As you may or may not know, weather RADAR (RAdio Detection And Ranging) has been in use for decades to detect precipitation in all forms, from rainfall to snow to hail.  These targets are known as non-biological targets.  In addition to precipitation, radar is used to monitor aircraft on a regular basis.  But did you know that the radar "sees" other objects in the sky as well? 

Radar operates by sending out a narrow beam of electromagnetic energy into the atmosphere as it rotates.  Some of that energy bounces back off precipitation and is captured by the radar dish as a "return echo".  Those echoes are then processed by a computer and plotted on the radar map which you can access through many sources including TV and Internet.  Although the radar is "tuned" to see objects about the size of rain drops and snow flakes, it also receives reflected energy from other sources ranging from dust particles, smoke and cloud droplets on the small side to insects and birds on the large side.  The FAA has radars that are tuned to look at even bigger objects such as aircraft.

Fig 1:  WSR-88D Mosaic Radar Image 8/16/11 1034z at 0.5 degree elevation showing several bird rings across the Lower Great Lakes.

This time of the year some really weird patterns begin to appear on the weather radar.  One of those patterns is a series of rings that appear right around sunrise for just a few minutes on certain days.  If you look at a mosaic of weather radars, you may see several of these "rings" on any given day (Fig.1 ).  What are they?  Well, they're actually birds, hence the reference to "Fowl" weather in the headline. 
Beginning in late June and July, after most birds have completed the breeding season, they begin to assemble in large groups at roosting sites.  These groups of birds can sometimes number in the thousands.  Each morning, right around sunrise, the birds begin to leave the roosting site for the day to feed.  As they rise into the sky and head out in all directions, they pass through the radar beam and reflect a bit of energy back to the radar.  Since they all leave around the same time and head in all directions, they form a ring as they move away from the roosting site, hence the rings that appear on the radar. 
If you click on Figure 2, you will load an animated gif (warning, it's 3mb in size) that will provide a loop of the development of several bird rings that occurred on a recent morning across the Lower Great Lakes Region.  You can follow the development of the rings, beginning in the east and expanding westward as the sun rises across the landscape. As noted, when the birds leave their roost, the bird rings expand.   Most of the rings occur along the shoreline of the Great Lakes where there are several State, Provincial or National Wildlife refuges.


Fig. 2:  WSR-88D animation showing the evolution of the bird rings across the Lower Great lakes Region on 8/11/11.

In Figure 3, I have identified the locations of nearly a dozen of those bird rings which, not too surprisingly, are associated with popular bird watching spots and known locations for roosting sites.  These include but are not limited to:


Fig 3:  Locations of several bird rings detected on the WSR-88D.

  1. Cape Vincent at the head of the St. Lawrence River
  2. Montezuma National Wildlife Refuge in The Finger Lakes Region of New York
  3. The Iroquois National Wildlife Refuge in Western New York
  4. Presqu'ile Point on the north shore of Lake Ontario, Ontario Canada
  5. Selkirk Provincial Park near Port Dover on the north shore of Lake Erie Ontario Canada
  6. Long Point Ontario on the north shore of Lake Erie
  7. Presque Isle on south shore of Lake Erie near Erie PA
  8. Near Fairport Harbor on south shore of Lake Erie
  9. Pt. Mouillee State Game Area MI at west end of Lake Erie
  10. East shore of Lake St. Clair, Ontario Canada
  11. East shore of Saginaw Bay on Lake Huron.              
In summary, the weather radar's main role is to help the meteorologist analyze and diagnose the atmosphere for precipitation.  That analysis covers everything from precipitation type to intensity to severe weather characteristics for thunderstorms and tornadoes.  However, it also gives us a look at other features in the atmosphere that you may not have been aware of.  Before leaving, I will bet some of you were wondering about those curious "spikes" that occur from each radar for a scan or two in the animation you saw.  That is the radar detecting the electromagnetic energy from the sun as it rise above the horizon.  We will talk more about that in a future article, stay tuned !!