Forecast and Analysis

Migration Forecast: 11 – 17 May 2012

Andrew Farnsworth The Cornell Lab May 11, 2012

High pressure will dominate much of the country during this forecast period. The West will experience widespread light to moderate migration this week, as high pressure and warmer temperatures build in across most of the region. Moderate to heavy movements will occur in the Great Plains, despite scattered precipitation that may inhibit movements locally. Despite largely unfavorable winds aloft for much of the period, most areas of the Upper Midwest and Northeast will experience moderate to heavy movements this week; the threat of scattered precipitation will diminish movements in some locations. The Gulf Coast and Southeast should see an influx of trans-Gulf migrants in the western Gulf early in the weekend, in the eastern Gulf early next week, and generally widespread moderate to heavy movements inland, despite some periods of unfavorable winds aloft and the threat of scattered precipitation early in the period. Birders in coastal areas should watch for potential fallouts through the early portion of the week.


Warbler migration in full swing

For many birders in the East, spring migration is nearly synonymous with looking for warblers. Next week should continue to offer excitement throughout North America. Throughout much of the Great Plains, Midwest, and Northeast, this next week promises to offer some of the best warbler watching of the spring with a wide variety of species and large numbers of singing males. By contrast, migration along the Gulf Coast will have slowed,  with most migrants being females or 1st-spring birds. That said, there have been very good migration days even this late, including a fair number of rarities. While the best migration days may be past, this is still an excellent time to go birding.

The Connecticut Warbler is among the most enigmatic and highly sought warblers in North America. This species winters in South America and has a fairly narrow migration window. Even in Florida, this species is rarely noted before May (and it is very rare west of Florida along the Gulf Coast). While finding a Connecticut Warbler anywhere is always a treat, we expect a fair number of individuals to be on the move this week from Tennessee northward to Minnesota, Wisconsin, and Ohio; by late in the week birds are likely to appear in North Dakota and Ontario. This species is often best detected by song, and otherwise often remains hidden. When not signing, Connecticut Warblers are more likely to be found at isolated migrant traps, particularly in eastern North Dakota and Minnesota.

Connecticut Warbler migration map, May (all years). Note the presumed arrival in Florida after a trans-Caribbean flight from South America. Then quick movement north through the Midwest.


This period is forecast to be mostly precipitation free, and many areas of the region should see light to moderate migration. As usual, portions of the Desert Southwest and California will likely experience the most consistent and largest movements; however, many areas in which we have not typically seen much movement (until last week) should experience flights, given the extent of clear conditions across the region as a whole. Widely scattered precipitation late in the period may spawn very local fallouts; birders should watch migrant traps closely if precipitation is forecast.

Great Plains

Moderate to heavy movements will be widespread across much of the region during the period. Over the weekend and through the beginning of the week, birders in central and southerly portions of the region should watch for fallouts in areas where migrants interact with passing rain. Although some scattered light precipitation may occur locally in some portions of the region, for the remainder of the period high pressure should dominate. Winds aloft will be mostly unfavorable or marginal, but moderate and even heavy movements are still likely given the time of year. These types of movements should be more expansive late in the forecast period, as southerly flow builds into the region by Wednesday or Thursday.

Upper Midwest and Northeast

Although winds aloft are forecast to be mostly marginal during the forecast period, the fact that the region may not see substantial and extensive precipitation suggests that migration volume will be moderate in many areas, with some locally heavy movements. In areas where precipitation occurs, the potential for local fallout conditions could develop; birders across the region should watch the passage of precipitation with this in mind. This is particularly true beginning early in the week, when any checking for migrants should include both passerine traps and inland lakes.

Gulf Coast and Southeast

Many areas of this region should see moderate to heavy movements continue in areas that do not receive precipitation. To begin the period, precipitation over portions of Texas and the Gulf of Mexico may make things interesting in those areas; migrants over the Gulf that have taken off from points farther south may encounter rain, creating fallout conditions in coastal Texas and Louisiana. Birders should watch the passage of this system closely, as it may continue to spawn fallout potentials as it moves east across the region. Additionally, birders in coastal western Gulf Coast areas should watch for the potential for a more Caribbean flavor to migration, as winds aloft over the Gulf are forecast to have a substantially eastern component (particularly farther south in the western Caribbean). After passage, trans-Gulf movements will diminish to nothing for several days, with circum-Gulf migration instead in effect during this time.

Posted 11 May 2012 by Andrew Farnsworth, Christopher Wood, Marshall Iliff, and Brian Sullivan, Christopher Wood of the Cornell Lab of Ornithology and David Nicosia of NOAA, on behalf of Team eBird and BirdCast.