Topic: Understanding GRLevel3 Base Reflectivity data

[wxcrw]

We've had a boring last 24 hours, weather wise. Forecast has been partially cloudy for last night and this morning. Nothing to write home about, very scattered, and very high altitude.

I've been playing/testing GRLevel3 for my area. I've noticed base reflectivity 1 shows a ton of light blue and green cells around my area. I don't remember seeing so much activity on GR3 maps on others websites.

I've read a bunch on what base reflectivity is, what the different numbers mean, etc.. I try not to ask questions unless I've searched for the information in google, forums, FAQs, etc.. From what I have read, base reflectivity is used to show water/ice in the air. This is the main method of seeing precipitation on radar. The levels are the angle of the radar signal. 1 being closest to the ground and 5 being much higher.

If I compare BR1 maps to what I see outside, areas with 5-10 DBZ typically have light smooth clouds over them. These clouds do not look like they are producing rain, and no rain is reported on any other map I've looked at. I'm starting to question the information from NWS. Maybe GRLevel3 is too sensitive, or maybe I just don't get it.

As always, I've uploaded data to our website to share. I think it would be silly to ask others opinion on how to interpret our data without showing you the maps.

The directory where the images are currently is www.castlerockweather.org/images/GR3. I don't allow directory browsing, so you will have to include the image names. They are the standard G3Level3 names. I.E br1.jpg, br2.jpg, br3.jpg, etc..

Here is a full link to BR1:
www.castlerockweather.org/images/GR3/br1.jpg

I'll leave it up to you to change the image name to see the other images.

Thanks for your help/opinion in advance.

[jwyman]

wxcrw,
   When the weather is fair with no precip in the area, the radar site will sometimes go into what is known as CLEAR AIR MODE. They increase the sensitivity of the radar and it picks up things like birds, air with high moisture content, and even insects. This is what you may be seeing. Nothing to be alramed about. When storms, fronts, or anything with precip occurs, they will cut back on the sensitivity.... Hope this helps....

Jim

[wxcrw]

Thanks Jim. I lived in Maryland for 30 years, before moving to Colorado. I still have family near you in  Ridge, MD. I love southern Maryland. Thanks again for the comment.

[jwyman]

RIDGE! Are you kidding me? I drive there everyday for work at Webster Field, St. Inigoes... Wow, small world
BTW, I like your FTP status page.. How do you do that?

Jim

[carterlake]

Radar does not see clouds... it sees particulate matter... rain, dust, insects, geese, hail, snow, etc.

So looking out the window at clouds does nothing. Moisture in clouds will not show on radar until it forms into detectable droplets. That's the whole advantage of weather radar, it ignores the clouds and sees the rain, snow, hail, etc.

I would suggest ignoring dBz below 15 as this is generally noise. And when the radar is in clear air mode, which it is most of the time, it picks up more clutter in the lower dBz ranges.

As for GRlevel3 versus other sources... if the data is from NOAA, the images are the same... exactly the same. So "sensitivity" has really nothing to do with the images.

http://www.srh.noaa.gov/jetstream/doppler/doppler_intro.htm

http://weather.noaa.gov/radar/radinfo/radinfo.html

[neondesert]

Hi wxcrw,

As carterlake said, below 15dbz is usually not indicating precipitation.  However, reflectivity below this level is often useful for detecting things such as thunderstorm outflows.  One suggestion I have is to use a different reflectivity color table that ignores echoes below the 15dbz threshold for general precip. monitoring.  You can find a large selection of tables on this site http://www.grlevelxstuff.com in the download section.

[wxcrw]

Thanks everyone for the information. I was very impressed with the software during Sunday's thunder storms. I could track the storms from Pike's Peak, and see them steer right around Castle Rock.

I'm still testing right now, but honestly unless there is a thunderstorm rolling through i'm not very impressed with GRLevel3 software. I hate all the noise. I'm not just seeing a few spots but full maps of light blue shading. Is there a way to adjust the software to ignore DBZ below 15, and display images of only that data? Is that a trial vs full version thing?

jwyman, funny you should ask. Tonight's task is to write the scripts page for castlerockweather.org, where I hope to share all my php scripts. The first one I'll post will be the ftp upload script. Thanks for checking out my site.

[NoQuitters]

Is there a way to adjust the software to ignore DBZ below 15, and display images of only that data? Is that a trial vs full version thing?

Yes and no. First the no. There is no difference between trial and registerd versions. If you are using the default reflectivity that would explain the noise. Go here http://www.grlevelxstuff.com/index.php?categoryid=14&p13_sectionid=7 and browse through the different color tables. Pick which ones you like and save them on your hard drive as .pal files. Open GR3 and go to view, set color table, reflectivity, and change the file to one that you like with a lower DBZ.

[carterlake]

i'm not very impressed with GRLevel3 software. I hate all the noise. I'm not just seeing a few spots but full maps of light blue shading.

You mean, you're not impressed with NOAA's data... all GRLevel3 does is display it.

What you are seeing is probably related to the fact that you have mountains nearby... it's summer time... and there is a lot of dust in the air...

Those links I posted explain the issue probably better than I do.

[wxcrw]

Yes and no. First the no. There is no difference between trial and registerd versions. If you are using the default reflectivity that would explain the noise. Go here http://www.grlevelxstuff.com/index.php?categoryid=14&p13_sectionid=7 and browse through the different color tables. Pick which ones you like and save them on your hard drive as .pal files. Open GR3 and go to view, set color table, reflectivity, and change the file to one that you like with a lower DBZ.

I'm sorry guys,  I didn't understand the relationship of color table to what is displayed in the map window. I am trying A12.pal right now and it has removed all signatures below 20 DBZ. My maps now look more like what I expected and are much more usable. Thank you for taking the time to really "spell out" the whole color table process. Your post really opened my eyes to how this whole thing works. Some times you can whisper an answer, but sometimes you need to beat in into someone's head. The beating worked.

You mean, you're not impressed with NOAA's data... all GRLevel3 does is display it.

What you are seeing is probably related to the fact that you have mountains nearby... it's summer time... and there is a lot of dust in the air...

Those links I posted explain the issue probably better than I do.

Your links explained a great deal about what causes the low DBZ reading to show in GRLevel3. Information like what you posted really helped me understand exactly what I was looking at. Sometimes I forget this is a science not just technology. I'm learning. 

So last night I understood why there was low DBZ data being displayed by GRLevel3, I just didn't know what to do about it. NoQuitters's post resolved that problem. So at this point, I'm fine with the data NOAA is providing. In the future I may look elsewhere for additional data, but for testing NOAA is fine.

Once I changed the color table, I'm very pleased with this software. Once I get it down this is going to be a great resource to use to monitor weather patterns in my area.  Right now is perfect example. I'm tracking 2 thunderstorm south of Castle Rock, between us and Monument. If my web cam was mounted we could see the storm travel across the image from right to left. Ahh, we need 36 hour evenings each day.

Thanks you for the links Tom. As always you are extremely helpful and very knowledgeable.