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As a pilot, at what point of their formation, cumulus clouds start worrying you when you're out flying? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.
Answer by Joe Shelton, Author, Pilot, Aircraft Owner, on Quora:
The question is: As a pilot, at what point in their formation do cumulus clouds start worrying you when you're flying?
This is a difficult question to answer because cumulus (Cu) clouds span a very wide range of instability. Some Cu grow quickly, some not so quickly. Some grow very tall (think thunderstorm), some not so tall. Some grow alone while some are part of a wide area unstable airmass. They’re all different. Worse, the turbulence in a strong and fast growing cumulus cloud like a thunderstorm can potentially destroy an aircraft.
From a pilot’s point of view, the bigger and taller it is from base to top, the more dangerous it is. The big ones, sometimes passing 40,000 feet, are capable of making any flight through it uncomfortable and potentially deadly. The good news is that most cumulus aren’t that big, nor that dangerous.
Here’s the thinking I would use when planning how to deal with cumulus clouds.
If any part of a cumulus cloud is at your altitude or higher, no surprise, stay away, especially if you aren’t IFR rated and on an IFR flight plan. If there are other Cu in the area, plan to avoid them and always keep your eye open for an escape route. That usually means heading either where they aren’t or descending below the bases. Sometimes however, the best solution is a 180° turn back toward where you came from.
If there are lots of Cu in the area, be forewarned, mother nature has instability on her mind. Again, as you continue your flight keep looking for a new escape like an alternate routing or alternate airport. Decide on a trigger, like the percentage of the sky that is covered by clouds, and that criteria encourages that you will use the escape if it is needed. It doesn’t mean you’ll need it, but if you don’t have a plan things could get interesting, and not in a good way.
If there are lots of Cu in the area and many have tops that are higher than, say, 15,000 feet, think highly unstable, and maybe it’s time to get out of Dodge.
As a VFR pilot, never fly above a cumulus cloud deck or even try to climb above them unless you have an airplane that can climb strongly into the flight levels. Cumulus can often out climb general aviation aircraft and the tops can be higher than most general aviation aircraft can reach.
I’ve been at the certified ceiling of my Malibu (25,000 feet) and found I was “on top” of climbing undercast and couldn’t legally climb any higher. But I was in a valley of clouds where the tops in all directions were higher than my airplane. There’s often ice in the tops of Cu, so descending through 20,000 plus feet of ice and turbulence wasn’t an ideal plan. Instead, I climbed a couple thousand feet, eventually found an area where I could descend and, like I recommended earlier, got the heck out of Dodge.
It’s often turbulent under Cu and especially under mature thunderstorms. So, if possible don’t fly underneath them and always avoid flying under the anvil head even if you’re in the clear because of the potential for extreme turbulence and even hail.
Also, if you have the choice, fly upwind of cumulus because the worst turbulence is usually on the downwind side.
I’ve made hundreds of comfortable flights in and around cumulus so don’t think that every cumulus cloud can hurt you. Have a healthy respect, avoid the big and fast growing ones, have an alternate plan, and enjoy your flight.
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