Forecast and Analysis

Regional Migration Analysis: 19-26 April 2013

Andrew Farnsworth The Cornell Lab Apr 26, 2013

Continental Summary:

Increasingly widespread light to moderate movements occurred across the West this past week, as the East experienced two pulses of light to moderate and locally heavy movements between strong frontal systems. Birds on the move included Warbling Vireo, Gray Catbird, and Yellow Warbler.



Light to moderate movements were in evidence in many areas of the region this week, particularly in California and the Desert Southwest, and even in the Pacific Northwest after an initially wet start. Several small disturbances passing through the Northwest and Rockies kept migrants grounded in areas where precipitation fell, but none of these disturbances were sufficiently large to ground large numbers of birds and halt the arrival of many migrants this week. Movements were particularly widespread and apparent after Tuesday, as a disturbance moved East mostly out of the region. Note the movements occurring in California north to the Pacific Northwest on Tuesday, Wednesday and Thursday night. This is a characteristic pattern for this time of the year, as we near a peak period of movement. Birds on the move this week included the widespread arrival of many species, highlighted by Spotted Sandpiper, Wilson’s Warbler, and Western Tanager.

Great Plains

Northerly winds and cooler than normal temperatures began the period, with little movement for Friday as high pressure dominated. As high pressure moved East, more favorable conditions prevailed and scattered light to moderate movements occurred. However, a strong frontal system moved into the region on Sunday night, shutting down migration to its North and West. In the wake of this system, migration basically shut down for the next several days as cool temperatures and northerly winds prevailed. Other than high localized light movements during this period, the only major pulse of movement occurred to end the period. A warm front brought relief from the cool and spawned moderate to locally heavy movements of birds in more easterly portions of the northern Plains, wheres light to moderate movements occurred farther south in areas away from precipitation. Birds on the move this week included Wilson’s Phalarope, Stilt Sandpiper, Chimney Swift, Brown Thrasher, and Baltimore Oriole among a suite of other species.

Upper Midwest and Northeast

A strong front just East of the Mississippi River valley spawned light to moderate movements as it advanced and shut down movements as it passed. By Saturday night, only highly localized light or light to moderate movements occurred, primarily in the western Great Lakes where slightly more favorable conditions for movements occurred. This paucity of movement was largely a result of high pressure over northern New England dominating the scene. As this high moved East, more favorable conditions slowly followed its exit across the region. By midweek, however, a new strong front worked its way toward the Appalachians, facilitating light to moderate movements in the central Appalachians but shutting down migration as it passed. Generally unfavorable conditions prevailed after this to end the period, with mostly widely scattered and local light movements in many areas. One exception was the western Great Lakes region, which was far enough from the high pressure then dominating the region’s unfavorable conditions to experience locally moderate to heavy movements in much more favorable weather for migration. Birds on the move this week included Great Crested Flycatcher, Warbling Vireo, House Wren, Gray Catbird, and many warblers such as Yellow and Black-throated Green Warblers.

Gulf Coast and Southeast

The region was bisected by a strong frontal boundary, with highly favorable conditions in advance of its approach and ¬†little to no movement in its wake. Numerous fallouts occurred along the coast as a result of the passage of the system. High pressure over the East kept migration light for most areas East of the Mississippi River and light to moderate in most areas farther west in the region through the early week. By Tuesday a new low pressure system advanced toward the region, spawning more widespread light to moderate and locally heavy movements in favorable winds. Conditions farther East continued to be dominated by high pressure and were much less favorable for much movement. As the front advanced to the Gulf Coast on Wednesday, light to moderate and even locally heavy movements occurred across much of the region. These movements included an incoming trans-Gulf flight, that departed in favorable conditions from points farther south the previous evening and encountered the frontal boundary just off the Texas coast as birds were coming ashore. This interaction (particularly with rain, strong northerly winds, and much cooler temperatures) resulted in fallouts all along the coast, the likes of which had not been experienced for 10-15 years. As the front pushed East and slowly began to deteriorate, and as high pressure built in farther north to the west of the Appalachians’ terminus, conditions to the west of the boundary generally kept most migrants grounded while favorable conditions to the east spawned moderate to heavy flights. By the end of the forecast period, the front was a disorganized boundary across the northern Gulf. High pressure so dominated the scene that most areas away from the immediate coast experienced only locally light movements. However, coastal areas along the Gulf coast in particular saw more favorable conditions, and in the western Gulf these conditions allowed some new but very late day trans-Gulf flights to arrive as the evening’s flights were departing. A special feature will appear on this system in the coming days. Birds on the move this week included Gray-cheeked Thrush, Gray Catbird, many warblers such as Chestnut-sided, Bay-breasted, Black-throated Blue, and Magnolia, Dickcissel, and Rose-breasted Grosbeak among a large diversity of other species.