Narrative:

While in cruise flight; it became necessary to deviate due to existing and building thunderstorms. ATC had advised me of the largest storm which I had a visual on and was on a westerly vector along the coast. The storm was to the north. I was also using xm downloaded weather for information. When the xm indicated it was safe to turn more northerly towards cew; I advised ATC that I was starting my turn and he agreed that the turn looked 'good to him'. I went IMC momentarily and when I broke out there was a large buildup at my twelve o'clock position. The main storm was still off to my right. I could see several breaks around the buildup and requested and was approved for a climb to 10000' in an attempt to remain visual on the buildup. I was unable to do so and encountered IMC. While IMC; I flew into a fast building area of weather that was joining up with the known cell to my right. I advised ATC of my dilemma who was very surprised to see how quickly the cell was developing. He vectored me through the safest part of it. I was forced to use every method from my training by turning the autopilot off; slowing; and keeping the wings level. At one time with [climb power] I was descending at 1500 feet per minute. I eventually exited the weather and looked out my right rear window to see the huge storm that was developing behind me. ATC advised that it had completely closed up. Only then did the xm downloaded weather update to reflect the actual conditions that existed.later; I contacted a tv meteorologist friend and told him of my encounter. He assisted me in downloading archived radar images that showed how fast these air mass cells/thunderstorms were developing - and how close I came to being a statistic. I knew not to use the xm for penetration prevention and did so in error. I am very lucky that the outcome was good. The great guy at ATC was almost as nervous as I was. The delay of the update with the speed of the buildup of these air mass thunderstorms resulted in an inaccurate pictorial that I was using to determine my route of flight.

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Original NASA ASRS Text

Title: PA32 pilot reports entering a rapidly building thunderstorm while attempting to use XM Radar to navigate around; with ATC concurrence.

Narrative: While in cruise flight; it became necessary to deviate due to existing and building thunderstorms. ATC had advised me of the largest storm which I had a visual on and was on a westerly vector along the coast. The storm was to the north. I was also using XM downloaded weather for information. When the XM indicated it was safe to turn more northerly towards CEW; I advised ATC that I was starting my turn and he agreed that the turn looked 'good to him'. I went IMC momentarily and when I broke out there was a large buildup at my twelve o'clock position. The main storm was still off to my right. I could see several breaks around the buildup and requested and was approved for a climb to 10000' in an attempt to remain visual on the buildup. I was unable to do so and encountered IMC. While IMC; I flew into a fast building area of weather that was joining up with the known cell to my right. I advised ATC of my dilemma who was very surprised to see how quickly the cell was developing. He vectored me through the safest part of it. I was forced to use every method from my training by turning the autopilot off; slowing; and keeping the wings level. At one time with [climb power] I was descending at 1500 feet per minute. I eventually exited the weather and looked out my right rear window to see the huge storm that was developing behind me. ATC advised that it had completely closed up. Only then did the XM downloaded weather update to reflect the actual conditions that existed.Later; I contacted a TV meteorologist friend and told him of my encounter. He assisted me in downloading archived radar images that showed how fast these air mass cells/thunderstorms were developing - and how close I came to being a statistic. I knew not to use the XM for penetration prevention and did so in error. I am very lucky that the outcome was good. The great guy at ATC was almost as nervous as I was. The delay of the update with the speed of the buildup of these air mass thunderstorms resulted in an inaccurate pictorial that I was using to determine my route of flight.

Data retrieved from NASA's ASRS site as of April 2012 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.