Forecast and Analysis

Regional Migration Forecast: 2-8 August 2013

Andrew Farnsworth The Cornell Lab Aug 02, 2013

Continental Summary

The West sees light movements away from scattered precipitation over the next week, particularly along the Pacific Coast, as light to locally moderate movements associated with the passage of high pressure in the East occur primarily the northern Great Plains and portions of the Northeast. Birders should pay  attention to precipitation as it relates to shorebird concentrations and fallouts, particularly in portions of the Great Plains and Northeast.


To begin the weekend, scattered precipitation will shut down movements where it falls in the northern Rockies and portions of the Four Corners and Desert Southwest. Clearer skies and light winds in the remainder of the region, even some northerly flow along the Pacific Coast, will facilitate light and locally moderate movements. This pattern continues into the early part of the week, and light movements become more widespread as the threat of precipitation diminishes. However, by midweek, conditions become more changeable in many areas, deteriorating slightly, with a greater threat of more widely scattered precipitation and less favorable winds across parts of the northern Rockies, Great Basin, and Four Corners region. Light movements will continue in areas free of precipitation, particularly along the Pacific Coast. Birds on the move this week include Baird’s and Western Sandpipers, Red-necked Phalarope, Wilson’s, Orange-crowned, and Hermit Warblers, Lazuli Bunting, Lark Sparrow, and Lark Bunting.

Great Plains

Light to moderate movements will be apparent near the Canadian border, but precipitation farther south shuts down movements in the central and southern Plains. As high pressure builds rapidly in and precipitation diminishes, Saturday will be a good night for widespread light to moderate movements (and a good night to listen for nocturnal migrants), particularly in the eastern Plains. Conditions deteriorate to begin the week, with only scattered light movements occurring among scattered precipitation. By midweek, Border States once again see light to moderate movements, expanding farther south and east to end the forecast period. Note, however, the threat of precipitation in the southern Plains could mean shorebird concentrations in parts of Oklahoma and Kansas. Birds on the move this week include Blue-winged Teal, Semipalmated Plover, Lesser Yellowlegs, Least Sandpiper, Buff-breasted Sandpiper, Black Tern, Ruby-throated Hummingbird, Yellow Warbler, Lark Sparrow, and Orchard Oriole.

Upper Midwest and Northeast

Scattered precipitation begets a slow start to many areas of the region this weekend, with light movements occurring where it is dry. However, portions of the western Great Lakes show signs of more movements to come, with favorable conditions that facilitate light to moderate movements there early in the weekend building South and East to begin the week. However, as high pressure moves off the Carolina coast, precipitation returns to shut down migrants in most places, again with the exception of portions of the western Great Lakes where light movements continue. This precipitation is tracking a low moving East across Canada, and as it departs more northerly flow builds over parts of the region. As this happen late in the week, more favorable conditions are in place for light to moderate movements to occur in areas free of precipitation. Birds on the move this week include Blue-winged Teal, early Ospreys, Semipalmated and Black-bellied Plovers, Solitary, White-rumped, and Pectoral Sandpiper, Yellow Warbler, and American Redstart.

Gulf Coast and Southeast

Generally unfavorable conditions prevail across the region for the first few days of the forecast period, although light movements will occur in areas with light or calm winds away from precipitation. Monday night is the first night with a chance for more moderate movements scattered among the light movements, as marginal to slightly favorable winds occur as high pressure moves toward the Carolina coast. However, these conditions are short-lived, as more precipitation spreads across many areas of the region for the remainder of the week, shutting down most movements. Light to moderate movements may reappear over Texas to end the forecast period, depending on the extent of rain and whether forecast northerly flow materializes there. Birds on the move this week include Blue-winged Teal, Swallow-tailed Kite, Semipalmated Plover, Solitary, Upland, and Buff-breasted Sandpipers, Ruddy Turnstone, Wilson’s Phalarope, Louisiana Waterthrush, and Black-throated Green, Cerulean, and Yellow Warblers.

Additional Comments

For those watching the radar in your respective regions, remember to review velocity images for your local radars with an eye on wind speeds aloft to clarify bird, insect and bat movements; large numbers of insects and bats will be flying or drifting at night where and when precipitation is not falling in most mid-to-late summer periods . Please see this paper by Gauthreaux and Belser (1998) and this paper by Diehl and Larkin (2002) for additional information on resolving (or attempting to resolve) birds and other biological targets on radar imagery.