For many people, the arrival of spring is signaled by daffodils pushing out of the ground, blossoms erupting on cherry trees, and increasingly ragged lawns.
But for meteorologists, another sign often comes to mind: the return of birds on our weather radars as our winged friends migrate northward into and across our region.
As I have described before, weather radars are quite capable of seeing targets other than precipitation. Stationary targets (like hills and mountains) are removed by clutter and terrain suppression algorithms. Birds are actually quite good targets since they are so much bigger than raindrops or snowflakes; the amount of radiation scattered by a target goes with the fifth power of its diameter, so a bird that is say 2 inches across (roughly 59 mm) scatters radar far more effectively than a raindrop (typically a few mm across).
Let's go back to Thursday evening at 6:47. Not long after sunset, there was very little visible in the Langley Hill coastal radar (you will notice a little bit of return from the ocean surface off of Hoquiam).
With dry weather the next few days, the birds should be pretty obvious in the radar imagery.