Nexrad interpretation?

[Rich Drewes]

Hello,

I've been using Avare for a while and it is generally very good for my uses. Thanks!

One concern I noted recently though: the Avare Nexrad layer doesn't seem to look like the Nexrad data from DUATS, or at least I'm not sure how to interpret it the Avare Nexrad. For example, right now, on Avare the Nexrad looks like this:

This looks like lots of weather (blue, white and a bit of green) near the center of the image. However, right now the Nexrad from DUATS on the web looks like this:

It shows basically clear. Just a tiny bit of green at the moment, but I have seen cases where it is totally clear on DUATS but lots of heavy blue in Avare.

My pilot friend uses Foreflight, and his display looks like DUATS's display: basically clear. Is it the case that Foreflight and DUATS are only showing precipitation and filter out stuff that Avare shows in blue and white? I can reconcile these two views if the Avare Nexrad is showing blue as some very light mist condition, or something like that, that the DUATS Nexrad does not bother to display. Is this what is happening? If that is what Avare is doing, then it seems to be at odds with "normal" aviation Nexrad.

What is the actual source for the Nexrad data that Avare uses?

Thanks,

Rich

[Zubair Khan]

Hi 

Maybe Duats and FF look same because they have same source?

Avare displays from https://radar.weather.gov/Conus/

Thanks

Z

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[Peter A. Gustafson]

Avare uses the national mosaic enhanced radar image (https://aviationweather.gov/radar/mosaic).  Attached is the associated image for your question.  I'm not sure what DUATS and others use as their source.

[fly...@yahoo.com]

Hi Rich and everyone.
I am not sure what filter is FF and others is using but I can tell you of a recent experience that I had flying over LAX with a buddy of mine, this past Saturday actually. We looked at our devices and his FF showed clear over LAX SVFR corridor and Avare showed some layer going from the shore to CNO airport. We took off from KFUL flight following to KIZA and as we got over KLGB we could see a layer between 3-5000Ft, very close to what Avare depicted. We ended up going to another airport. The layer cleared about 4 hrs. later, but we were on the way back by then.
This is Not intended to justify, or say that there may not be some issue with the Avare depiction, that may at some point be improved if found to be overdone, just my experience.
The pic attached shows the Sat image around 1700Z, about the time you looked? TV

[Roger R]

I think the 'problem/difference' is the in the use/choice of which radar image to use. The one is Z's link above according to dBz values likely indicates dust, smoke, bugs, maybe even AP....you have to compare to svrl diff images....to see what is going on. 

For  instance right now if you go to https://aviationweather.gov/radar you see svrl diff radar images....the one used by Z above in my mind does not accurately indicate actual precip. You can see this by looking at other (kinds of) radar images on the the same site...also by looking at the dB values/colors...see here too.... https://www.wunderground.com/prepare/understanding-radar

also you can cross check the area forecast for California---clear with some smoke around in the area of indicated returns; and TAFS and Metars and verify there is no precip. I suggest using drop down tabs at top of the page in my first link above....see specifically under the forecasts button----TAFS, Area Forecasts, and Aviation forecasts; and under Observations see Metars, Cig/vis, and radar, even satelitte....all these show that there is nothing going on...it is essentially clr. Also you can see  http://www.aviationweather.gov/gfa, one of my fav wx briefing sites and check the buttons for pcpn/wx, cig/vis, clouds, TAFs (if the forecast button is selected)...you can zoom in to a narrower area and many more TAFs and Metars will pop up....from all this cross checking you have given yourself a much better handle on the wx AND shown that the radar image chosen/presented is not really showing precip  and that just looking at colors is not necessarily helpful....you have to cross check and you have to know what the colors mean and a little more about how wx radar works.  

I would choose to display a diff radar image rather than the one used according to Z's link. It is on the face of it misleading and can cause confusion. Still it is the pilots responsibility to understand and cross check this stuff. IMHO.

Roger

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[Zubair Khan]

OK thanks for the info and clarification. At this time we will keep it to current source. You may disregard white and blue areas as dust, smoke, fog etc. Start with green as precip, then yellow as medium precip, and red as dangerous convection. Combine that with Airmets and Sigmets overlay in Avare weather to get a better picture of precipitation and IFR. You may also want to check Briefing and various weather charts under Plan.
Regrads
Z


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-------- Original Message --------

[Roger R]

There seems to be a mixing of terms---Satellites generally show clouds; Radar/Nexrad generally shows precip and not clouds so you have to be using/comparing images of one kind, radar to radar and satellite to satellite not one to the other.  though each can be used to verify/cross check the other in some respects but they are not mixable/replacable one for the other. 

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[John W SBA]

> pilots responsibility to understand and cross check

That says it all, imo. Avare is a small, fast and relatively simple
app. For a fuller spectrum of wx info I always explore at least five
and often over a dozen online sources with a browser. I then use the
Avare wx as a reference for what was going on at takeoff, get flight
following whenever possible (assuming I'm VFR), and rarely will land to
update or find a spot where I can get data aloft (once by circling a
cell tower on a KS interstate at 2k' AGL). When in flight my primary wx
source is outside. Seems to me that for secondary sources anything
short of on-board radar and lightning detection is guesswork at best.

[bman]

Despite what naysayers try to do to decrease the value of ADSB provided weather, it is both timely and accurate. All radar, except on board which requires interpretation, comes from the same source - NEXRAD operated by the National Weather Service. Different vendors may display that data slightly depending on the algorithms their software. Avare uses ADDS from NWS so should be thought of as raw data.
NWS operators change NEXRAD station sensitivity (VCP) depending on current weather conditions. Generally they are either in clear air mode or looking for convection. A clear air VCP will display very light precip, clouds, dust, birds or smoke. Often you will see this displayed by what appear to be precipitation circles around the radar sites. There is normally little if any variation in what appears to be precip.
Foreflight and XM probably have software written at high cost to eliminate that display.
Once again, NWS is the source for all radar products, whether ADSB or circling a cell tower. Spend some time to learn what each product is doing to the raw data. ADSB is timely and accurate for strategic not tactical weather decisions.

[John W SBA]

> naysayers try to...decrease the value of ADSB provided weather

My own opinion is that it's very valuable, and my most frequent use of
ADS-B In when away from congested airspace. At the same time, the many
NTSB reports about over-reliance on radar being a factor in accidents
has me very cautious about in-flight decision making based on NEXRAD.

> NWS operators change NEXRAD station sensitivity...

Thanks for the helpful extra details on how it works in the field.

> Foreflight and XM probably have software written at high cost

Would you be willing to donate some coding to improve Avare's wx display
or add more options? If not, maybe help someone with the coding
expertise who'd be willing to do it?

> NWS...all radar products, whether ADSB or circling a cell tower

Thanks for clarifying. To clarify my circling comment, it was to enable
an update of wx downloaded in Avare before takeoff when I didn't yet
have ADS-B In. I also used that data connection to open several
bookmarked wx sites in Firefox on my phone, since as you point out they
offer different depictions and other details. I was glad to have more
information on nearly current data and trends before making the decision
to continue on rather than land.

> Spend some time to learn what each product is doing to the raw data.

Would you be willing to write up and post a more detailed summary, or at
least some references you've found helpful?

> ADSB is timely and accurate for strategic not tactical

I agree, FWIW. :)

Thanks for your posts on this important topic.

[bman]

The detail I offered comes from my experience as a CFII. Most of that info can be gleaned from Internet sources. The important thing is to know exactly how each software depicts the NEXRAD data. Avare appears to use raw ADDS data so a lot can be gained from the information pages at ADDS and NWS. It is also important to understand that each software depiction WILL be slightly different. That is not unlike the fact that different weather briefers will present similar data with a different emphasis.

I suspect you would find many accidents that occur because of reliance on tech happen because of trying to make tactical route decisions based on NEXRAD given by either ADS-B or XM (like you would with real time on board radar). If you approach the data offered strategically with the decisions made to avoid all precip when any convection is present or simply land, you will go a long way to never being an NTSB file number.

My flying goes back to the days we didn't even have weather radar covering the entire 48 and no satellite views. We have come a long way! Still, we have to be careful to fully understand what our tech is telling us.

Unfortunately I know nothing about coding - note the age indicated above. :-)

[John W SBA]

> never being an NTSB file number.

A goal we share. ;)

> My flying goes back to the days we didn't even have weather radar

That's a LOT of experience, and I appreciate you sharing it. :)

Happy Flying -j