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Author Topic: Dual Polarization Radar Guide  (Read 30291 times)

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Offline storm_chaser

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Re: Dual Polarization Radar Guide
« Reply #15 on: October 13, 2012, 12:56:00 PM »
Thank you very much indeed Kevin. I would like to pay my respects. Your explanations was very useful for me. Turkey is just getting strated to use Dula pole  radars and if you permit I want to ask some questions when I see problems about dual pole.
Now I am looking other forum subjects and like it your forum too much. I will try to contribute to the forum next days.

Offline Adam

Re: Dual Polarization Radar Guide
« Reply #16 on: December 28, 2012, 08:37:30 PM »
Alright Kevin would this be all snow West of Memphis here? And great posts you have here. Wow! :)
AND A LOT CAN CHANGE BETWEEN NOW AND THEN.

Memphis Weather

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Re: Dual Polarization Radar Guide
« Reply #17 on: December 28, 2012, 09:00:49 PM »
Thanks Adam  :)

What I see there on CC tells me one primary thing: All the hydrometeors (precipitation targets) are nearly uniform. That means mixing is not likely. So...its probably all rain or all snow.

However...you have to consult other products to come to a reasonable conclusion. First, check ZDR. Corresponding to your image...I saw ZDRs generally quite low except on the fringes of precipitation. Low ZDR (less than one but optimally near zero) usually means snow.

Still, need to check something else. The melting layer. In this image...the beginning of the melting layer was just W of the MS River...or about 2,000 ft up on the radar beam. All the precipitation was BEHIND the melting layer...which means yes CC/ZDR can confirm snow...but that MAY not be representative of surface conditions. We at least know to about 2,000 feet its snowing.

Now, check your METARs. Surface temp of 32 at Walnut Ridge, 32 at Newport, and 34 at Jonesboro. Final conclusion on that precip area tells me its snowing there with very good confidence. However, West Memphis is showing 36 which means chances are less it would be snowing there. Don't have any reports during that initial band over Wynne/Harrisburg...so this is where you have to outright guess. Mine: Probably rain, but I won't rule out some mixing in that lowest 2,000 feet and perhaps even all light snow.

So, as you can see...there are still some drawbacks and limitations to the data. But, with dual-pol added we could have some increased confidence overall and better data to make educated guesses with.

Offline Adam

Re: Dual Polarization Radar Guide
« Reply #18 on: December 28, 2012, 09:03:17 PM »
Wow this is very interesting to me. I will have this book marked from now on. Thank you kevin.
AND A LOT CAN CHANGE BETWEEN NOW AND THEN.

Memphis Weather

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Re: Dual Polarization Radar Guide
« Reply #19 on: December 28, 2012, 09:08:21 PM »
Wow this is very interesting to me. I will have this book marked from now on. Thank you kevin.

Absolutely. As you can see there's no simple way to figure everything out but as we get access to more and more of the dp data...already learning more of the positives and negatives to it.

Offline Adam

Re: Dual Polarization Radar Guide
« Reply #20 on: December 28, 2012, 09:09:07 PM »
Another picture. What is the strange line going towards Nashville.
AND A LOT CAN CHANGE BETWEEN NOW AND THEN.

Memphis Weather

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Re: Dual Polarization Radar Guide
« Reply #21 on: December 28, 2012, 09:12:57 PM »
Another picture. What is the strange line going towards Nashville.


Two options there: Either big rain drops or melting snow/graupel. Because this is on the edge of the melting layer...this is likely melting winter precip as it gets into the lower radar range. A look at CC in that area will confirm lower values...which means multiple target types (in this case: melting).

EDIT...to be fair...this could be case where both are happening. Winter precip melting aloft but surface conditions represent moderate rain with big drops.

Offline Adam

Re: Dual Polarization Radar Guide
« Reply #22 on: December 28, 2012, 09:18:14 PM »
Nice this seems really neat. A weather person in my county has told me about it. His name is Ben Luna he works at 31 in Huntsville Tennessee. He thinks it is useful, but does not like the idea of the radar having to split power between vertical and horizontal beams. He does not think the radar is as strong than a normal nexrad. Being in Lawrence County so far from Nashville's radar this is a concern. Is this true?
AND A LOT CAN CHANGE BETWEEN NOW AND THEN.

Memphis Weather

  • Guest
Re: Dual Polarization Radar Guide
« Reply #23 on: December 28, 2012, 09:23:04 PM »
Nice this seems really neat. A weather person in my county has told me about it. His name is Ben Luna he works at 31 in Huntsville Tennessee. He thinks it is useful, but does not like the idea of the radar having to split power between vertical and horizontal beams. He does not think the radar is as strong than a normal nexrad. Being in Lawrence County so far from Nashville's radar this is a concern. Is this true?

Not true by in large. The NWS presentations went through this...showing that while there is weak power loss...at most you're only losing the lightest of precipitation echoes. Furthermore...if you have a 65 dbZ echo in single pol...it's still going to show up as 65 dbZ in dual pol do you're losing anything in that way either.

Offline Adam

Re: Dual Polarization Radar Guide
« Reply #24 on: December 28, 2012, 09:24:57 PM »
Not true by in large. The NWS presentations went through this...showing that while there is weak power loss...at most you're only losing the lightest of precipitation echoes. Furthermore...if you have a 65 dbZ echo in single pol...it's still going to show up as 65 dbZ in dual pol do you're losing anything in that way either.
Okay thank you for clearing that up. I will tell him about that. You are very imformative about this Kevin and it is very interesting.
AND A LOT CAN CHANGE BETWEEN NOW AND THEN.

 

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