View Full Version : Weather Radar interpretation

John Citizen
16th Mar 2011, 12:04
How do you determine if a heavy/red radar return is :
- heavy stratus rain (meaning it safe to fly through)
- thunderstorm / CB cloud (not wise to fly through)

Sometimes the return will be solid red but you know it is only heavy rain so you continue to fly through it.

Other times it might be a CB :eek:

How did you tell the difference. :confused:

16th Mar 2011, 12:53
Try reducing the manual Gain control (if fitted) to minimum setting (as against Auto/Cal/ or max). If the picture is still strongly red then avoid like a plague. This technique was usually successful when operating into Pacific islands where very heavy rain associated with towering Cu would cover the radar screen with red returns. By experiementing with the Gain control you could eliminate most of the heavy returns and the last one left was the one to avoid as it may be a CB rather than a towering Cu.

Same principle for high altitude cruise with certain types of radar. In this case set the Gain out of the automatic position into the MAX gain and the tops of CB normally invisible in AUTO gain, would show up as a very small echo. But enough to arouse suspicion that something big is in front. Tops of big CB up to 50,000 ft are usually dry and thus no reflection but with MAX gain often something shows up as a tiny return.

Get a copy of the radar manufacturer's Pilot Information Manual. Always good information in it.

Dream Land
16th Mar 2011, 12:58
How do you determine if a heavy/red radar return is :Years of flight experience helps, the RED color alone is no guarantee that dangerous weather exists, there are so many other factors, like shape and geographic area.

Cheers, D.L.

Green Guard
16th Mar 2011, 23:09

By experiementing with the Gain control you could eliminate most of the heavy returns and the last one left was the one to avoid as it may be a CB rather than a towering Cu.

By experimenting i.e reducing the gain, you may find yourself in the middle of the 5hit very easy.:}

If you were "experimenting" i.e. moving your radar beam up and down, as necessary, using Tilt, you would be in a much better situation.

17th Mar 2011, 00:17
john citizen

invest in an archie trammel radar course or video...great stuff. play around with tilt and gain ALOT!

some radars have a magenta tone in the red and that can be really bad.

I've learned that it is the boundry between colors that can really smack you upside the head.

17th Mar 2011, 00:49
Unfortunately, much of what you read here on PPrune is utter nonsense. I strongly suggest you have a look at the Airbus documents....two in particular....one is Getting to Grips with Aircraft Surveilance, the other is Optimum Use of the Weather RADAR.

This is a start......

Next, discuss this issue with someone in your training department.

Asking the opinion of an experienced captain may be f benefit, as well.

Fly safe,


17th Mar 2011, 01:32
john citizen

my airline issued us the archie trammel course and everyone loved it.

certainly read what your airline gives you. but you have just heard it from an experienced airline captain...

come on pantload

17th Mar 2011, 03:29
Check your pms'.

17th Mar 2011, 12:31
How do you determine if a heavy/red radar return is :
- heavy stratus rain (meaning it safe to fly through)
- thunderstorm / CB cloud (not wise to fly through)

It's a combination of the latitude you are flying at, and the radar height of the cloud you are studying. The radar is calibrated for temperate zone weather - so gives a falsely strong reading in tropical zones, and a falsely weak reading in desert zones. Calibrated gain adjustments can correct for this if you know what you are doing! Determining the radar height of the cloud is part of the picture as well.

There are plenty of threads here on it (including Archie Trammel's info):





etc etc

18th Mar 2011, 14:07
Asking the opinion of an experienced captain may be f benefit, as well.

I think you will find quite a few Pprune contributors are (or used to be) experienced pilots. You don't have to be a captain to be an experienced pilot.

18th Mar 2011, 14:15
For my benefit, what is "heavy stratus rain", JC?

John Citizen
22nd Mar 2011, 15:03
what is "heavy stratus rain", JC

It should not be too hard for an intelligent person to work out what it is if you know the meaning of each of the individual words :
1. Heavy
2. Stratus
3. Rain

You can find many references to "Stratus Rain" in this Honeywell document if you still can't work it out

Airborne Weather Radar Interpretation (http://www.scribd.com/doc/44837140/Airborne-Weather-Radar-Interpretation)

22nd Mar 2011, 16:00
JC - as A37575 stated, decrease sensitivity at low altitude, increase sensitivity(gain) at high altitude. Newer aircraft can reduce gain below the old 'auto/calibrated/normal' setting.

Tilt is inverse to altitude. Low alt = tilt up, high alt = tilt down.

Rapid increase in intensity is not good.

Practice(gain/tilt) with storms you can see as you manuever past them. Use that knowledge(experience) at night or when you're in clouds (IMC) and can't see the storms.

Not a fan of the official guidance in the AFM's re: radar use. Air France President spoke about another flight (AF?) hitting turbulence at altitude along the same route as AF447. Said the Captain switched to a more sensitive setting (that is not AFM guidance..) and changed his route of flight based on the new radar depiction.

After all this there is no guarantee about weather you're penetrating. Sometimes it's better, and sometime it's worse, than you'd expect.

22nd Mar 2011, 18:03
JC - I'm sure that is a fantastic book you have linked, but here is the definition of 'Stratus' cloud/rain for you. You do not get 'heavy rain' from Stratus cloud as you can see, hence my query

"Stratus clouds are more known for drizzle than for precipitation, however. When heavier rain falls from them, their title is changed to nimbostratus clouds

Nimbostratus clouds form at or below 6,000 feet. They are dark, low level clouds that bring light to moderately heavy prolonged precipitation, such as snow or rain.

Altostratus clouds are incapable of producing heavy precipitation, but they are often the cause of a light drizzle. Following altostratus clouds are nimbostratus clouds, which are the source of heavier precipitation."

I believe '"Nimbus" is 'Rain cloud' in Latin. Hope this helps!

23rd Mar 2011, 01:37
jeezus JC...

If you have questions about "heavy/red radar return", do you expect everyone to know which system you are using?

Aside from that.....

You would ask the question on a forum ( and F with the people that respond) rather than your chain of command?It should not be too hard for an intelligent person to work out what it is if you know the meaning of each of the individual words :

Yet ..YOU..as an intelligent person, can find no avenue for an operational response other than the anonymous internet...

Liability...your respective operations SOP, or an anonymous internet forum?

23rd Mar 2011, 02:32
Remember just this one thing:

If you get banjoed by lightning, word your ASR defensively.

I wish I had.:sad:

Turning the gain down is useful as wx radar nowadays paints too much stuff red.

Think about turning away if its on your FAT. That 10 mins that you lose manoevering will be easy compared to one hour of form filling!

Capn Bloggs
23rd Mar 2011, 04:34
You would ask the question on a forum ( and F with the people that respond) rather than your chain of command?
Bit harsh there. Apart from JC's indiscretion with BOAC, I see no problem with people asking advice here. Who knows, maybe he has already asked his "chain of command" and got nowhere? Quite possible these days.

Why not tap into the global knowledge available on Tech Log? If nothing else, some good links have popped up.

23rd Mar 2011, 06:03
global knowledge...good idea

and no one has said always make sure to be painting something, even if distant ground clutter.

While out flying near Baltimore, Maryland, USA, I heard some American Airlines pilot complaining that her wx radar wasn't working and asked ATC to point her at some weather to make sure it was working right.


Loose rivets
23rd Mar 2011, 06:37
A bit of light relief here.

British Eagle (second biggest local carrier after BEA/BA) had a fleet of Viscounts. When a 12" dish was developed, they opted for those. The trouble was they had been the only ones to own the old jig for building a pressurized bulkhead for a raydome. They'd sold it for something like 14k quid. When they got Marshalls ???? to do the work, they cost about that each to do the job. They kind of worked.

When we got the first (all green) digitals, we thought we were in the modern world. Little blocks of square pixels used to flash if the return was too great.

Into the flightdeck comes the head opps bloke. Look at that! I'd say. That little flashing rectangle is Buckingham palace. This one, Westminster. When they flash, it means the Queen's in residence.

23rd Mar 2011, 09:43
Hopefully maintaining LR's efforts.......

Time to tell again the story of the grumpy Captain who's F/O (un-noticed) wound the scanner angle right down and immediate avoiding action was taken on the island of Jersey:)

Piltdown Man
23rd Mar 2011, 10:19
Fundamentally, the reason the Wx radar is fitted is so we can avoid turbulence associated with Cbs. So, the first thing you should determine (from the met briefing pack) is the likelihood of their presence. Also, you have don't have to have rain to get a ride that will make your eyeballs hit their limit switches.

So, moving on it's not the colour per se that determines the movement of the air around the water that is displayed on the display. I'll give you that white/magenta or what ever colour is designated to the highest return, is probably due to rainfall from Cb, which are probably best avoided, but not always. What you need to avoid are the areas containing sudden and abrupt transitions in the patterns displayed. Avoiding an area purely due to colour alone may only add to track miles and give no smoother ride. Hooks, swirls, solid lines and areas with high contrast are also best given a wide berth. And here's the weird one, not all Cb's give a rough ride. But I'll be buggered if I can tell which ones are the friendly ones in advance.


Escape Path
24th Mar 2011, 05:09
From the Airbus document on weather radar use:

Climb: Select negative tilt, maintain ground returns on top of ND as the aircraft climbs

I'm not following. Shouldn't that need excessive negative tilt and would set the radar to scan what the aircraft is leaving below instead of scanning what one is going to fly through up above? Or is it because the radar will give a better indication of what is above by showing what is below (the lower the moister)?

Escape Path

24th Mar 2011, 13:12
by tilting down, you insure that the radar will paint a bit of the ground at the farthest range. in this way you know you are getting something. what if you had tilted so high that you got nothing...and smacked into a cell/

next time you fly on a nice day, ask the captain if you may experiment with the wx radar...tilt it, paint the ground, try different gain settings on distant , visually observed cells,

and please, look at the boundries between colors...it is the boundries which are often the most turbulent.

Piltdown Man
25th Mar 2011, 11:22
Escape Path: By setting your radar so that ground returns are shown on the top of the ND (ie. at extreme range) means that anything showing before that return will be a valid "sky" return. It's one method of optimising the tilt, valid for each range setting.


Capn Bloggs
25th Mar 2011, 15:02
I'll probably get shot down, but I reckon most of the Archie stuff is a WOFTAM. I do exactly as Scarebus does; put the ND on a reasonable scale eg cruise 160nm and put the inner edge of the groundline on the 80nm ring, full gain. Any return that comes inside 80nm is not ground, could be nasty and is dealt with. On climb and descent, at lower ranges, ground return on on the top edge of ND, for the reason Piltdown Man said. No need for mind-numbing tilt calculations.

25th Mar 2011, 15:24
all of this is fine, painting the ground at the edge is the right thing to do with the tilt.

Once you see a return/cell you can tilt up to see how high the cell might be.

now, using the gain. instead of the real reason to use the gain, think of it as an old time ''fine tuner'' on an ancient analog tv set. twist the gain slowly back and forth till the ''best'' image results. Especially with the most contrast (different color levels) between portions of the cell.

I am still convinced that the difference in colors at the boundries is the roughest spot. Why? The difference between the two boundries can almost be thought of as change in velocity of hydrometeors (raindrops). Its the difference that makes the bumps...some of the time.

oh well, back to sleep

me, I'm in the DCA tower on night duty...HA!

Loose rivets
25th Mar 2011, 18:27
Then there are the times that you may as well turn it off:

Briefly...North of Mont Blanc, in the stars way above some stratus. 5k' at least. Quite a light show showing trough the clouds. One core painting ahead.

Altered course to pass more than 10NM from the core. Suddenly, we fell down a series of concrete steps - each one having a thousand foot tread. My jacket floated on its hanger each drop.

There was no significant upper wind or orographic effect, just the storm a mile below.

25th Mar 2011, 20:11
Back to the OP's question - can it be said that stratiform rain clouds - oops, I mean nimbostratus - are not as likely to have the strong gradients and irregular contours?

[funny/] I had a Captain last summer ask me to request a heading to go around one of the two cells that was in front of us. At our 11 o'clock and 1 o'clock. That were moving with us. In a clear sky.

"Uh, Captain, I think those are cat eyes from the radome. . . ":ugh: