National Weather Service Nexrad Radar…It’s not just for rainy days.
True that is the primary role of the Nexrad network. Provide continuous coverage across the the lower 48 states ready to detect all types of weather and warn the public at a moments notice whenever there is danger. What to do on those dry days and nights though, the radar can still detect all sorts of phenomenon and even still serves a useful purpose for scientific research. Plus it may not be rain the radar is detecting but that does not mean you should not be concerned if your near it.
Ever see a spike on the radar like the Chicago area radar image above? Typically you would see this type of thing on a clear day with no rain yet it still shows up. It would normally be there for just one radar pass and it is not a result of the radar beam being reflected back to the site, but rather a constant stream of microwave radiation being shot at the radar beam. It is known as a sun spike and occurs whenever the radar’s sensor looks directly at the sun. This can happen at any elevation but the key is to have a clear sky with the radar’s antenna lined up perfectly. Check out a raw data radar loop and you can see the sunset/sunrise moving across the country provided the sky is clear.
More in line with the radar’s intended purpose you can still have things other than rain light up a radar’s display. Thanks to the recently upgraded dual-pol radar it is now easier to determine the shape and size of an object that returns some of the radar’s beam. This means that not only can you detect raindrops and snowflakes, but now bugs, bats, and birds are more easily seen provided there is enough of them (like a rain shower). Check out the image of the La Crosse radar. That’s not rain over the Mississippi River but rather a swarm of mayflies emerging from the water. Insects along a sea breeze can also be detected and tracked as the front moves inland along the coast.
These non weather returns are not just fun to look at but can actually be analyzed and the data used to make scientific decisions. Weather radars have tracked migrating birds and bats and that data is used to help determine the best place to site wind farms so to reduce the impact on the wildlife.