WRAL WeatherCenter Blog

A meteorological mystery

Posted January 6, 2011 4:52 p.m. EST

Doppler - Central NC

Around lunchtime today, we observed something very interesting on the DUALDoppler5000.  We were seeing a clear scope until, seemingly out of nowhere, a "pulse" of returns appeared near Holly Springs  The returns expanded outward and dissipated over the course of about half an hour or so.

Seeing this kind of return isn't unusual in and of itself.  The DUALDoppler5000 is powerful enough to see flocks of birds, groups of bugs, and even dust under certain circumstances.  Plus, this is definitely reminiscent of what radar meteorologists (and "radar ornithologists", a very small subgroup of scientists who use weather radars to observe the migration patterns of birds) call roost rings.  However, roost rings are most typically seen at or right after sunrise: The sun comes up over the horizon, and the new sunlight causes the birds to wake up and scatter in all directions.  This is seen on the radar as a return that starts out as a point, then grows to a ring or circle before fading away.

The unusual part about this is the time of day  In the radar data, you can see little in the way of returns until about 12:45pm.  It starts as a point, grows into a blob, and continues to grow before dissipating after about 45 minutes or so.  What's more curious is that after another 15 minutes, it almost appears like the radar echoes are "returning" to the original point.  This is a departure from roost rings — when the birds scatter at sunrise, they go on about their business without all returning to the roosting point.

That said, the best theory I can come up with still revolves around birds.  A large number of them are clustered in this area near Holly Springs — a residential neighborhood behind a cluster of shops off of NC highway 55 — until, around 12:45pm this afternoon, something causes them to scatter.  After an hour or so, they begin to stream back into the original area.

If we run with this "birds theory", there are still some lingering questions:

  • What caused them all to gather in such significant numbers in this area in the first place? 
  • What caused them to scatter all at once?
  • Did they return to the original point, as the radar data would seem to suggest, or is this just an artifact in the data?

This is the best working theory we have here in the WeatherCenter, but, while I'm at a loss at what else it could be, I'm not convinced we're dealing with birds here.

Was anyone in north Holly Springs around lunchtime today?  Did you notice anything out of the ordinary?  Have another theory about what this could be?