Forecast and Analysis

Regional Migration Forecast: 12-18 April 2013

Andrew Farnsworth The Cornell Lab Apr 12, 2013

Continental Summary:

The West sees continued light to moderate movements and new arrivals in the deserts and California, while pulses of moderate and heavy movements of new trans-Gulf and circum-Gulf arrivals appear among strong passing storms. On the move this week will be Spotted Sandpiper, Chimney Swift, Wood Thrush, House Wren, Yellow Warbler, Indigo Bunting, Rose-breasted Grosbeak, and Baltimore Oriole among a diverse suite of other species.


Generally favorable conditions, with clear skies and light winds, prevail across much of the southern portion of the region for this period, whereas more northerly areas experience scattered precipitation as week disturbances pass from the Pacific Northwest toward the south and east. Light to moderate movements will be widespread in southern areas, while the early weekend and mid-to-late week periods look most favorable for light and locally moderate movements in northern areas. Waterbird and local passerine concentrations are likely in areas where rain meets nocturnal migrants, so birders from the Pacific Northwest south and east through the Central Rockies should watch their favorite migrant traps and inland bodies of water through the period. Birds on the move this week include Vaux’s Swift, Nashville, Black-throated Gray, and Wilson’s Warblers, Black-headed Grosbeak, Western Tanager, and Lazuli Bunting.

Great Plains

After a slow start Saturday night will see widespread moderate to locally heavy movements in increasingly favorable southerly flow across the region. This will include strong diurnal movements in more southern areas on Sunday, as the next frontal system begins to shut things down farther north. To begin the week low pressure and precipitation trailed by northerly and westerly winds keep birds ground for northern Plains states, while moderate movements continue farther south in continuing southerly flow. However, as the week continues, the influence of a strong low moving across the country will keep conditions largely marginal or unfavorable for movements, particularly as precipitation builds across the region and then northerly winds take hold after its passage. Movements will be locally light to moderate in areas with lower wind speeds (even if northerly or northeasterly) and clearer skies. Unfavorable conditions persist generally across the region through the end of the period. Birds on the move this week include Green Heron, Spotted Sandpiper and Hudsonian Godwit among increasing shorebird numbers, Eastern Kingbird, House Wren, Indigo Bunting, and Summer Tanager.

Upper Midwest and Northeast

A strong storm features prominently in the region’s forecast to begin the weekend, bring generally unfavorable conditions across much of the region. The storm primarily affects the Great Lakes and areas east of the Appalachians, so moderate movements will likely occur in portions of the Ohio and Mississippi River valleys behind the system. As noted in last week’s forecast, birders in coastal New England and the Canadian maritimes should be watchful for overshoot possibilities this weekend (as should birders in Bermuda!). As the system exists, strong westerly flow prevails across the region, and, though not favorable for most movements, facilitates the return of more widespread light and moderate movements. By the beginning of the week, a new low moving over the Great Lakes brings favorable conditions to much of the region, and widespread moderate and some locally heavy movements will occur from Tennessee North and East across southeastern New York and into New England. Birders in the eastern Great Lakes, Finger Lakes, and St Lawrence River valley should watch the distribution of precipitation associated with the low’s approach to the region, as more waterbird fallouts are likely to occur where southerly flow and precipitation meet. After this system passes, conditions are generally marginal to unfavorable for extensive movements for the remainder of the forecast period; the exception may be Wednesday to Thursday depending on the extent of rain associated with the southerly flow ahead of another strong low moving across the region. Birds on the move this week include Broad-winged Hawk, Chimney Swift, Red-eyed Vireo, Gray Catbird, Ovenbird, Yellow Warbler, Chipping Sparrow.

Sidebar: A Hint of Eastern Promises


Although the NAO index of late has not been terribly negative, a strong storm and associated easterly flow could bring the potential for European vagrants to Atlantic Canada and coastal New England. Birders should watch, in particular, for shorebirds like European Golden-Plover, Eurasian Oystercatcher, and others.

Gulf Coast and Southeast

After a slow start to the weekend for all but the Florida Panhandle (where moderate movements will occur), conditions will gradually improve. These improvements include return flow over the Gulf, bringing trans-Gulf migration back to the Texas coast and clearing skies and light winds, allowing moderate and some locally heavy movements to occur by Saturday and Sunday evenings. Conditions improve markedly to begin the week, and much of the region should experience moderate to heavy movements and inputs of trans-Gulf migrants. An interesting scenario to watch is the forecast for precipitation over the Gulf on Monday, potentially creating fallouts along the Alabama and Florida Panhandle coasts. Favorable conditions continue through midweek, as moderate and heavy movements become widespread across the region and increasing numbers of new migrant arrivals appear. The week ends with a strong system pushing to the Gulf Coast, bringing the next chance for a substantial fallout of trans-Gulf and circum-Gulf migrants on Thursday. Birds on the move this week include Veery and Wood Thrush, Chestnut-sided, Blackburnian, Black-throated Blue, and Tennessee Warblers, Dickcissel, Indigo and Painted Buntings, Scarlet Tanager, and Baltimore Oriole.