Radar blobs & holes, what is going on?

Columbus (WCMH) – Now that it is finally raining again, several of you have noticed something on your radar and asked us about it.

Typically this is noticed at night, when the radar lights up around the radar sites, and it looks like a massive rain shower is taking over the world (or the area).

Below are two examples of this from Tuesday night, one is a snapshot of the National Weather Service US composite of radar, and the other is the single site from Wilmington, Ohio.

8-16 radar

Clearly from the image above it is not raining on 80% of the country where the radar is showing rainfall.   The majority of that area in light blue and medium blue is not getting any rainfall at all.

8-16 radar iln

On our local radar in Wilmington, Ohio, you will notice the same thing on a more local scale.   It does appear that there is a large mass of very light rain, but that is not the case.

As we head toward sunset, and temperatures begin to fall as the sun goes down, a temperature inversion can occur.

An inversion is where temperature increases with height in the atmosphere.

Inversions can cause problems for the way that a radar beam works.   To keep this less nerdy, the radar beam gets bent funny in an inversion (superrefraction in this case).

This will cause the radar to make this blob of a mess on the radar screen you look at from your app or computer.

What about the hole that is cut out in that blob?

This can be caused by 2 things.   The first is the cone of silence, or the area directly above a radar that it cannot see (or “scan”).  As the radar beam scans at different heights this hole will change in size.

The 2nd thing, and I think this was the case with some of the images you all shared via our Storm Team 4 Weather App. are below:

8-16 radar hole 1 8-16 radar hole 2

It appears the radar images above have both been cleaned up to try to make the image more friendly looking to the human eye for tracking rain.   This can be done in the software by shutting off, or hiding certain levels of the radar.

In this case it appears the lowest decibel return has been hidden a given distance from the radar site.  This is what is giving the radar a cookie cutter punch look over Southwest Ohio on the image on the left, and over Indianapolis and Northern Indiana on the image on the right.

What is interesting, you notice in both images there are slightly higher returns (higher decibel returns) are showing up inside of those circles.

We have the ability in-house to remove/hide levels on our radar as well.   This is useful when the radar appears much wetter than it actually is, we can basically de-clutter the radar a bit to give it a more real look.

If you have questions, please send them my way dmazza@wcmh.com

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