Forecast and Analysis

Migration Forecast: 18 – 24 May 2012

Andrew Farnsworth The Cornell Lab May 18, 2012

While team eBird is in Alaska, our April eBirder of the month, Benjamin Van Doren, is our guest BirdCaster. Benjamin has a talent for understanding migration, developing an ambitious project to gather morning flight data from dozens birdwatchers in the Northeast that was recognized with a 5th place in the prestigious Intel Science Talent Search. Take it away, Benjamin!

Here is the coming week’s animation for the predicted weather discussed below.

Adult Western Sandpiper, Salinas, CA. Photo by Brian Sullivan.

Adult Western Sandpiper, Salinas, CA. Photo by Brian Sullivan.

Many areas of the West will experience light to moderate movements, especially the southeastern portion (New Mexico and environs), when not dealing with precipitation. Strong, far-reaching southerly flow over the Great Plains will spur moderate to heavy passage, interrupted by precipitation with potential to put down migrating birds. The Upper Midwest will also see favorable conditions punctuated by rain, as light to moderate movements continue to the east when not hampered by precipitation. Texas and some parts of the western Gulf Coast will see conditions favorable for movement, but scattered precipitation and subpar winds will slow migrants’ tracks through the Southeast, at least until late next week.

Western Sandpiper
Western Sandpiper is one of the most abundant shorebirds in North America, belonging to the assemblage of small shorebirds frequently referred to as “Peeps”. This week, Western Sandpipers will be streaming north toward their breeding grounds, many having already arrived at staging areas in Alaska. Western Sandpiper is a common migrant along the Pacific Flyway in spring and fall, but this species migrates on a broader front in fall, occurring throughout the continent and even to the East Coast. It winters along the Southeast and Gulf Coasts, stretching south to Panama and northern South America (unlike the similar Semipalmated Sandpiper, which winters mainly in South America and the Caribbean). Spring migration is more focused for Western Sandpiper, however, and the species is exceptionally rare in the Northeast at that time. Small numbers move mainly toward the northwest from wintering areas in the Southeast and Caribbean, bypassing the Northeast altogether. Indeed, finding a Western Sandpiper among the hoards of Semipalmated Sandpipers moving through the Northeast is a rare treat in spring. This week, look for Western Sandpipers along the Pacific Coast, and across the interior of the continent.

Weather Forecast
The period will begin with high pressure covering the eastern seaboard as a storm tracks from the northern plains toward Hudson Bay. This will open up a period of south winds up through the Midwest to the Great Lakes. Farther east, winds will remain light under high pressure until a weak cold front crosses the East early next week. This front will be followed by another high pressure and light winds. Across the West, the period will begin tranquil as high pressure dominates. But a storm system will come onshore in the Pacific Northwest early next week and eventually work into the Plains by the end of the week, leading to another strong period of south winds from the Gulf to the northern Plains and Great Lakes.

The absence of southerly flow across much of the west as the forecast period begins likely means an absence of widespread, substantial migration events during that time. An exception is New Mexico and parts of Colorado, Utah and Arizona, which will experience more southwesterly winds aloft and may see moderate passage. Light to moderate movements may also occur in precipitation-free areas where winds are light and variable, especially at the beginning of the week. As a storm system enters into the picture early on Tuesday and works east, areas ahead and southeast of the precipitation will experience conditions more favorable for migration–birders should watch for migrants concentrated by these rains. Northerly flow following the passage of the system will likely hamper further widespread movements through the end of the forecast period, although lighter movements (especially around New Mexico) may still occur when there are light winds and no precipitation.

Great Plains

Much of the Great Plains will experience strong southerly flow at the start of the forecast period, stretching from the Gulf Coast through Minnesota, and likely triggering heavy widespread migration events. The advance of a front bringing precipitation later in the weekend may put a damper on movements primarily near the Dakotas starting around Sunday. However, the rains may also put down migrating birds, so birders should be aware of possible concentrations of passerines and shorebirds. Far-reaching southerly flow will return fairly rapidly after the front passes, and moderate to heavy migration should resume by mid-week in most areas not affected by rains, which may again have some fallout potential.

Upper Midwest and Northeast

The forecast period begins as high pressure dominates the northeast, with conditions favorable for migration west of New York, likely spurring moderate to heavy migration events in that area. Light to moderate movements may still occur to the east, however, ahead of an advancing rain-bearing front, which will then hamper migratory passage until later in the period. Southerly winds return towards the end of the forecast period in the western part of the region, along with the potential for sizable movements. However, depending on the strength of the wind, some light movement may still occur when winds aloft are not  southerly as birds continue to surge towards their breeding grounds. These movements may occur at low altitudes, sometimes below the reach of radar, as birds seek the strata of atmosphere most advantageous for northbound flight. Fronts will bring rain to the area both early in the week and toward the end; birders especially in the Great Lakes region should be aware of possible localized fallouts as masses of migrating birds interact with advancing precipitation.

Gulf Coast and Southeast

Conditions favorable for migration will persist in Texas throughout most of the forecast period, often extending at least into Louisiana, especially over the weekend. However, unsettled weather, including scattered precipitation, may slow this influx early next week. The eastern part of the region, especially the southern Atlantic coast, will not see widespread migration-inducing weather for much of the period, thanks to a combination of northerly winds and, later, precipitation. The Gulf of Mexico will see conditions favorable for trans-gulf movement late in the forecast period, after experiencing largely easterly winds aloft-perhaps adding more of a Caribbean influence to coastal migrant traps. However, precipitation over the Caribbean, particularly late in the forecast period, may ground many late migrants hoping to set out from that region.

Posted 18 May 2012 by Benjamin Van Doren (our guest Birdcaster), Andrew Farnsworth, Brian Sullivan, Marshall Iliff, Christopher Wood of the Cornell Lab of Ornithology and David Nicosia of NOAA, on behalf of Team eBird and BirdCast.