What Am I Observing?

[MG Jennings]

While watching the radar on a couple of storms recently I have observed a circular pattern or "hole", if you will, in the interior part of the storm. It is devoid of any radar signal and does move around somewhat with each new frame.....Am I observing a well organized updraft? thanks

 

[Tim Supinie]

Are you looking at the base scan or at higher-elevation scans? Can you provide examples in images?

My first thought is that it could be a bounded weak-echo region (BWER), which shows up when the updraft is so strong that precipitation-sized particles (big enough to scatter energy from a radar beam) don't have time to form. However, this only shows up on the upper scans, and I'd need images to confirm that's what you're looking at.

 

[Greg Blumberg]

Hi MG, could you provide an image? That would significantly help us!

There are a few things that the hole could be. It could be what is called a Bounded Weak Echo Region or BWER. It could also be a radar artifact or a issue in the smoothing of the radar image (if you use that. I've seen such smoothing lead to false interpretations.)

Here's some information on the BWER, which is a part of what is called the Lemon Technique. It's a technique for diagnosing the strength of a storm from radar when the storm is in a vertically sheared environment.

http://en.wikipedia.org/wiki/Bounded_weak_echo_region
http://en.wikipedia.org/wiki/Lemon_technique
http://opwx.db.erau.edu/faculty/mullerb/Wx365/Reflectivity_severe_wx/bwer_ok.gif (The BWER can be seen in the lower left hand corner frame in this image)

 

[MG Jennings]

Thanks for the responses.....I do not have any images....I believe I was in the base reflectivity mode. To try to be more descriptive, I best describe it as an irregular hole shape with no reflectance first showing up near the front edge of the storm and as the timed images looped, it moved more towards the center of the storm. Clearly, it looked to be part of the storm structure. I am very much a beginner but it was positioned behind a large "V" shaped notch on the lower part of the storm. I have observed this on a couple of storms lately, primarily storms appearing to be a bow echo. Hope this helps.

 

[Tim Supinie]

Haha, well, I've come to the realization that in Meteorology, we name things after what they look like, not why they're significant. This causes problems when something else shows up that looks similar, but occurs for completely different reasons ("low-level jet" is another good example of this). If it's not a radar artifact or due to smoothing, as Greg mentioned, what you're seeing is technically a "bounded weak echo region" in that it's a region of weak radar echoes surrounded by a region of stronger radar echoes. But since it's near the ground, I doubt it's due to the same physics as the BWER observed in supercell thunderstorms, which is what Greg and I were both talking about.

You said it starts on the leading edge of the storm and moves towards the center. I guess this begs the question of whether or not it's stationary relative to the ground. I'm guessing not, since you believe it's part of the storm structure, but it's worth asking.

I guess the only other thing is that if you know the rough date, time, and location, you or someone else interested could go download the radar data from the NCDC NEXRAD archive (http://www.ncdc.noaa.gov/nexradinv/), plot the data, and post pictures for everyone else to view. Sorry, but there's not much more of a definitive answer we can give you without pictures.

 

[MG Jennings]

Thanks for the effort.....it might be something as simple as a clear slot of no precipitation in the storm. It was located behind the high precipitation area. In both of the recent observations, it filled back in as the storm progressed. Since I observe it from time to time, I'll get an image next time....thanks