For those in the greater New York City metropolitan area, the coming nights bring the return of the Tribute in Light Memorial. The powerful, side-by-side beams of light aimed skyward are first and foremost a somber tribute to the lives lost on September 11th 2001; but they also provide a rare opportunity to see nocturnal bird migration as it happens.
This year, forecast conditions are not favorable for birds to migrate en masse, and observers at and near the lights may expect to see tens to hundreds of birds in the beams at maximum. A warm, moist, and unstable air mass is sitting over the region, bring southerly and southwesterly winds aloft, the chance of isolated thunderstorms, and the possibility of fog. The following imagery depicts Convective Available Potential Energy (CAPE), one way to measure and depict the distribution and strength of turbulent updrafts and associated atmospheric energy. Values below 1000 denote a reletively stable atmosphere, whereas values greater than 3000 denote the potential for strong storms. Note the region of more intense CAPE values from Maryland North through the Southern Tier and Adirondacks forecast for evening 10 September.
In this scenario of increasingly unstable air, widely scattered light movements will be the norm across the greater New York area on the evening of 10 September. However, if winds are lighter than forecast, that slightly larger densities of birds may be on the move. In particular, the forecast winds for the middle of the night on 10-11 September are forecast to shift more westerly than originally forecast this week. If this shift occurs, even several hours after darkness, larger numbers of birds may take flight, with local moderate movements occurring during the hours in which the wind shift occurs (2-4 AM EDT).