Why no green or yellow on NEXRAD?

[RobertE]

This morning I flew from southern Oregon to the Bay Area. For the first hour of flight I was in and out of showers strong enough to peal the paint from a dime sized area on the spinner. But neither onboard Sirius XM nor Foreflight on the ground showed even a hint of green. Anyone know what's up with that?

Maybe it's not relevant, but two days earlier while northbound much of the region painted green despite not a drop (it looked like high clouds might have had some moisture in them). My understanding is that NEXRAD shows a composite image but there is no way that 10,000 feet worth of vertical development dumping rain shouldn't show on a radar scope. No?

Can anyone explain?

Thanks.

[MooneyBob]

I posted the same question while ago as it happened to me too. I didn't get any answer that would satisfied me.

[Jeff_S]

Radar isn't infallible and sometimes goes out of service. If it didn't show on either service that was likely the case.

[M20F]

NEXRAD is strategic and will help you plan. Onboard radar is tactical and will help you pick through.

[Marauder]

Onboard radar is tactical and will help you pick through.

If you know how to use it correctly...

Sent from my iPad using Tapatalk

[carqwik]

Nexrad does not cover the entire USA...there are coverage gaps.  Or perhaps you were in an area where the radar is altitude limited? Note the big gap along the West Coast in Oregon for example...

 

[ArtVandelay]

ADSB has similar gaps in coverage:

https://www.faa.gov/nextgen/programs/adsb/ICM/

[RobertE]

Interesting if it was a radar outage but, according to the map, two sites - KMAX and KBHX - would likely have had to have been out of service.  And, boy, coastal Oregon sure doesn't seem to have much coverage below 10K.  Wow.

[kortopates]

I really doubt this was a Nexrad coverage issue unless we're talking about just southern Oregons coast. More likely I think the issue is Nexrad filtering. This really goes to the heart of why its important to not overly rely on what you see on Nexrad, you can exerperienvce the same missing returns with severe convective cells too. There is much written about differences in nexrad weather products available if you search around. But both XM and WSI due to their best to filter out non-precipitation returns that would otherwise really clutter our screens. Non-precipitation returns come from ground clutter, anomalous propagation, dust, birds and even birds. The nexrad service provider, WxWorx in the case of XM, has meteorologist that apply a gross filter to remove all returns over areas they believe has no precipitation. Of course the filters remove real precipitation too. So the problem then becomes how quickly they update the filters when precipitation begins. People have documented cases when they were seeing severe cells out the window (and even before takeoff on NWS nexrad) but their XM nexrad screen was showing nothing, then all of a sudden the filter is removed and now the Nexrad screens show severe cells. Usually  they are much more on top of things but given the human element of the filtering sometimes they are left when they shouldn't have. The opposite is true too in that all ground clutter is removed with the filter. So the bottom line is to not overly rely on nexrad; especially to keep you out of convective turbulence.

[RobertE]

Believe me, I had the stormscope on to keep me from convection (there was none) but for about 150 NM I was in and out of showers that came from clouds with 10K tops (maybe higher).  These had been around all morning, I think.  Yet no green or yellow either through Foreflight on the ground or in the cockpit via Sirius XM.  It does tend to erode my trust in Nexrad.  With the exception of once over central Nevada where it failed to show precipitation the only "errors" I've seen in Nexrad was it showing green when there was no precipitation to be found.  In those instances I've assumed that some wet clouds above were producing the returns.

[Mooney20]

Any of the NEXRAD products, regardless of the delivery mode, are history (about 15 minutes old) by the time it shows up on what ever display you are using. In active weather, that's an eternity. Don't rely on it in those situations, unless you want a nasty surprise. And there are coverage gaps as a poster earlier showed.

If you are lucky enough to fly from an airport with a Terminal Doppler Weather Radar (TDWR) nearby, it's a great resource for departure planning. Call it up on your smart phone while holding for takeoff. It's refreshed much, much more frequently and WAY more accurate than the NEXRAD composite.

[N201MKTurbo]

I've had a few opertunities to use the NWS radars. It kind of matters how the operator has it set up. If he has the antenna at a high angle he can see the tops of near by cells with good resolution. If he has it at a low angle it will get far off cells with a lot of nearby ground clutter. You can stop it and manually drive the antenna to get a good picture of a cell of interest. They can run it on automatic at a fixed elevation or let it scan up and down.

Unfortunately, we don't know how it is set up at any particular time. What we see is a computer generated composit of wherever the antenna has been pointed for the last 5 min or so.

I got to do this by walking up to the NWS buildings at different airports and asking if I could look at their radars. About half the time they will. Some of the guys ar so board they will show you everything.