Graphic by John Idzikowski News from the Night Sky Radar and Songbird Migration by Kevin Kearns, Neenah, Wisconsin April 5, 2006 Nice conditions were found this evening for migrants. The next day showed this, with first reports of Hermit Thrushes from around my state, plus additional reports of Yellow Rumped Warblers and Yellow Bellied Sapsuckers from areas that had not seen them yet this year. The evening brought a little rain to Wisconsin after sunset. The winds had been blowing from the south all day after the High Pressure system moved east that had been over the Great Plains the last two nights. Coupled with a Low over the Western plains and another High over the Gulf Of Mexico, this meant nice conditions for migrants. Notice High and Low pressure combining for good migration conditions Weather Underground Notice the south wind blowing into Wisconsin. Weather Underground Radar Image There is a line that extends to the northwest from the radar in the beginning of the image. This is the radar recording the sunset. Soon after sunset, the radar begins to detect disturbances in the air. These are birds that are taking advantage of the more stable air that occurs after sunset. The surface of the earth cools, and columns of warm, rising air dissipate, resulting in less turbulence aloft. Notice that the size of the detection - "Donut" (or "Angel") - increases as time moves along. The birds closest to the radar are being detected first as they lift off and gain altitude. The radar then detects more birds as they reach altitude - typically around 1,500 ft. Due to the angle of the radar beam and its distance limit, there is a point where the detection ends. But I can look at an adjacent radar site to get an idea of what is happening throughout the entire state. National Weather Service, Green Bay Wisconsin   Copyright 1996-2006 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form