Most of the movement in the West this period occurs this weekend and early in the week, with light to moderate movements that will see increasing arrivals of Osprey, Rufous Hummingbird, Bell’s Vireo, and Hooded Oriole. The East will experience the greatest intensity and extent of moderate movements from Monday through Thursday with increasing arrivals of Great Blue Heron, Great Egret, American Golden-Plover, Belted Kingfisher, Louisiana Waterthrush, and Song Sparrow.
Arrows show wind speed and direction (arrow points in the direction to which wind is blowing) 100 m above ground level. Areas with southerly winds are colored red; northerly winds colored blue. Accumulated precipitation (in 6 hour intervals) is green, outlined by white. Broadly speaking, areas of the map in red will experience conditions that are favorable for migration, and areas where red and green (and red and blue) intersect and overlap may experience migrant concentrations and fallouts as migrants interact with precipitation.
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A pulse of light to moderate movements from the central Mississippi River valley east through the Great Lakes and into New England kick-starts the weekend. This pulse will be short-lived for those hoping for extensive weekend movement, as unfavorable conditions diminish movements for Saturday and Sunday nights. But more favorable conditions build into the region, particularly on Tuesday and Wednesday, as southerly flow will bring more extensive moderate movements to much of the region. As the low pressure system spawning these more favorable conditions in its path advances through the region, birders should watch for local concentrations of waterbirds, early swallow movements, and sparrows where precipitation and favorable migration condition overlap. In the wake of this low pressure’s passage, migration shuts down in primarily cooler, northerly and westerly winds.
Marginal and locally favorable conditions for the first half of the forecast period will keep movements local and primarily light to moderate. Monday night sees the beginning of a more extensive favorable period, which continues nearly through the end of the period and spawns more extensive moderate movements. Of particular interest for those in western Gulf Coast and Texas is the forecast for precipitation at the end of the week. Conditions in Mexico and northern Central America are forecast to be favorable or marginally favorable for early season migrants to depart across the Gulf of Mexico, meaning fallouts are possible if these migrants encounter rain and unfavorable winds.
Migrants will be on the move in the first half of the period, increasingly and more extensively so from the weekend until a climax on Monday night. Some of these movements may be locally heavy among widespread moderate movements. But a change comes on Tuesday, as low pressure moves through the region and largely shuts down movements through the end of the period. With this low pressure passage on Tuesday, birders should watch for potential concentrations of migrants on Wednesday morning after some migrants aloft may drop out in significant rain.
Scattered light and moderate movements will be in evidence for the first part of the period, mirroring the distribution of favorable migration conditions. Most movements will, again, occur in the Desert Southwest and California. Also, note that some areas of precipitation are forecast, suggesting that concentrations of early season migrants may occur where migrants meet rain and snow. The latter half of the week sees much less favorable conditions, with the exception of Thursday night when portions of the Pacific Northwest and the northern Rockies will experience light to moderate movements.