GULFSTREAM II CAPT RPTS EXCEEDING ACFT MAX SVC CEILING DUE TO WX AVOIDANCE.

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WE WERE FLYING A GII-SP FROM PHL TO LAS. WE HAD STARTED OUT AT FL390; THEN AS WE BURNED OFF FUEL WE REQUESTED WRONG WAY FL410. AS WE BURNED OFF MORE FUEL WE COULD HAVE CLBED TO FL430 BUT DID NOT AT THAT TIME THEN WHEN WE WERE N OF SALINA; KS; WE OBSERVED A LINE OF TSTMS VISUALLY AND ON OUR RADAR. SINCE THE MOON WAS VERY BRIGHT WE WERE ABLE TO VISUALLY OBSERVE THE CLOUDS. MY COPLT WAS WATCHING THE RADAR AND I WAS WATCHING OUTSIDE. WHEN IT BECAME APPARENT WE WERE NOT GOING TO TOP THE TSTM AHEAD OF US WE REQUESTED FL450; THE CERTIFIED CEILING OF THE AIRPLANE; AS WE GOT CLOSER TO THE STORM IT APPEARED WE WOULD BE ABLE TO TOP EVERYTHING IF WE TOOK A SLIGHT DEV TO THE R OFF COURSE. WE REQUESTED A R DEV AND WERE GRANTED SAME BY CTR; AND WERE GIVEN DIRECT BCE WHEN ABLE. AS WE BEGAN FLYING THROUGH WHAT APPEARED TO BE A 'SOFT AREA' ON THE RADAR AND A LOW PART VISUALLY; WE SUDDENLY WERE INTO THE CLOUDS. THERE WAS TURB AND LIGHTNING AND I ASKED MY COPLT TO REQUEST FL470; AND WERE GIVEN THE BLOCK OF FL450 TO FL480. WE CLBED TO FL476 AND ASKED CTR HOW THE OTHER ACFT HAD BEEN GETTING THROUGH THIS AREA. WE WERE TOLD THAT A HEADING OF 360 DEGS SHOULD GET US OUT OF IT IN SHORT ORDER. WE TURNED TO THE HEADING AND WERE OUT OF THE WX WITHIN A COUPLE OF MINS. WE THEN DSNDED TO FL430 AND RESUMED THE FLT. WHEN WE TOLD THE PAX WHAT HAD HAPPENED THEY DID NOT SEEM ALARMED AND ONE HAD NOT EVEN AWAKENED DURING THE TIME WE WERE IN THE CLOUDS WHILE ANOTHER SAID 'IT WAS NO BIG DEAL.' I BELIEVE THE VISUAL CUES THAT WERE GIVEN UNDER THE LIGHT OF THE MOON GAVE US A FALSE SENSE OF SECURITY. IN THE FUTURE I WILL MAKE SURE TO ASK FOR CTR'S ADVICE WHEN THE FIRST SIGN OF A LINE OF TSTMS SHOWS UP ON THE RADAR SCREEN. I WILL EVALUATE THE INFO THEY GIVE ALONG WITH WHAT IS OBSERVED ON THE RADAR AND WILL MAKE SURE TO AVOID IT BY AT LEAST THE RULE OF THUMB OF 10% HORIZ DISTANCE FOR THE CRUISE FLT LEVEL. THIS EVENT WAS RPTED TO OUR MAINT PEOPLE AND TO OUR COMPANY.