Nexrad Interpretation


I wrote recently in Going Direct about interpreting Nexrad images and the NTSB's alert about image latency, that is the difference between published image age and its actual age.

I got a lot of responses from folks who were concerned about trusting Nexrad images at all. It’s an understandable concern, but if we place zero trust in satellite Nexrad, what’s the point of even having it in the cockpit. My point was that we need to use it but use it wisely, making use of whatever additional technology — Stormscope or onboard radar — we have to help confirm the location of cells.

On a recent flight from Orlando Executive to my fuel stop at Hammond, Louisiana, I was flying on an IFR flight plan at 8,000 feet in the Cirrus on V198. I knew in advance that there was a big developing system just north of Mobile that was moving slowly to the southeast. There was also a smaller but more active cell just off the coast that was moving south, so it was unlikely that it would turn around and cut off my beating the big cell along the coast. There was always the possibility of new cells growing as I made my way north up toward Tallahassee and then west "around the corner" along the Panhandle. I was able to keep an eye on the formation of new cells on the Nexrad on the Sirius/XM on the Perspective cockpit on my SR22.

I could also see that the big system was still north of my flight planned route and I got a good idea of just how fast it was moving south, though I wasn’t sure if it would make it to the coast before I made it there. To give myself several outs, I confirmed with ATC that I’d be able to deviate to the south of Mobile for the system. I also had a number of solidly VFR airports at my six o’clock, as well as a few good choices along the coast, not to mention good visibility on the ground just about everywhere but right under the active cells. I had no shortage of options if I were to get cut off or if the system were to start to build rapidly along my route, which is always a possibility with unstable conditions.

I made it by the storm with only miles to spare, though I always had, as I mentioned, a number of outs along the way, and I got into Hammond ahead of a good sized cell in time to get topped off and head out in clear air. I watched the lightning to the north as I banked west, called New Orleans departure for my clearance and started climbing up to 8,000 feet.

My trip continued like that all the way to Houston, dodging and weaving my way through the buildups the whole way, but always with a number of options should the scattered storms ahead suddenly become an impassable line.

It was a very busy flight, and Nexrad, despite it being much maligned of late, was a great tool not in telling me where to go but in helping me make deviation decisions in an informed way, the key being to use it strategically, getting a lay of the land from a long ways off before committing to a route and even then insisting on having a number of outs as I proceeded.


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