds along the coast.  Birders in the western Great Lakes should watch precipitation associated with low pressure to the north on Thursday, as it may spawn local fallouts.

Gulf Coast and Southeast

The period begins with forecast precipitation in eastern Texas, scattered across the Southeast to the Atlantic coast, and south over the eastern Gulf of Mexico. Because precipitation over the eastern Gulf is forecast to be rather extensive, the eastern Gulf coast will not likely receive an influx of migrants this weekend.  However, if precipitation is not as extensive as forecast in migrant source areas to the south, in the Caribbean and Mexico, and birds take flight, the potential exists for fallouts in Florida and some locations along the eastern Gulf coast; birders should watch the timing and distribution of precipitation closely. Conditions will be different in the western Gulf system, and although winds are not as favorable for trans-Gulf flight, take-off appears likely from the Gulf of Campeche region; if this occurs, birders in coastal Texas and Louisiana should watch carefully for migrant fallouts along the coast. If the frontal boundary and precipitation pass as forecast, the most likely areas to receive fallouts will be more southerly portions of the coast, such as South Padre Island and Corpus Christi. The southern Appalachians and portions of the Carolinas should also see moderate movements in areas away from precipitation. As the front passes, conditions across most of the region become unfavorable for migration; the coastal Carolinas, Georgia and eastern Florida may experience moderate movements if precipitation is not as extensive as forecast and the front does not move completely through the region by Sunday. Much of the earlier portion of the week will be dominated by northerly flow across the region, and most movements will probably be light with scattered moderate movements.  Some portions of inland Texas, Louisiana, and Arkansas will see larger movements in more favorable conditions. Trans-Gulf migration will likely shut down for several days, with movements consisting of circum-Gulf migrants and more western species in the western portions of the state. By Wednesday, overland movements for both diurnal and nocturnal migrants should occur in the more western portions of the region, with nocturnal amounts of widespread moderate movements, with scattered heavy movements, diminishing farther to the east to minimal in Florida, Georgia, and the Carolinas. By Thursday, this pattern intensifies, and the return of trans-Gulf migration is likely, with widespread moderate movements overland and moderate arrival of migrants from the Gulf if forecast conditions hold.  Birders in the western Gulf should watch for a potentially eastern component to the species diversity, as easterly flow around the high pressure over Florida may facilitate the arrival of a more Caribbean flavor to migration.  Birders in the eastern Gulf may see some arrivals, although forecast winds do not like favorable for more than a light arrival.