Many non-Weather Features Visible on Radar this Morning.

This mornings radar image had a lot to look at, and most of it wasn't even weather related! 

The only precipitation on the radar was two storm complexes, one in Southern Wisconsin and another in Northern Michigan.  The rest of the circles, lines, and general clutter on the radar are all non-meteorological phenomena.


Sunrise Spikes

There are lines pointing to the northeast from the Quad Cities, IA, St. Louis, MO, and Paducah, KY radars.  These lines are called sunrise spikes and occur when the radar antenna is pointed directly at the sun.  Since the sun emits some microwave energy (same as a weather radar,) the radar receives the energy and displays it as light precipitation for the entire radial beam.  These features are only visible for a few radar scans early and late in the day when the sun is low in the sky and directly in line with the radar beam. 


In the morning, birds take off from lakes at the same time and are so numerous that they reflect the radar's energy which is interpreted as precipitation and displayed as concentric rings.  A doppler radar only displays the energy it receives and has no way to decipher whether the echoes were a result of precipitation or something else (although dual-polarization radar will allow this distinction).  These rings expand and become fainter through time as the birds disperse and the reflected energy decreases.

Wind Farms

Many nights, when the nocturnal thermal inversion sets in and causes the radar beam to superrefract, doppler radars will detect area wind farms.  Due to the density of these farms and the refractive properties of the wind turbines, they can show up as significant reflectivity which somewhat resembles heavy rain or a thunderstorm.  These "blobs" of reflectivity do not move and may vary greatly in intensity from one scan to the next.  They will typically disappear shortly after sunrise once warming allows the inversion to begin to erode although this same phenomenon can be seen anytime the radar beam superrefracts (warm layer aloft, after/during precipitation, etc...).

General Clutter

 Additional clutter across Northern Indiana and Southern Michigan was caused by second-trip echoes from the Evansville, Indiana radar.  This occurs when precipitation beyond the maximum unambiguous range is detected by a radar and plotted closer to the radar site because it took too long to return to the radar and is assumed to be data received from the following pulse.






Return to News Archive is the U.S. government's official web portal to all federal, state and local government web resources and services.