Migration Report: 18 – 24 May 2012

Benjamin Van Doren The Cornell Lab May 25, 2012

Migration across much of the West was largely light in marginal winds aloft and scattered precipitation, although some coastal and desert areas experienced locally heavier movements. Despite a significant frontal passage that shut down movements in its wake, many areas of the Great Plains saw moderate to heavy movements. Similarly, the Upper Midwest and Northeast experienced moderate and locally heavy movements in areas free of rain associated with frontal passage. Much of the Gulf Coast and Southeast was relatively quiet, with regular moderate to heavy movements in Texas being the major exception.

Adult Mississippi Kite. Photograph by Stephen J. Pollard.

Adult Mississippi Kite. Photograph by Stephen J. Pollard.

Duality was the rule across the region, as light to moderate migration occurred primarily south of the Great Basin during this forecast period, and greatly diminished migration occurred in northern areas in scattered precipitation. Sunday night and Monday morning saw the greatest extent of movements, with light to moderate migration in evidence from Oregon and Idaho south and east through California and the Four Corners region. Some locally heavy movements also occurred during the forecast period, particularly in California. By Wednesday, a different pattern emerged, with migrants staying grounded in most areas away from Arizona, New Mexico, and parts of California. Other than scattered light movements, the period ended with little fanfare amidst scattered precipitation and largely marginal conditions.

Great Plains
Widespread moderate to heavy movements occurred across the region on Friday, with some locally very heavy movements.  However, the passage of a substantial low pressure system, beginning on Saturday, shut down migration where and when it passed. By Monday, greatly diminished movements were in evidence in the wake of frontal passage, with scattered light movements being the norm. Some areas close to the border experienced locally heavy movements, in marginally favorable conditions to the north and west of high pressure over the central Great Plains. By Wednesday, migrants were aloft in numbers again, with scattered moderate to heavy movements in Nebraska, Kansas, and Oklahoma. This magnitude of movement continued through the end of the forecast period in most of these areas, particularly along a frontal boundary establishing over Nebraska and western Kansas. More strong storms associated with this boundary, moving east through the Dakotas and into Nebraska, kept migrants grounded in these areas to end the forecast period.

Upper Midwest and Northeast
Widespread moderate to heavy movements began the period to the west of the Appalachians, whereas much more widely scattered movements, some of which were locally heavy, were apparent to the east of the mountains and north through the Adirondacks and New England. This pattern continued through the weekend, though an early week frontal boundary shut down migration in its wake. Scattered light movements were the norm as the front moved across the region on Tuesday, with scattered precipitation shutting down movements where they occurred. Farther west, the upper Mississippi River Valley saw locally heavy movements. By Wednesday, locally heavy movements in the Mississippi River Valley gradually diminished to light movements in the Appalachians; however, a substantial coastal flight occurred in New Jersey and New York. Widespread light to moderate movements ended the forecast period.

Gulf Coast and Southeast
This region experienced a generally similar pattern for much of the forecast period. Although heavy movements over Texas were widespread, most areas farther east experienced primarily scattered light movements. An exception was peninsular Florida, where some locally moderate movements also occurred. As high pressure built into the Gulf of Mexico to end the forecast period, this pattern of action over Texas and minimal movements to the east intensified. By the end of the period, the Rio Grande River Valley and central Texas continued to light up with heavy movements, whereas local and scattered light movements prevailed to the east.

Posted 25 May 2012 by Andrew Farnsworth, Brian Sullivan, Marshall Iliff, and Christopher Wood of the Cornell Lab of Ornithology and David Nicosia of NOAA, on behalf of Team eBird and BirdCast.