This is a reply  to my ADS-B/XM column

Interesting article.  I recently got to test both on a flight back from San Diego.  My ride to Montgomery could only get me there in the late afternoon.  Only isolated thunderstorms were predicted fo Phoenix, but Flight Service was wrong.  As I was the approaching Phoenix area, Sky Harbor started holding departures.  Deer Valley was clear but the weather was between me and Deer Valley.

 Both XM and ADS-B showed gaps in the weather.  The line of thunderstorms was moving NW at 15 knots.  Every time I got around a thunderstorm where a gap was supposed to be, it wasn't there.

Buckeye was now in the gust front, and I wasn't feeling very confident about either xm or ads-b readouts, so I asked ATC how Wickenburg looked.  My plan was to head NW and either get around the thunderstorms or land at Wickenburg and let them pass.  When I got within sight of the Wickenburg area it looked terrible.  ATC still said it looked good on their radar.  I guess theirs doesn't loop, or they would have seen that the storm was going to get there before I did.

 We ended up accepting defeat and went all the way back to Blythe to spend the night.  I was glad that I had plenty of fuel onboard.

 Anyway, I found out that my I-pad ads-b only updates weather every 10 minutes.  I don't know how old it is at that point.  XM weather updates more often, but again I don't know how old it is at that point either.  Neither one is very accurate if the weather is moving or developing very fast.  I believe some ATC facilities are able to get the NEXRAD feed, and if they are using that they are not getting current weather either.

 Sorry for the long message, I just started to say that I liked your article. 

Take Care,