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Radar Imagery...

I just wanted to note a first for me when it comes to the radar imagery.
I'm getting a 20 DBZ return over the island and yet there's not a cloud in the sky. The stars and the moon are shinning brightly.

The air way up at altitude is -10 degrees so I figure what I'm seeing on the radar is microscopic ice particles suspended way up there and the radar is picking it up. All the while it looks clear... I do note there's no ring around the moon and there's no dew; weird.. If it ain't ice; what then could it be? It's spreading as I write this.


Staff member
The ring around the moon is your key there. Definitely ice crystals. Pretty cool, huh? lol


Well-Known Member
I suspect what you are referring too is generically called "radar bloom" and it often happens in the evening or at night. There are several possible causes for the specific one you mentioned but the most common causes are likely biological, ie birds, bats or bugs. There are also a couple of other causes, one is called "ducting" where the radar beam is actually bent towards the ground because it's traveling through different air densities and what you are seeing is the ground reflection. Think of how a straw looks crooked when placed in a glass of water because water is denser than the air. Another is called super refraction where the range of the radar is actually extended and travels farther than normal, much like getting "skip" on the radio and you receive a transmission from much farther away than is typical.

Radar bloom happens pretty regularly in the continental US, more often in the SE but can be anywhere. The following shows birds coming out of their roosts just a bit after 8pm in the evening. Notice the ring like shape these "blooms" take on as the birds/bats take off. When I've seen bugs, they were often around rivers, lakes and streams... It's also possible that several of these causes happen together at the same time.

The ring around the moon is your key there. Definitely ice crystals. Pretty cool, huh? lol

No Tony, there was no ring around the moon so the ice crystal theory is out. I'm trying to get a screen shot of the radar because its happening again tonight.

Here in Hawaii the only migrating birds we have is the Golden Plover. Which did just return from Alaska about a month ago. But I don't think their numbers are large enough to show on radar.. Also they fly low, to low to be seen on radar. We do have some small bats, but their numbers are very low and that's why their on the endangered list.. As far as I know we don't have any kind of insect swarms. Except for them dang mosquitos..

Tonight is the same way, when the dew started to form, the radar began to clear. I think the radar is seeing simple water vapor trapped up there until the land cools. Then the air cools sinks and forms the dew. The more dew the less the radar return over the land... Just a theory of course... Oh hey, that was a great video. You can see the time zone go from east to west, cool!
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Well-Known Member
That radar image wasn't just bird migration, it also shows birds that are simply leaving/returning to their roosts as well as normal weather radar. In addition, the chance of it being insects still would need to be discounted as well as the other things I mentioned that could account for "radar bloom"

Birds or bats leaving or returning to their roosts will have a distinct ring like appearance once they are far enough away from the roost. Insects are harder to determine since they are usually just seen as a mass similar to a cloud. Insects will also be seen along streams and rivers when they aren't moving around as a group, so look along the paths the rivers/streams take and if you see something there, insects are the likely culprit. The ducting and super refraction just seem to grow outward from a radar site in the evening and then recede back in the morning.

To determine which it may be, you'd probably need to watch it over a certain time frame.
Ok more observations on these strange events...

rdsok, that must be kind of cool watching those rings form and recede back again. No chance of anything like that around here... Too much water around here, not enough range of movement. Also I noticed that the returns are forming mostly over land and dissipating over the island. They don't move away from the radar at early night and move back toward the radar again in the morning.

Also again like with the last 2 nights, the skies clear but the more dew the less radar return over the land... Never seen this before.....…. I have seen what is called sea scatter, but that looks completely different. Sea scatter is caused by high winds over the coastal waters. The winds whip up some huge waves and spray. The radar sees the wave crests and spray and it forms a ring rather close in to the radar site. Why only close in, I don't know...

Now it's after 1:00 am and the dew is drip'n. The radar is almost totally clear... WILD!! Ah?.....


Well-Known Member
Radar beams, when they aren't being ducted back down ( doesn't happen often )... are always pointed up slightly. So the farther out from the radar site, the higher the beam is from the ground/sea. An example using the lowest 0.5° tilt... at about 10 nautical miles ( nm ) out, the beam height is about 600' up in the air, at about 20 nm out, it's about 1325' up in the air. So it's unlikely that you'll see any waves or spray off of the waves unless some ducting just happens when you are looking at it.

I've been looking at the radar on Molokai last night and some tonight... What I'm seeing ( besides the clouds over the mountains ) appears to be water condensating off of the ocean. In fact, it looks very similar to insects gathering over rivers/streams in how it moves and how light of a radar return I'm seeing. Since it's weather I don't have much experience with, take that with a grain of salt.
Tonight's report..
Tonight we have clouds and light dew early on...
The radar shows the typical light easterly flow with light returns over the spine of the Koolau mountains.. This for the most part is simple geographic lift. The warm moist air blows off the ocean and when it hits land (in my case a sheer 2700 foot mountain) It rises fast condenses and boom, clouds. Without geographic lift all of Hawaii would be desert islands...

Tonight we have no rain but there's tiny droplets way up high over the Koolau's and that's what the radar is seeing tonight; I think, lol..... Also there are very small spritzers of rain passing from east to west but way out there over the water...

rdsok, I'm going to do more research on ducking or duckting or what ever... I want to better understand why the radar shows that sea surface scatter or what ever the heck it is when it's very windy. At least that what my local broadcast meteorologist says it is, ha.... For some reason I can't get a decent screen shot of the radar which brings me to a few questions...

First, is it possible for me to get a good screen shot like you did of the radar image?

Next, the Molokai radar is my main honey for obvious reasons. It's located some 3000 feet above sea level. Question: are all 88D weather radar systems set to +5 degrees (relative to the site) no matter what altitude the site is located at?

Last but not least: when do you think the new phased array system will be ready? That's going to be great!!

Thanks buddy for your time. Believe it, it's not waisted on me...………. :twothumbsup:…………….


Well-Known Member
If you are going to research it... it's "ducting" .... you won't find any "k" in that... lol

I typed 1/2 of a degree... not five degree's, can't overlook the decimal place. In general, most of the radar sites lower tilts have 0.5°, 0.9°, 1.5°, 1.8°, 2.5° and 3.5° .... I believe I read somewhere that there are about 14 different tilts, but don't hold me to it since I can't recall where I saw that. I also believe they are adding new tilts like 0.1° in there on some radar sites. I suspect only certain radar sites will get the lower tilts since ground clutter in certain areas would make it useless in some cases.

Phased array.... probably in that good question category but I don't know when it'll be ready. The last experimental version they had, still had shortcomings they are/were working around. They've recently upgraded to a newer version and I haven't heard how that is performing. They allow the public to tour the site, so when I have time, I may check it out at some point.
Oh man, it's like I said before, I learn all kinds of things on this here site. Even how to spell and are you ready for this, like you said,,, don't forget the darn decimal point; jeezo man; ha!! :dizzy:

Hey if you EVER go to the phased array site, make like a Chinese spy and snap away; LOL!!!!! :huepfenicon111:

Thanks rdsok!! ……….
Back to this? Sure why not...
rdsok, if you can, have a look at the Molokai radar, see the blue half ring just north of Molokai? Sometimes that ring goes almost all the way around the island. that's the ocean anomaly I talked about.. What is your assessment of this kind of return?? It's clear now at 1:30 am HST so it's easy to see. What the hell is that? Maybe it's flying fish,, no, n0, scratch that, LOL!


Well-Known Member
That is the radar bloom that I told you about earlier, this particular one isn't caused by biologicals ( birds, bats insects etc ). I'd suspect the ducting I mentioned earlier but I'd also ask someone trained in radar since that isn't my expertise, just an interest of mine. It looks identical to the ones I showed in the linked YT video ( minus the bio's of course that the other also included ). A quick Google search will bring you more talk about this from both experts and non-experts.
Ok thanks...…….. Yeah I want to maybe check it out with a local radar guy. Some how... There is talk about it but it's kinda,,, well,,, who the heck knows....
Have a good day...


Well-Known Member
Here is a capture of that... just a quick note, it's also on the other Hawaii radars as well to some degree...

Yeah, that's it.. I got to tell you, I like your imagery...……… Way better than the raw stuff..
And yes I noticed that anomaly on the other Hawaii radars as well... Hummmmm……….. How about this, could this be sea spray? It's been very breezy lately. Could the wind over the open ocean be throwing up enough spray with tiny salt partials? Or maybe I need to get to further research on ducting. I have to catch up on all the jobs I was doing before I blew out my back.. Very interesting for sure...


Well-Known Member
That is radar bloom... not sea spray.

Sea spray would look similar to what insect swarms would... They'd move and sway with the wind that would show when you loop the radar. In fact, the last time you had brought this up, I actually think I saw some but didn't bring it up since I'd have had to capture each of the images and combine them to show you... something I don't have software for.

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