By: Mac McClellan
I was flying my Baron home to Michigan from Savannah. A stationary front was hanging around across the Kentucky, Tennessee, Virginia border area. The forecast called for a chance of thunderstorms in the area of the front.
In other words, it was a pretty common late spring, early summer weather day across the southeast. Scattered sunshine, partly stormy, warm and humid and pilots can hope for the best and expect the worst.
Before satellite weather in the cockpit became available we had little choice but to plunge into that kind of weather, at least if we were flying instruments. If you didn’t, the wait to go may take days because that kind of front and system often moves or changes little.
If you were lucky enough to have weather radar onboard you could deviate around heavier rain, but still there was no way to miss the clouds that were wet and bumpy but did not contain water droplets large enough to show up on our radars.
With the introduction of satellite weather radar mosaic, that all changed. The weather service’s network of Doppler radars can detect the smallest rains drops. They can even “see” what I would call thick fog. And those radar returns get sent down to our cockpits as level one, or even level two, shades of green.
Now that I can see that there really is some kind of precip along my route—and often stretching for many miles either side of the route—what to do? I’ve often flown into areas of green satellite radar and never hit a bump. Often droplets don’t even hit the windshield. The precip the radars are seeing is either too light for me to detect, or more likely is contained in clouds above or below my altitude.
But sometimes a building convective cloud will contain only droplets small enough to show up as level one green. A building cloud only 10, 12 or 14 thousand feet high isn’t a thunderstorm—yet—but when you fly through it you sure wish you were anywhere else. The up and down drafts can be remarkable, and the turbulence where the drafts change places can smack your head on the ceiling.
So relying only on satellite weather showing green level one means you either cancel trips or make big deviations when there was no significant turbulence to worry about, or you fly into really bumpy and threatening turbulence. The only way to avoid either of those is to understand the overall weather patterns, and to study the shape and character of the radar returns.
If the forecasts along your route call for thunderstorms, you must beware of green radar returns. Unless you can visually avoid the building clouds, flying into a green return when conditions are right for convection will almost always result in a very rough ride.
When studying a radar return, it’s important to examine the size. A big, widespread level one green return is not threatening. Widespread light precip comes from stable, even subsiding air, and turbulence won’t be much of an issue. But if the green returns are small, or change from level one green to even level two green over a short distance, there could be big bumps. Convective clouds start with a small core of moisture and a small green return in an area of unstable air could be the birth of a thunderstorm.
For my trip home through the area of the stationary front, the level one green returns on the SiriusXM satellite weather mosaic were widespread with only small scattered areas of yellow. The rain was so light that the terrific Garmin weather radar in the nose could only show small areas of precip. And the drops hitting the windshield were tiny.
The ride was occasionally choppy but nothing even as bad as the low altitude turbulence caused by the thermals of a sunny clear day. The green was there, but an IFR trip through it was not only possible, it was prudent. Green returns must be taken seriously, but we can’t let them change all of our plans.
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