WSAW - Blogs - Jeremy Tabin

More Than Just Rain on the Radar

This week I am going to dive into what features Doppler Radar can pick up that are outside of the ordinary. Sure we make use of our weather radar to show you the movement of storms, estimates on how much rainfall occurred in a general area and of course display the velocity mode to illustrate possible rotation with a severe or tornadic storm. But did you know that we also can catch images of birds and bugs migrating across areas, or smoke from a large fire and yes even some man made structures that get in the way. In simple terms a National Weather Service Doppler Radar (aka the WSR-88D), is usually situated at about a height of 1,000 to 2,000 feet above the ground and shoots electromagnetic beams out in all directions, rotating in a clockwise motion horizontally. As those beams hit particles or objects in their path, they are reflected back to the radar where the data is collected and thus displayed on a map for all to see. Obviously in the traditional sense, the heavier the precipitation is, the higher the reflectivity level.

So what has Doppler Radar detected here in the Badger State that is not rain, hail, sleet or snow? For starters, each spring both in LaCrosse and Green Bay, we usually can catch the hatching of mayflies as they migrate away from either the Mississippi River or Lake Winnebago. In addition, you may have heard about the large fire that occurred in Cudhay on the south side of Milwaukee on Monday. This fire produced smoke, which was billowing into the sky for at least 12 hours, and during the morning hours on Monday, you could see the movement of that smoke plume toward Lake Michigan on radar.

Here's a look at the time lapsed radar image:

Meantime, later on in the year during the fall months as the birds prepare for their migration to warmer climates, Doppler Radar picks up the gathering and departure of these flocks. Of course these birds come together to rest at night and at first light, spread out to gather food from the nearby fields before beginning their journey away from the Badger State. Here's an animation of these rings of birds as they were departing their roosting areas.

On the other hand, sometimes weather radar also picks up stationary objects that extend to the same height or higher into the sky, producing false echos. A lot of times we define this as ground clutter. However over the past few years, companies working on producing alternative energy have begun to build wind farms. So far in Wisconsin, the highest concentration of these farms are in the eastern third of the state (outside of our coverage area). These wind turbines, which are clustered in groups of 20 to as many as 100, not only produce false returns on radar, but also cause the movement of the air to adjust as the wind blows through them. This in turn can make detecting severe, rotating storms more difficult in the vicinity of and down wind from the wind farms. Thus the question is, how can we continue to pursue wind energy collection, while not interfering with Doppler Radar? Well, the weather service is working on clearing up this problem on many fronts. First off, with the continuing upgrade process of the radar sites to feature dual-polarization in the next couple years, we will be better able to see things not only in the horizontal, but also in the vertical aspects of the atmosphere. In the process, the software will be updated to calculate where these wind farms are and mask them from tainting the radar data.  In addition, the weather service has put out a call to these energy entrepreneurs to consider not only the location of their wind farms in relation to National Weather Service Doppler Radar sites, but also to position their turbines in a fashion that they are not in the line of sight of the radar beam. The odds are good that there will be a continued expansion of these wind turbine farms not only in Wisconsin in the favored eastern part of the state, but in many other locales across the country in the years ahead. I'm all for clean, natural sources of making energy (solar, wind, water, etc) just so long as we're not indirectly impacting folks by creating new obstacles that produce false data and possibly put lives at risk because we weren't able to inteperate where a tornado or violent storm was moving through the area.

Here is an example of a wind farm located in eastern Dodge County, that is detected by Milwaukee's NWS Radar on a daily basis.

 

For more on this topic, check out this link to the NWS Milwaukee webpage.

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