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Spring flying

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Active member
Nov 26, 2001
Spring flying question

As a newly minted instrument pilot I was wondering about what people in general aviation do when flying around towering (or non towering) cumulus clouds. I'm talking about a pretty good size buildup that isn't yet producing showers (or maybe just light showers) that are making it to the ground.

If you are on an IFR flight plan and heading straight for one of these do you ask for a deviation from ATC or do you just take the bumps inside the cloud? This assumes I don't have weather radar on board. One thing I am wondering is at what point does this become a cloud that you don't want to fly through?

At what point does ATC start vectoring you around this stuff? Is it when it is showing as a yellow return on the radar?

I would also like to hear any good stories about flying in this stuff.

Fly safe!
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By all means deviate around it. In a light airplane with no radar, I wouldn't go into any large building cumumlus. ATC is usually pretty good about deviations unless you're in the terminal area of a busy airport. The best way to go IFR in spring time thunderstorms is to stay in VMC. By the way, this is not just for general aviation. This is how most air carriers operate too.
So at what point does a cumulus cloud become a thunderstorm?

Do you also deviate around what looks like a smaller buildup? Say bases of 4000 and tops of 10000?
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So at what point does a cumulus cloud become a thunderstorm

When you see the lightening or hear the thunder...

Actually, a thunderstorm has three stages. The cumulus stage is the initial stage of thunderstorm development. This is when the updraft reaches the condensation point in the atmosphere and begins to form the cumulus cloud. During this stage, cumulus clouds can expand both vertically and laterally. In a short time the clouds can reach around 30,000 feet. Cumulus clouds may also merge together during this vertical development, creating a single cloud that can cover an area of 5 to 10 miles.

The mature stage begins when the first drop of precipitation from the cumulus clouds reaches the ground. In the convection cycle, this is when the water droplets become too heavy for the updraft to hold aloft.
During the mature stage, cloud tops begin to exceed 60,000 feet. Strong winds at these altitudes cause the tops of the clouds to level off, and take an anvil shape. The "anvil" is so high and temperatures are so low that the top of the cloud is composed entirely of ice crystals.
A thunderstorm is strongest toward the end of the mature stage. Rain will be the heaviest and lightning is abundant. This is when hail, strong winds and even tornadoes may form.

The dissipating stage is the end of a thunderstorm. This is when precipitation falls through the cloud, breaking it up. During the dissipating stage, the humidity in the air drops and the precipitation ends.

Hope this helps
Deviate around them! I developed this firm conviction on a flight to Islip NY last year. One time through a big developing cumulous cloud that was yellow inside was enough for me.
Where do you fly? Maybe Florida? If so, we seldom see the 'anvil top' usually associated with frontal storms. Our t'storms are generally caused by surface heating and the resulting sea breezes. They build straight up all day long and then come straight down, killing themselves off with downdrafts, in the afternoon. Thus, our storms usually don't last as long as say a storm associated with a squall line or a cold front. These storms feed themselves with moisture from the bottom, the upper level winds blow the tops ahead of the bottoms, and the downdrafts fall ahead of the bottom of the storm. Thus, the downdrafts don't necessarily kill off the updrafts and the storm can continue to build.

To answer your question...I agree with the previous post. Don't fly in the clouds at all if the radar is painting anything before you take off. Get a thorough preflight brief and update it with HIWAS or Flight Watch during the flight. Embedded t'storms are bad news in any a/c without radar. If the sky is clear around the buildups, by all means deviate...whether ATC OK's it or not. They usually will but you are the one who will have your wings ripped off so use that PIC decision making. Use 91.3 or cancel IFR if necessary. The trouble is that often times an overcast layer exists underneath the t'storms. If this is the case...do not fly. ATC is wonderful but we can't count on them to vector us around storms. At least I wouldn't bet my life on it.

My experiences...I don't have as many as most of the people on this site but I'll tell you what I have found. I'd like to hear theirs too. I have flown into some humongous buildups...the kind that go up to 30,000 or higher with those sharp, crispy edges, and cover a large area and found them to be as smooth as glass inside. I've also flown into fair weather cumulus that almost turned me upside down. I always, always stay away from the mature storms...the ones with precip blasting out of the bottom. My point is that you never know what you're gonna get so the safe bet is to stay away from the convective stuff.

Can anyone else comment on the building stuff? I've flown through it a lot and never had a bad experience, although I was usually pretty scared going in.

The worst experience I've had is the reason I advise you not to trust ATC to get you around the bad stuff. We were on the last leg of a long cross country. Stopped at VRB for dinner and a wx brief. Noticed a line of storms...yellow and orange with lots of green between the big cells. Considered staying the night but I thought we could make it safely (Mistake #1). My thinking was that ATC could easily get us through the line by vectoring us through the light stuff (mistake #2). This may have worked out except that ATC doesn't have discriminating radar in this area. I think they only show two levels with this type of radar as opposed to five levels with the more advanced radar. Someone help me out with the terms. Anyway, we ended up in some pretty severe embedded stuff that ATC was unable to help us out of. Mistake #3 was continuing the flight after being informed of their radar limitations. I include this story because I believe what we were flying through was building stuff. All updrafts...we gained 3000 ft in a C172 with the throttle at idle, indicating 100-140 kts. Sound like one of those chain of mistakes the NTSB always talks about? Well, we made it, no thanks to my stupidity. It was a learning experience I will never forget and am lucky to have lived through. Had those been downdrafts...
"I've flown through it a lot and never had a bad experience, although I was usually pretty scared going in."

I certainly wouldn't admit flying into TCu or TCb with anything but contrition. Especially not repeated times. The only people who need to be doing this are storm chasers and weather mod. Otherwise, stay well clear. If you've penetrated storms and building cumulus on numerous occasions, it's not a badge of honor, but luck. Be grateful that nothing serious has happened, but only admit to it in order to admonish others not to do something so unwise.

Reconsider spending a lot of time flying single engine IFR, too...aside from having one engine, most of the time you also have one vacum source, one electrical source, limited performance, and very few options.

Avoid flying in embedded conditions. Radar, or otherwise.

Even small storms can kill you.
Actually I fly in the NW around PDX. Listening to the ATIS today and such they are mentioning towering cumulus and cumulonimbus. All the commercial stuff looked like they were getting vectored around it. We don't get this kind of weather that much up here, so I don't have any experience flying in it.
Hey c172heavy, I fly a small turbo prop for a 121 carrier. We have a few cities that are so close to our hub that we fly between 4 and 9 thousand feet. We ALWAYS deviate from ANY buildup when possible. These are not necessarily TS but they are VERY uncomfortable for the passengers. They can also scare the passengers, especially in a light piston single. If the cloud is small enough in width you can get around it with only a few degrees turn and stay within one dot or so on the HSI or OBS then feel free to weave and bob, it can be kinda fun. (I know this is not in the Reg's but it does no harm and helps to keep the freq. open) If they are a little bigger then ask for a deviation from ATC as suggested before and 99% of the time you will get it. No matter what size plane you are in, always try and keep you passengers comfortable. -Bean
Thanks for the advice avbug. I guess I shouldn't say lots of times but rather a few times. All but one of these was as a student, not that that's much of an excuse. Also, in every case, ATC assured us that they were painting nothing on the radar. I guess my point was that radar doesn't show everything, especially the building stuff. ATC is also less likely to accomodate your request for a deviation if they show nothing, thus my recommendation to use PIC authority if they don't. I also wanted to express my surprise, and apparently my luck, that it wasn't worse inside those things. I certainly do not recommend flying into it.

My other intent was to get some advice from more experienced guys as to whether it usually is worse inside the towering stuff. Thanks for the input.

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