When you call for a preflight weather briefing, information about the height of cloud bases and the extent of cloud cover helps you make your go/no-go decision.
What about cloud tops? Flying above cloud layers is not routine for student pilots—and the federal aviation regulations prohibit it "when the flight cannot be made with visual reference to the surface." Yet many pilots hoping for a complete weather picture ask how to find information about cloud tops.
"But that's precisely the problem. For all the meteorological advances in recent decades, apparently very little effort has been put into technologies that could help us in this regard. So for the near future, anyway, we're left to rely on just a few sources of information about tops," including area forecasts, radar summary charts, satellite imagery, atmospheric soundings, and pilot reports (pireps).
An area forecast (FA) is the most familiar of these resources. Cloud top information found in the fourth section of an FA is general. That's because the FA "gives a picture of clouds, general weather conditions, and visual meteorological conditions (VMC) expected over a large area encompassing several states," explains Chapter 10 of the Pilot's Handbook of Aeronautical Knowledge.
Pireps help, but Horne offered this reminder: "Pireps promise the most accuracy, but please check the dates and times of any pireps. It's not unusual for pireps to be a day old, yet still be posted. The problem with pireps is that most pilots never make them, so we are deprived of good cloud-top information by some of the best weather observers in the world."
Why is flying VFR above clouds discouraged for the inexperienced pilot? One risk is becoming trapped above a scattered or broken cloud cover that unexpectedly closes up to solid overcast. But even when breaks remain, pilots have encountered spatial disorientation and lost control during descent, as documented in this accident analysis. Steering well clear of all clouds remains the best bet.
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