Forecast and Analysis

Regional Migration Forecast: 22-30 March 2013

Andrew Farnsworth The Cornell Lab Mar 22, 2013

Continental Summary:

This week’s migration forecast features the arrival of a strong high pressure center over the US, which will shut down migration as it approaches and builds, several disturbances that may spawn fallouts, and the potential for some European vagrants to the North and East. An animation of the forecast 925mb winds and precipitation is below.



The chances for more widespread, light migration improve across the region through midweek after a slow start, but the period ends with the threat of more widespread precipitation and grounded migrants.

The forecast period begins with generally unfavorable conditions over much of the region away from the Desert Southwest, where light migration will occur. As a disturbance moves East across the Rockies, conditions for scattered light migration improve across the region by the end of the weekend. By Tuesday night light winds will facilitate light to moderate movements in many areas. By Thursday and Friday increasing threat of precipitation in many areas may spawn some local waterfowl, swallow, and passerine fallouts in and around inland bodies of water. By week’s end only portions of the Desert Southwest will likely experience light migration as scattered precipitation shuts down migration in many other areas. On the move should be departing waterfowl and continued early arriving species like Western Kingbird, Bell’s and Warbling Vireos, Lucy’s, Yellow, and Wilson’s Warblers, Bullock’s and Hooded Orioles.

Great Plains

Mid- to late week southerly flow will bring light to moderate movements especially in the Central and Southern Plains, and birders should watch for concentrations and fallouts in some of these areas late in the period.

Generally unfavorable conditions will slow new arrivals and departures across much of the region until Tuesday, when conditions begin to improve. After low pressure exits and high pressure builds in the northern Plains, some light to moderate migration will occur across the region. As this high moves farther to the East, southerly flow will prevail over much of the Central and Southern Plains, facilitating more widespread light and moderate movements in those areas. Birders in the Dakotas and in Eastern Nebraska should watch for fallout conditions as some precipitation threat exists on Wednesday night in those areas. By late week a disturbance moves into the region bringing northerly flow in the northern Plains and southerly flow in the southern Plains. Because precipitation is also forecast with this system, and because there will be such a strong duality across the region, birders should watch their favorite bodies of water and migrant traps carefully on Thursday and Friday for fallouts and concentrations of early shorebirds, waterfowl, swallows, and passerines. In areas that do not experience rain, continued light and locally moderate movements will occur. Continued increases in early shorebirds like American Golden-Plover and Pectoral Sandpiper should be expected, as should pulses of landbirds like swallows, Brown Creeper, Ruby-crowned Kinglet, Vesper and Chipping Sparrows, and locally Smith’s Longspur.

Upper Midwest and Northeast

Unfavorable conditions inhibit most movements across the region through the entirety of the period, although a late week low pressure system moving across the Great Lakes may bring light to moderate movements from the Mississippi River valley to the Appalachians.

Unfavorable conditions will inhibit most migration for the forecast period. Low pressure moving off the Atlantic Maritimes of Canada brings northerly flow across much of the region, only to be doubled up by more northerly flow from the passage of another low pressure system moving off the mid-Atlantic states early in the week. The large high building over the Great Plains and gradually moving East will inhibit most of the arrivals to not more than scattered small numbers. By Friday high pressure moves far enough over the Southeast to bring a respite from the northerly flow to many areas west of the Appalachians all the way to the Mississippi River valley. These areas should see light to moderate movements, with some locally heavier flights, by Friday night. Though big pulses will likely not be apparent, birds on the move will include Common Loon, Wilson’s Snipe, Bonaparte’s Gull, Ruby-crowned Kinglet, Blue-gray Gnatcatcher, Pine and Black-and-white Warblers, Louisiana Waterthrush, American Tree, Chipping and Swamp Sparrows.

For those following the threads of Eastern Promises from early this year and late last year, the passage of the strong low pressure centers off the Atlantic coast highlights a period of strong northerly, northeasterly, and easterly flow across the North Atlantic. This week and next week would be good times for those in the Northeastern US and Atlantic Maritimes of Canada to watch for European vagrants, in particular early shorebird migrants and passerines. Newfoundland, in particular, is likely well-positioned for an input of vagrants.

For those watching for slingshot events of southern overshoots, the period from Sunday – Tuesday looks interesting and should be watched carefully. Conditions look favorable for early Caribbean migrants to depart from the Greater Antilles and potentially become entrained in the strong low pressure system moving off the mid-Atlantic. If this happens, some migrants could get swept into the circulation and appear farther north than typical for the season along the coast of mid-Atlantic and Northeast US.

Gulf Coast and Southeast

Precipitation brings the potential for some early season fallouts early and late in the week, but these periods are punctuated by strong high pressure that shuts down movements as it builds midweek.

Favorable conditions for trans-Gulf migration begin the weekend, but low pressure moving across the region by Saturday night and Sunday brings the possibility of northerly winds to the Texas coast, precipitation across the central and eastern Gulf coast, and fallouts in a number of places. Birders should watch the approach and passage of the front carefully, as Sunday morning and afternoon could be interesting in many areas from the Upper Texas Coast east through Florida. The forecast winds aloft suggest a higher likelihood for fallouts farther to the East in the Gulf of Mexico. As high pressure builds to the north, largely unfavorable conditions will prevail and probably limit trans-Gulf flights to a trickle and keep most overland flights to light to moderate levels through Wednesday. Western portions of the region will begin to experience more widespread moderate movements by Wednesday night and Thursday as the high moves father East, whereas eastern areas will still see much diminished movements until Thursday or Friday nights. By late week an interesting combination of strong southerly flow and forecast precipitation may make for an interesting weekend of passerine and shorebird fallouts in the Texas coastal plain and along the coast. Birds on the move this week include more raptors like Broad-winged and Swainson’s Hawks, Chimney Swift, and an array of passerines including Great Crested and Scissor-tailed Flycatchers, Yellow-throated Vireo, and Worm-eating Warbler among others.