NEXRAD/Doppler radar question...

[killbilly]

Spent some time reading the NWS website's FAQ and looking over various radar loops and stuff...

The light blue parts of the DBz scale indicate low return, correct? In the context of weather, this indicates that there is not a great deal of moisture reflecting back from the beam as it goes across the sky?

Interpreting this in terms of VFR flight, is it then safe to assume that although there are lots of large, visible clouds up there, they aren't particularly dense in terms of the radar return, and thus unlikely to be (or become) rain clouds?

Is this correct?

 

[mikecweb]

Spent some time reading the NWS website's FAQ and looking over various radar loops and stuff...

The light blue parts of the DBz scale indicate low return, correct? In the context of weather, this indicates that there is not a great deal of moisture reflecting back from the beam as it goes across the sky?

Interpreting this in terms of VFR flight, is it then safe to assume that although there are lots of large, visible clouds up there, they aren't particularly dense in terms of the radar return, and thus unlikely to be (or become) rain clouds?

Is this correct?

I would say no that's not correct.
All that means at that particular moment there is little to no precip. In 5 mins it could be extreme precipitation.

Radar doesn't forecast. Radar has no bearing in determing if VFR conditions exist. You can have "yellow" returns on radar and still be VFR.

 

[killbilly]

I would say no that's not correct.
All that means at that particular moment there is little to no precip. In 5 mins it could be extreme precipitation.

Radar doesn't forecast. Radar has no bearing in determing if VFR conditions exist. You can have "yellow" returns on radar and still be VFR.

Right. I know it doesn't forecast, but if there is little precip, then it stands to reason that the cloud isn't particularly dense? And doesn't the density of that moisture determine whether or not the sucker's gonna open up on ya? Or am I misunderstanding/misinterpreting the picture?

I'm not arguing - just explaining the thought process and trying to learn something here. It's really interesting stuff - reading as much as I can about it.

 

[tgrayson]

And doesn't the density of that moisture determine whether or not the sucker's gonna open up on ya?

Think it's more droplet size. Raindrops require some sort of condensation nuclei to form; supposedly, ice particles are the biggest factor in the development of large raindrops, which means that the cloud must be pretty tall in the summer time. Raindrops can form through collisions, but, as I recall from my meteorology book, it's hard to get large amounts of rain that way.

 

[tgrayson]

http://www.sciencedaily.com/releases/2006/12/061209083515.htm

 

[wheelsup]

And doesn't the density of that moisture determine whether or not the sucker's gonna open up on ya?

Traditionally yes. Also take gradients into account. Sharp gradients indicate convective activity while more relaxed contours indicate more steady state rain. I'm not sure what you mean by the cloud being "dense". If you're asking if it's possible to fly VFR through the lower levels of returns, then yes, but it would depend on where the cloud layer is at. Pretty much any rain cloud is going to be solid and you wouldn't be able to climb above it.

Another thing to think about, when flying out west, the RADAR might indicate one "level" low. So a level 2 return in CO might just be a true level 3 storm.

When flying down in FL, the RADAR might indicate one level "high". So a level 3/4 return in FL might be more like a true level 2, due to excess moisture in that environment.

Just wanted to add, your best bet for determining if there will be thunderstorms are convective sigmets. They are pretty accurate.