Look for rain or lightning?

Michael Oxner has a posting about the weather capabilities of Canadian ATC radar, and mentions that many pilots do not have weather radar on board.

That’s true — weather radar is pretty expensive — but a lot of us do have on-board lightning detection through a Strikefinder or a Stormscope. A mature thunderstorm cell will produce a lot of electrical activity and a lot of moisture, so either lightning detection or radar will help you avoid the real killer weather. The differences have more to do with comfort and convenience.

For example, weather radar can detect heavy rain showers without associated electrical activity. Heavy showers typically have moderate turbulence associated with them, and while that’s not very dangerous, it can make a serious difference for passenger comfort (and for yours, if you have to spend an hour cleaning up vomit after the flight). My Stormscope gives me no warning at all of embedded ACC or TCU without electrical activity. While I have no commercial experience, I imagine that if you are flying passengers in a charter or commuter air service, weather radar is a pretty obvious choice. Weather radar also allows you to check different angles — I’m not sure how easy that is to use, but at least in theory, it should be possibly to figure out how high up the weather goes. Lightning detection is strictly two-dimensional.

On the other hand, lightning detection works well even on the ground when the plane is surrounded by buildings, trees, or larger planes, so it’s possible to switch on the masters and take a peak at the weather around the airport before starting the engine. Weather radar can give a lot of false positives, since it cannot distinguish heavy rain from a thunderstorm; with a Stormscope (and a strong stomach), you can avoid some unnecessary diversions. Finally, a Stormscope can detect electrical activity in the early stages of a developing thunderstorm cell, when the cell might not be producing strong returns on a radar — again, this would be a case of avoiding moderate turbulence rather than preventing an in-flight breakup.

In an ideal world, you’d want both. For passenger comfort, I think I’d do better with radar, but the Stormscope is at least enough to let me fly in summer IMC, when I’d be uncomfortable relying solely on ATC (here’s why). Given that it would be fairly straight-forward to overlay Environment Canada’s weather radar on ATC displays, I find it interesting that Michael reports that Nav Canada has decided to show lightning strikes instead. I guess the rain-vs-lightning debate isn’t over yet.

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1 Response to Look for rain or lightning?

  1. John says:

    On-board radar is nice to have, but it has it’s limitations. One is attenuation, where an area of heavy precip masks an even stronger cell behind it. By far the biggest limitation of my on-board radar is that you only see 20 or so degrees either side of your current path – you don’t see what kind of weather is lurking on your wing tips until you are told to turn that way.

    The strikefinder is nice because it is omni-directional, which is a big advantage. I think the ideal setup would be radar, a strikefinder, and XM weather downloads with NEXRAD images. NEXRAD has it’s own set of issues (images can be several minutes old), but it gives you a more complete, 360 degree picture of what’s happening.

    I’ve found most U.S. ATC personnel are not really very good at telling you about areas of heavy precip, though they are good at passing on information about turbulence and icing reports made by other pilots.

    When I instruct in light aircraft that don’t even have a strikefinder, I’m very conservative in my decision making!

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