First we received excellent Nexrad radar mosaic images from XM and Sirius satellites and the way many of us fly changed so much for the better. Now we can receive subscription free Nexrad from a variety of receivers listening in on the ADS-B ground station network. The resolution of the Nexrad picture on ADS-B isn’t quite as good as the pay-for-service satellite displays, but it’s still plenty good.
But, no matter how good those Nexrad mosaic radar images are, there are days when nothing does the job like a radar on your airplane. Last Thursday evening was one of those days for me.
The sun was setting when I took off from Oshkosh headed east for home at the Muskegon County Airport on Lake Michigan’s shore. The rain was moderate over Oshkosh and clusters of cells extended across Lake Michigan all the way home.
The precip was associated with an almost stationary cold front so severe weather wasn’t expected, but there was some lightning about as proof of embedded thunderstorms, and level three and even four radar returns are hardly ever anything but a very rough ride even if the rain isn’t really in a thunderstorm. There were ways around the cells, but the trick was to find them.
I’m lucky enough to have both satellite weather in the panel, and a Garmin GWX 68 digital weather radar in the nose of my Baron. I have to say that the radar spends most of my flight hours idling away in standby mode. Usually when storms are about the satellite Nexrad shows how to make the big course changes that avoids the precip.
But on this day some of the cells were growing with unusual speed. As I flew through light to moderate rain in an area where satellite Nexrad showed no precip, I knew it was time to take a close look at the GWX 68. Sure enough the onboard radar showed returns changing from level one green, to areas of level two yellow, then to level three red in a minute or less. The cells return intensity was changing with every sweep of the radar.
The good news is that the cells were isolated in either an area clear of precip, or embedded in larger areas of light precip, so I could go around them with relatively small heading changes. At one point I popped into the clear and there was just enough light left to see the boiling mass of a building CB exactly where the GWX 68 showed a level two and three cell to be. No pilot would have flown into that cloud if he could see it, but with only satellite Nexrad to go by, I could have nailed the storm in the belly button.
After about 10 years of cockpit satellite weather the NTSB has figured out what most of us have known for years—the Nexrad mosaics sent to the cockpit are many minutes old by the time we see them. The Board has gone into full arm-waving warning mode about the “latency” of these satellite radar displays because during a couple investigations it found that pilots equipped with satellite weather may have nailed a thunderstorm that grew between new radar pictures. In other words, the NTSB has documented what we should all have known—satellite Nexrad is reliable only for wide deviations around storms, not for up close tactical maneuvering.
Onboard weather radar is expensive, and most singles can’t carry a radar, but it is the answer for close in storm avoidance. That’s why Garmin announced the GWX 70, a new solid state weather radar that presents an image more useful, and easier to interpret than the GWX 68.
The GWX 70 eliminates the vacuum tube—called a magnetron in radars—in favor of solid state devices to power the transmitter. That means the GWX 70 broadcasts a coherent signal. When energy is reflected back to the GWX 70 antenna the brains of the system analyze how the frequency of the transmitted signal changed. By looking at frequency changes the GWX 70 can tell the difference between ground returns and precip, and automatically suppress the ground clutter so you see the precip. The system can also measure movement of droplets in the storm and apply Doppler techniques to determine the velocity of the moving drops and translate that as the probability of turbulence.
Other much more expensive radars designed for larger turbine airplanes have had these capabilities for several years, but the GWX 70 is the first “smart” radar aimed at the broader general aviation market. The GWX 70 is available with 10, 12 or 18 inch antennas so it fits in single engine airplanes up to larger business jets.
While there is still no such thing as “all weather” capability, a good radar such as the GWX 68, or even better the new GWX 70, brings you closer to that goal. Weather radar can’t make storms go away, but it can show you where they are in real time so you can go someplace else. So, which do you want, satellite weather or onboard radar? Like most things in life, you want it all.