Bogus NEXRAD?

Jay Honeck

Jay Honeck

Touchdown! Greaser!
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Jay Honeck
Is it just me, or have NEXRAD displays become even more wildly inaccurate?

Example: On several occasions, most of South Texas has been covered with green and yellow splotches. No rain was observed.

Example: Flying back from Brenham, TX, both Garmin Pilot (via the Garmin GDL-39 ADS-B receiver) and our 496 (via XM) showed rain ahead. All we saw were puffy cumulus clouds.

Example: On our flight home from OSH, popcorn rain was displayed virtually everywhere along our 1300 mile route of flight. We saw one light rain shower.

In addition to being an annoying (and potentially dangerous) glitch for flying, this is hurting my business. No one comes to a beach community when the TV weatherman is showing a radar screen full of green blotches (as it does today) -- but I'm here to tell you that the weather is mostly sunny and hot.

Anyone know what's going on? It's like they've got the gain set too high, and they're interpreting thick clouds as rain.

Sent from my Nexus 7
 
Jay Honeck said:
Is it just me, or have NEXRAD displays become even more wildly inaccurate?

Example: On several occasions, most of South Texas has been covered with green and yellow splotches. No rain was observed.

Example: Flying back from Brenham, TX, both Garmin Pilot (via the Garmin GDL-39 ADS-B receiver) and our 496 (via XM) showed rain ahead. All we saw were puffy cumulus clouds.

Example: On our flight home from OSH, popcorn rain was displayed virtually everywhere along our 1300 mile route of flight. We saw one light rain shower.

In addition to being an annoying (and potentially dangerous) glitch for flying, this is hurting my business. No one comes to a beach community when the TV weatherman is showing a radar screen full of green blotches (as it does today) -- but I'm here to tell you that the weather is mostly sunny and hot.

Anyone know what's going on? It's like they've got the gain set too high, and they're interpreting thick clouds as rain.

Sent from my Nexus 7
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In SW Florida it seems to be pretty accurate, though XM Nexrad availability is intermittent at times. Calls to them just result in me spending an hour in my plane in front of my hangar waiting for the reset. So now I just hope it works when I fly.

When I can get ADS-B on my G1000 I am.

Doug
 
The sensitivity of the radar can, at times, cause it to show precip when it's just very humid. I have on many occasions had radar images showing rain when there was none. Also, and this especially applies in the summer, hot WX, virga will show up as precip (and it is), but it will have evaporated before it gets down to our lowly altitudes.

In our latitudes, green is rarely an issue, unless it is icing conditions.
 
SCCutler said:
The sensitivity of the radar can, at times, cause it to show precip when it's just very humid. I have on many occasions had radar images showing rain when there was none. Also, and this especially applies in the summer, hot WX, virga will show up as precip (and it is), but it will have evaporated before it gets down to our lowly altitudes.

In our latitudes, green is rarely an issue, unless it is icing conditions.
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Very true. Virga will show as rain but when you are on the ground you do not see rain. I usually ignore green because of this phenomena. However yellow will definitely have a substantial amount of rain and red would be pouring. I found that if you need to cross a red zone in a non turbo piston and it is too wide to deviate your best option is to go below the cell to avoid heavy turbulence, but keep an eye for a possible embedded tornado.

José
 
Another example. All day, NEXRAD has been showing moisture streaming in off the Gulf. As a result, the island is dead, dead, DEAD. No one in San Antonio is going to say "Hey, let's go to the beach!" when they see this sort of weather on the tube.

But...it's not raining. It hasn't rained yet. It probably won't rain. It's just a high overcast -- perfect weather, really.

Argh.
 
Piloto said:
Very true. Virga will show as rain but when you are on the ground you do not see rain. I usually ignore green because of this phenomena. However yellow will definitely have a substantial amount of rain and red would be pouring. I found that if you need to cross a red zone in a non turbo piston and it is too wide to deviate your best option is to go below the cell to avoid heavy turbulence, but keep an eye for a possible embedded tornado.

José
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So far in 85 hrs my nexrad has been right on the money, of course with a 10 min lag.

Jose, If it is showing red I am going to find a place to land as downdrafts/visibility can kill me.
 
RV10flyer said:
So far in 85 hrs my nexrad has been right on the money, of course with a 10 min lag.

Jose, If it is showing red I am going to find a place to land as downdrafts/visibility can kill me.
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True. In the plane, if there are reds on XM and/or ADS-B, it has ALWAYS been correct. And I get the heck out of Dodge.

I'm talking about greens, primarily. NEXRAD just seem to have it set so that it reads high humidity as "rain", which is misleading.
 
RV10flyer said:
So far in 85 hrs my nexrad has been right on the money, of course with a 10 min lag.

Jose, If it is showing red I am going to find a place to land as downdrafts/visibility can kill me.
Click to expand...

You may encounter instances where landing is not an option like on oceanic crossings. It happened to me on a radar equipped B58 enroute from LPAZ to CYYT. I based my decision to go lower on my experience on flight testing the new predictive windshear radar. As you go lower in altitude and since wind can not flow through earth the down draft vertical component changes to a horizontal component which cause the windshear effect. Windshear can have catastrophic effect on heavy airplanes but not on light planes like a Baron. You will still have turbulence effect but much less than inside the cell. Nevertheless the best option is to circumnavigate the weather and I found XM to be the best tool for the job.

José
 
What is the weather channel forecast?
Jay Honeck said:
Another example. All day, NEXRAD has been showing moisture streaming in off the Gulf. As a result, the island is dead, dead, DEAD. No one in San Antonio is going to say "Hey, let's go to the beach!" when they see this sort of weather on the tube.

But...it's not raining. It hasn't rained yet. It probably won't rain. It's just a high overcast -- perfect weather, really.

Argh.
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I'd be willing to bet that WC wields far more influence on travel plans than XM.

Jay Honeck said:
Same thing. They show the same Nexrad radar that we all see nowadays, showing rain everywhere.

It STILL hasn't rained here.
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Dunno, but figured out long ago that WC's forecasts are incredibly pessimistic, with multi-state green blobs on cavu days.

It occurred to me that the their dour outlook might possibly be related to the fact that when the weather is great there's no reason to continue to watch their channel. But I'm somewhat skeptical by nature, so maybe they are just more conservative than others. ;)
Jay Honeck said:
No doubt about that. But I think both XM and WC are using the same Nexrad data nowadays, aren't they?
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wabower said:
Dunno, but figured out long ago that WC's forecasts are incredibly pessimistic, with multi-state green blobs on cavu days.

It occurred to me that the their dour outlook might possibly be related to the fact that when the weather is great there's no reason to continue to watch their channel. But I'm somewhat skeptical by nature, so maybe they are just more conservative than others. ;)
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Nope, you're right. In Iowa, especially for the last ten years, every regular snow storm was pronounced to be a "LIFE-CHANGING EVENT" instead of a regular snow storm. It was weird, but it sold a LOT of advertising.

And younger, more susceptible people would flock to the grocery stores and buy them out of milk, as if we would all be stranded in-doors and without power for WEEKS. :rolleyes:

Down here in Texas, where the weather is incredibly benign and virtually unchanging (how do you say "Sunny and hot" a hundred different ways?), the forecasters just about cream their jeans when any sort of "real weather" comes our way.

This is why a hurricane hitting MEXICO is big news that causes people to buy water and stock up on plywood. When I mention that the storm is clearly visible on radar, and it's 600 miles away and likely to miss us by even more, no one cares because THIS IS A LIFE-CHANGING EVENT! And more people watch TV, which sells more advertising.

People are just plain stupid when it comes to weather and geography.
 
Jay Honeck said:
Another example. All day, NEXRAD has been showing moisture streaming in off the Gulf. As a result, the island is dead, dead, DEAD. No one in San Antonio is going to say "Hey, let's go to the beach!" when they see this sort of weather on the tube.

But...it's not raining. It hasn't rained yet. It probably won't rain. It's just a high overcast -- perfect weather, really.

Argh.
Click to expand...

Other than the delay in the system I have found it to be pretty accurate. Unfortunately I think there is going to be more people get into trouble with it thinking they can penetrate lines with accuracy.


Sent from my iPad using Tapatalk HD
 
Piloto said:
You may encounter instances where landing is not an option like on oceanic crossings. It happened to me on a radar equipped B58 enroute from LPAZ to CYYT. I based my decision to go lower on my experience on flight testing the new predictive windshear radar. As you go lower in altitude and since wind can not flow through earth the down draft vertical component changes to a horizontal component which cause the windshear effect. Windshear can have catastrophic effect on heavy airplanes but not on light planes like a Baron. You will still have turbulence effect but much less than inside the cell. Nevertheless the best option is to circumnavigate the weather and I found XM to be the best tool for the job.

José
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You can do what ever u want but I don't think that is great advice to be giving to others. Winds hear affects all airplanes and not just big airplanes. If anything they have an advantage because of windshear alerting systems and excess power to use if necessary.


Sent from my iPad using Tapatalk HD
 
flyingmoose said:
You can do what ever u want but I don't think that is great advice to be giving to others. Winds hear affects all airplanes and not just big airplanes. If anything they have an advantage because of windshear alerting systems and excess power to use if necessary.


Sent from my iPad using Tapatalk HD
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Due to more sluggish jet engine response and higher inertia, airliners are much worse off in wind shear. I agree with Jose about descending only if there is no other options and also about lighter aircraft being better off.
 
RV10flyer said:
Due to more sluggish jet engine response and higher inertia, airliners are much worse off in wind shear. I agree with Jose about descending only if there is no other options and also about lighter aircraft being better off.
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Well you can agree with whoever you want, but the fact of the matter is that most of the airplanes flown on this forum do not have the performance capabilities to overcome certain weather conditions. A 30kt loss of airspeed will affect all airplanes with a 30kt loss of airspeed no matter how big it is. In an airplane with a small margin of airspeed operation this will become an issue. In the same area you are going to get the wind sheer, a 1000fpm downdraft will not be overcome by an aircraft that can only climb 700fpm on a good day. Windshear avoidance systems on larger aircraft as i'm sure you know will trade airspeed for altitude and altitude for airspeed depending on the regime of flight and continued analysis of the changing conditions as long as you fly the eyebrows. To address the sluggishness of turbine engines. Most of the time the engines are not kept at idle to makes sure int approach phase of flight that if immediate power is needed that the delay is even shorter than normal. But most of the newer engines have minimal lag to speak of, so that is not going to be the downfall of the larger aircraft. But I'm sure you knew that also so with all that said, all I was trying to say to Jose was that its not very good advise to go under these types of weather systems and get that close to the ground. Now every body has to be there own PIC so you can make you own choices. Just wanted to clarify some things

Cheers
 
This one is pretty accurate. Run away! :D

uploadfromtaptalk1348961068293.jpg

We are under the blob NE of Corpus Christi. You can't even see the island in this pic, for all the red.

Sent from my Nexus 7
 
Not so. Windshear models are the same for all simulators. Small planes are capable of avoiding many crashes that bigger planes cannot.

planes
flyingmoose said:
You can do what ever u want but I don't think that is great advice to be giving to others. Winds hear affects all airplanes and not just big airplanes. If anything they have an advantage because of windshear alerting systems and excess power to use if necessary.


Sent from my iPad using Tapatalk HD
Click to expand...
 
Matt (flyingmoose)

Wayne comments on windshear are very correct. The reason why windshear has less effect on smaller aircraft is due the lighter mass thus less inertia and piston engines respond much quicker than large jet engines. As the wind flows changes from a headwind to a tailwind the lighter airplane can accelerate quicker than a heavy one. This causes a dramatic air speed change of 50kts to 80kts on the airliner causing it to stall and loose altitude.

To help overcome this situation reactive windshear equipment was mandated. But the problem with reactive windshear is that it only alerts you when you are in it. Pilot has to be very quick on responding to it and the jet engine slow spool up does not help.

The development of Doppler radar lead to the development of predictive windshear radar that can detect a windshear event up to 10nm away. I was involved with AlliedSignal (now Honeywell) on the development and flight testing (Convair 580 N580AS) of the RDR-4 Radar system. Unlike a jet plane the Convair 580 turbo prop uses constant speed engines that allows for a quick response during windshear testing.

Windshear happens at low altitudes and it is a hazard when on the approach or departure path of an airport where airliners are flying at low airspeeds.

In a light aircraft the effect of windshear is a short duration of loss in airspeed (momentary stall warning) followed by an increase in ground speed (tail wind). This will cause a longer than normal ground run and maybe some bouncing.

Windshear events are of short duration (10min) and many airports have wind sensors on the perimeter of the airport to alert pilots.

You can read more on the subject at:
http://en.wikipedia.org/wiki/Airborne_wind_shear_detection_and_alert_system

José
 
scottd said:
What's the source of your data? Date and time? Some websites you will see a highly filtered display. They will tend to filter out non-precipitation returns. But, that also filters out other important details such as outflow boundaries and gust fronts. Personally, I'd rather have the unfiltered data.
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As would I. I cannot believe the number of people who just look at a radar picture, in whatever display it happens to be, whenever they see it. But, nobody will take the time to look at it, what it means, nor have they ever looked into what different VCP's do.
 
Piloto said:
Matt (flyingmoose)

Wayne comments on windshear are very correct.
Click to expand...

He didn't say anything other than small airplanes are not affected as much. If there is data for this I would like to see it. Would be interesting.

Piloto said:
To help overcome this situation reactive windshear equipment was mandated. But the problem with reactive windshear is that it only alerts you when you are in it. Pilot has to be very quick on responding to it and the jet engine slow spool up does not help.
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Not true. The new systems will give resolution advisories like TCAS to help resolve the situation. Yes I have used it.

Piloto said:
Unlike a jet plane the Convair 580 turbo prop uses constant speed engines that allows for a quick response during windshear testing.
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Ok so I have about 600Hrs in the Convair 580 and it does not have constant speed engines. Constant speed props yes.

Piloto said:
Windshear happens at low altitudes and it is a hazard when on the approach or departure path of an airport where airliners are flying at low airspeeds.
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No Kiddin?

Piloto said:
You can read more on the subject at:
http://en.wikipedia.org/wiki/Airborne_wind_shear_detection_and_alert_system

José
Click to expand...

I don't need to read more on the alert system I have used it.

I don't want to derail this thread further than it is. Like I said before, It does not matter to me what you want to do. So unless you have some kind of data showing this I don't want to get off subject. And if you do then we can start a new thread about it. I hope you do because i would find it interesting and maybe learn something.
 
Light aircraft have propellers. Propellers provide at least a small portion of the relative wind over the center of the wing. Full-throttle, a single engine prop aircraft gets at least some fraction of its lift by accelerated air over the wing center by the prop. You get hit by a microburst you have instantaneous power response and some of that power is helping glue air to the wing.

In a typical transport category jet, the wing gets no help from pylon mounted engines underneath the wing, and the spool up time required to go to full thrust means you're not able to "hang it on the prop" until the acceleration overcomes the lost lift.

Ask me how I know this. I had to have the seat cushion surgically removed. If I'd have been in a jet, I'd be dead. No kidding.
 
Delta 91's WX model is standard in most Part 142 sims and I'm told is also part of most 121's. King Airs will fly out of much deeper penetration than will jets. Other models produce similar results. I assume some weather events will kill anything that's flying as well as most of what's on the ground beneath.

scottd said:
Wind shear comes in all shapes and sizes. You can bet that small aircraft would not survive at a low altitude in the presence of a microburst where downward winds can approach 100 mph in a matter of seconds. This kind of fury happens in what can appear to be very benign-looking conditions as I describe here.
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flyingmoose;994671]He didn't say anything other than small airplanes are not affected as much. If there is data for this I would like to see it. Would be interesting.

Check on this http://www.asc.gov.tw/author_files/WINSHEAR.pdf is pretty interesting. No mention of light airplanes of 12,500 pounds or less.


Not true. The new systems will give resolution advisories like TCAS to help resolve the situation. Yes I have used it.

The most popular reactive windshear system is the Honeywell MVII http://www51.honeywell.com/aero/common/documents/Mk_V_VII_EGPWS.pdf which also combines the terrain awareness and ILS deviation alerts. We had one in N580AS and never got an ahead warning in 28 windshear encounters in Denver and Orlando. The MVII is a pure reactive system.


Ok so I have about 600Hrs in the Convair 580 and it does not have constant speed engines. Constant speed props yes.

The Allison 501 engines are single axial shaft geared to the prop by a 10:1 gear. If the prop speed is constant so is the engine. Power is adjusted by controlling the engine torque (blade angle). This is the same concept as in piston engines with constant speed props, where power is adjusted by controlling torque (indirectly indicated by manifold pressure). Because the engine speed is constant there is no spool up delay.


I don't need to read more on the alert system I have used it.

Unfortunately I am not as smart as you or as young so I have to keep reading to keep current.

José
 
Jay, how is the NEXRAD looking today now that PWAT levels are down?
 
RV10flyer said:
Jay, how is the NEXRAD looking today now that PWAT levels are down?
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Today was a complete JOKE. Both the 496 and Nexus 7 showed widespread precip, while we saw only sunshine. We got a FS briefing, and they cautioned Mary on the rain in the area. When we informed them that NEXRAD was reading something that simply was not there, they had no comment.

I took pictures of both displays, and the view out the window of the plane. I will try to post them later.

Sent from my Nexus 7
 
Jay Honeck said:
Today was a complete JOKE. Both the 496 and Nexus 7 showed widespread precip, while we saw only sunshine. We got a FS briefing, and they cautioned Mary on the rain in the area. When we informed them that NEXRAD was reading something that simply was not there, they had no comment.

I took pictures of both displays, and the view out the window of the plane. I will try to post them later.

Sent from my Nexus 7
Click to expand...

I've noticed the same thing in my area, even very heavy returns with little to no precip either on the ground or in the air (and no visible virga, either).


JKG
 
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Okay, below are the pictures. If we had taken NEXRAD and Flight Service seriously, we would not have flown to our biennial flight reviews today. I have NO idea why the displays/returns were so wrong, but it was evident on both XM and ADS-B.

Here is the 496 XM radar depiction:

74859_436624273040139_1907602356_n.jpg


Here is the ADS-B radar depiction on the Nexus 7:

250516_436624079706825_1352547405_n.jpg


Here was the view out the window. It was sunny and gorgeous all day, and the view was the same out the side windows:

298561_436624723040094_362639783_n.jpg
 
I looked at several other WSR sites(base reflectivity) this morning and yours definitely needs some work. It is in clear air mode(slow). How does it do when you actually have storms out there? Do the returns always show up in the same areas? I would contact the NWS with this info. I can see where it could definitely keep people away. My HVAC business has been slow for 3 years, it is not wx related though. Good luck getting it fixed.
 
Jay Honeck said:
Is it just me, or have NEXRAD displays become even more wildly inaccurate?

Example: On several occasions, most of South Texas has been covered with green and yellow splotches. No rain was observed.

In addition to being an annoying (and potentially dangerous) glitch for flying, this is hurting my business. No one comes to a beach community when the TV weatherman is showing a radar screen full of green blotches (as it does today) -- but I'm here to tell you that the weather is mostly sunny and hot.

Anyone know what's going on? It's like they've got the gain set too high, and they're interpreting thick clouds as rain.
Sent from my Nexus 7
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Check this out. I am no weather or radar expert, but it is obvious your nearby radar site is different from the rest of the country and needs to be addressed.

http://radar.weather.gov/Conus/index_loop.php

I don't plan my trips with radar only, but I know many who do. How many pilots know where every WSR site is, and that all of this green is just a normal feature around this particular site? It appears mostly blue is the norm.
 
On occasions blowing sand or dust can create the same green returns you see on the screen without having any precipitation or virga effect.

José
 
So the question becomes, if it's that common, why isn't it filtered out?

(I've watched it for years here in Denver, also... we not only get ground clutter of the sort shown in the above examples, but you can clearly see the outlines of the Front Range when the low angle radar imagery is utilized to feed the national mash-up maps. It's not like the mountains move around a lot...)
 
Fair enough.

I can't say as I know many customers of the "products" who would know what they were seeing if they saw a gust front on a national radar composite, but you're one of the folks trying to change that, and teach us dumb pilots something, so I certainly respect your opinion that the data should be there and appreciate your efforts. :) :) :)

Most of us mentally filter it out anyway.

Jay's issue stems from the general public seeing scary green blobs and not wanting to come to his hotel, and the briefer for his recent flight being clueless.

Both of which aren't really NWS' issues to address. Heh. ;)
 
Scott,

We appreciate the education on here! I am just getting into soundings after four years of flying and they sure provide alot of info. Look forward to more threads like this.
 
Note that ground clutter (which we see here all the time, and are quite familiar with) generally produces a speckled blue radar return which is largely unmoving and persistent. On a time loop it looks almost "sparkly", and all local pilots know to discount it.

This was different. The returns we saw yesterday were two shades of green, and moving. Completely different from the usual ground clutter. The photos aren't the best, but if you look closely this is NOT ground clutter.

FS interpreted what they were seeing as rain, but they were just as confused as we were, since all of the reporting stations were calling "skies clear" beneath the green blob.

Ground clutter this was not.

Sent from my Nexus 7
 
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