Some big thunderstorms just passed through our area (GSP). I had live doppler at my desk and noted that the info was too slow in coming to be particularly useful. The cycle time for the NWS dopplers seems to be about 4-7 minutes. My understanding is that ALL datalink doppler services providing radars get their data feed from NWS. I was imagining flying in this area with a doppler datalink. I think the combination of ground speed of three miles per minute combined with data up to 7 minutes old would leave me very ill at ease. It would certainly be good enough to know to turn around and go the other way, but would not be adequate for information sufficient to pass 15 miles between the cells. As a supplement to onboard real time information it would help. Of course more information is usually better but I don’t think it’s worth its price for the role of weather avoidance. Perhaps worth it for its other functions though. Do any of you have personal experience with a data link system? Any advice about vendors? Thanks for your thoughts.Clark Jernigan

(1) As I understand it, not all datalink radar is routed through the NWS. Don’t know who it DOES come from, but I remember reading in a AOPA pilot article a while back that private vendors provide data feed services to companies like AirCell.

(2) If your “live” doppler radar image feed is coming in from a free internet site, of course its time-delayed. (The commercial providers can’t charge their customers for it very well if the customers can get it for free in real-time over the 'net!) If you look at the 5 min summary loop on most DTN or WxBrief terminals at FBOs, you’ll see that the delay time is on the order of 90 - 180 seconds. Most Nexrad images are on the order of 2-3 minutes delayed. Delay time varies based on where the actual radar feed originates and where its being fed to…

Fortunately the thunderstorms aren’t doing 3 miles a minute! Fastest moving one I ever saw was travelling at about 50 knots.

As I understand it, it takes the radome several minutes to compile the image we see, so I’m wondering if there’s the delay of sending it out on top of a delay to compile it. Even when I watch it in the weather station ( at the base of the radome in the NWS office) there is a delay.

Clark: I’m going to Oshkosh later this month. I will find out what I can from Avidyne. Avidyne has a subscription plan for the weather data. I believe the data they are providing is fairly current. Anybody know for sure?

Three miles a minute was the Cirrus traveling in the vicinity of the weather. With the big ones yesterday I would add a 1000 foot per minute downward toward the nearest airport!Clark