Narrative:

I received a flight weather briefing for my intended route. Bases were forecast to be 7;500 to 8;000 ft and scattered thunderstorms. I was en route climbing and I made a decision to climb over a section of cloud cover that was next to some building cumulus clouds. I commenced climbing and thought I would be over it by 11;000 ft. This put me in close proximity to [a restricted area]; that I was avoiding since I knew it was 'hot' up to 15;000 ft. I was then in an air mass that was building and taking me up higher and I was climbing to stay clear of the clouds. I attempted to turn around and made a 360 degree turn and found that where I had entered was now higher then the original flight path. I was now in a narrow canyon of clouds and to stay clear of them I was forced even higher. I was trying to get my oxygen system working and I was really worried about getting in to the clouds because every time I got close to them it was really turbulent. I was not talking to ATC for flight following and I did not have the frequency available to call for a clearance and I was afraid to look down into the cockpit to find it on my charts should I inadvertently go into the clouds. I topped out at around 19;000 ft and then started to descend out of this area. I was too embarrassed to call ATC for help once I cleared the area. This was a foolish decision since I should have been on flight following the entire route and should have never been in this situation. I was surprised to find that the forecast was not as I expected with scattered thunderstorms; just this one big cell/air mass on my intended flight path. I placed too much emphasis on the ability of the aircraft to climb fast enough to get me over it and underestimated the ability of the clouds to build so fast. [This was] very poor decision making.

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Original NASA ASRS Text

Title: M-20K pilot; expecting only scattered thunderstorms on a VFR flight; encountered fast-building cells which he was unable to avoid by a 180-degree turn and was barley able to avoid by climbing to FL190. Pilot made no contact with ATC.

Narrative: I received a flight weather briefing for my intended route. Bases were forecast to be 7;500 to 8;000 FT and scattered thunderstorms. I was en route climbing and I made a decision to climb over a section of cloud cover that was next to some building cumulus clouds. I commenced climbing and thought I would be over it by 11;000 FT. This put me in close proximity to [a restricted area]; that I was avoiding since I knew it was 'hot' up to 15;000 FT. I was then in an air mass that was building and taking me up higher and I was climbing to stay clear of the clouds. I attempted to turn around and made a 360 degree turn and found that where I had entered was now higher then the original flight path. I was now in a narrow canyon of clouds and to stay clear of them I was forced even higher. I was trying to get my oxygen system working and I was really worried about getting in to the clouds because every time I got close to them it was really turbulent. I was not talking to ATC for flight following and I did not have the frequency available to call for a clearance and I was afraid to look down into the cockpit to find it on my charts should I inadvertently go into the clouds. I topped out at around 19;000 FT and then started to descend out of this area. I was too embarrassed to call ATC for help once I cleared the area. This was a foolish decision since I should have been on flight following the entire route and should have never been in this situation. I was surprised to find that the forecast was not as I expected with scattered thunderstorms; just this one big cell/air mass on my intended flight path. I placed too much emphasis on the ability of the aircraft to climb fast enough to get me over it and underestimated the ability of the clouds to build so fast. [This was] very poor decision making.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.