A warm up forecast for the East brings a flood of new arrivals during the week and a chance for more fallouts along the Gulf Coast, as much of the West continues to experience typical spring arrivals. See this animation of forecast winds and precipitation for 5-12 April 2013 or below.
Light to moderate movements will occur from California through the Desert Southwest to begin the weekend, although precipitation farther north in the Pacific Northwest and Rockies will slow movements in those areas. This pattern holds through the beginning of the week, as disturbances originating in the Pacific Northwest move across the region. By Tuesday night most precipitation exits. However, movements will occur mostly in the northern portions of the region, with more southerly areas experiencing largely unfavorable northerly winds aloft that will inhibit most movements. Wednesday and Thursday see broad scale migration across the region begin and continue through the remainder of the forecast period as widespread light to moderate movements are apparent on radar. Species on the move this week include continuing passage of passerines like Pacific-slope Flycatcher, Nashville and Black-throated Gray Warblers and Black-headed Grosbeak and arrivals of Vaux’s Swift among others.
The weekend begins with stronger southerly flow across the region bringing moderate to locally heavy movements. As low pressure passes through the region, the following days see migration slow as more marginal conditions arrive in many areas including the threat of precipitation and less favorable winds, particularly northern portions of the region. However, widespread light to moderate movements will continue, with areas free of precipitation and with more southerly winds perhaps experiencing heavier movements. More southerly areas will generally experience larger movements as conditions improve farther south. Birders in Kansas and Nebraska should watch their favorite migrant traps on Monday as precipitation may fall in places where migration is underway and produce fallouts. By midweek a duality appears in the region, with unfavorable conditions to the north of Nebraska and much more favorable conditions to the south. As birds arrive in the transition zone, characterized by some strong storms, conditions may be favorable for additional fallouts of waterbirds and passerines alike. The entire disturbance moves East by Wednesday night and Thursday, unifying the region under unfavorable migration conditions that will presumably ground many birds. However, this grounding will be short-lived, as southerly flow will bring a return of more widespread moderate and locally heavy movements to end the week. Species on the move this week include Eared Grebe, Upland Sandpiper, Chimney Swift, Barn Swallow, House Wren, and Lark Sparrow.
Upper Midwest and Northeast
Although the weekend begins with northerly flow near the Atlantic Coast and generally widespread light movements, changes are afoot in the Mississippi River Valley and Great Lakes region, where more moderate movements will occur in increasingly favorable conditions. Saturday night sees a potential flood gate open for migrants in many portions of the region, as southerly flow and warmer temperatures prevail and facilitate more widespread moderate movements and some locally heavy movements. In the days that follow, through the middle of the week, marginal to favorable conditions continue in many areas of the region, facilitating daily new arrivals of spring migrants. Some areas are forecast to receive precipitation, creating conditions for fallouts. Birders should be particularly observant of the distribution of rain, checking migrant traps for early passerine movements as well as inland bodies of water for waterfowl and swallow concentrations. By the end of the forecast period, an interesting scenario is in play: a strong low pressure system moving across the region creates strong southerly flow from the eastern Caribbean north up the Atlantic seaboard. Birders should watch the progression of this front carefully, as this could create a spring overshoot situation for more typically southern species occurring farther north than expected in southeastern New York, coastal New England and the Atlantic Maritimes of Canada. Additionally, birders in the Appalachians should watch for conditions that spawn fallouts of waterfowl, early shorebird migrants, and passerines as this frontal boundary passes. Species on the move this week include Broad-winged Hawk, Laughing Gull, Caspian Tern, swallows, Palm Warbler, and Northern Parula.
Gulf Coast and Southeast
Northerly flow shuts down movement after the week’s local Gulf Coast fallouts, particularly where precipitation is still falling in the Southeast. However, the trans-Gulf system gets back on track by Saturday night and Sunday, and a new influx of arrivals will occur. Furthermore, southerly flow on Sunday night will facilitate widespread moderate to locally heavy movements across the region. The southerly flow continues through midweek, when the next disturbance moves into the region. As this system approaches the coast on Wednesday and Thursday, birders should be ready for fallouts from Texas east along the Gulf Coast to Florida depending on the speed and timing of the system’s movement. At present Wednesday afternoon and evening looks like fallout potential in Texas, Louisiana, and maybe Mississippi; Thursday afternoon has potential in the Florida Panhandle and adjacent Alabama; and Friday has potential in the Florida Keys. With southerly winds ahead of the front, movements could be moderate in areas where rain does not fall. However, it is not until late week after northerly flow has abated and return flow prevails that more extensive moderate to heavy movements begin again in Texas. Species on the move this week include Yellow-billed Cuckoo, Wood Thrush, Worm-eating Warbler and Ovenbird among other Parulids, Scarlet and Summer Tanager, Rose-breasted and Blue Grosbeaks, and Baltimore and Orchard Orioles.