DEADHEADING CREW MEMBER REPORTS ICE FORMING AND SHEDDING ON THE WING UPPER SURFACE OF B737NG DURING CLIMB OUT.

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COMMUTING ON FLIGHT #; SITTING IN ROW 18 CAPTAIN SIDE (JUST AFT OF THE LEFT WING). METAR XA56Z 310/11 8SM 18BKN 24BKN 60OVC 01/M03 30.23 METAR XB25Z 330/10 8SM 18SCT 60OVC 00/MO3 30.24 AFTER PUSHBACK THE ACFT WAS DEICED FOR COLD SOAKED FUEL FROST UNDER THE WING. I VISUALLY CHECKED THE TOP OF THE WING FOR ICE OR PRECIPITATION AND SAW NONE. TAKEOFF WAS NORMAL; CLIMBING THRU BKN/OVC 2K-10K WITH LAYERS ABOVE 10000 FT. ON CLIMBOUT (APPROX 6000 FT) HEARD AND FELT A SERIES OF BANGS BELOW MY FEET (LEFT SIDE OF ACFT). ASSUMED IT WAS BAGS OR CARGO SHIFTING IN THE AFT CARGO COMPARTMENT. AFTER LEVELING AT CRUISE (APPROX 5 MINUTES AT CRUISE) HEARD A SERIES OF BANGS FROM THE RIGHT SIDE OF THE ACFT. NUMEROUS PAX HEARD THE NOISE AND SAID THEY SAW SOMETHING DEPART THE WING AREA. I CALLED THE COCKPIT VIA THE AFT FLT ATTENDANT INTERPHONE. SPOKE WITH CAPTAIN/FIRST OFFICER ABOUT WHAT I OBSERVED. I SPECULATED IT WAS ICE THAT FORMED ON THE WING ROOT (REFERRING TO THE RBF). THERE WERE NO ABNORMAL INDICATIONS FROM THE CABIN AND THE CAPTAIN REPORTED NO ABNORMAL INDICATIONS OR HANDLING. ON DESCENT I OBSERVED A LARGE AREA OF CLEAR ICE (OVER 1/4 INCH THICK) ON THE WINGS (LEFT AND RIGHT). THE ICE HAD FORMED FROM THE WHITE WALKING AREA NEAR THE WING ROOT; OUTWARD APPROX 6 FT; WHERE THE SHEET OF ICE HAD BROKEN AND SHED WAS EASILY OBSERVABLE. THE ICE HAD FORMED OVER THE FUEL TANK OUTLINE (BLACK LINE) ON THE UPPER SURFACE OF THE WING. ON THE GROUND I SPOKE WITH THE CAPTAIN AND FO ABOUT THE INCIDENT. BOTH THE CAPT AND I SPOKE WITH CHIEF PLT ABOUT THE INCIDENT. THE MOST IMPORTANT ISSUE HERE IS THAT THERE WAS NO ICE OR PRECIPITATION ON THE UPPER SURFACE OF THE WING PRIOR TO DEPARTURE. THE FO HAD EVEN USED A LADDER DURING PREFLIGHT TO CHECK THE UPPER SURFACE OF THE WINGS. MY ASSUMPTION IS THAT THE FUEL TANK TEMPERATURE WAS NEAR FREEZING AND AS THE ACFT CLIMBED THRU THE MOIST LAYERS; ICE FORMED OVER THE COLD SOAKED FUEL TANKS. ANTI-ICING ON THE GROUND WOULD NOT HAVE STOPPED THIS FROM OCCURRING.SUPPLEMENTAL INFO FROM ACN 815790: THIS FLIGHT WAS AN AM ORGINATOR. DURING HIS PREFLIGHT WALK AROUND INSPECTION; THE FO DISCOVERED ICE HAD FORMED ON THE UNDERSIDE OF BOTH WINGS. DURING THE EXTERIOR INSPECTION HE USED A BAGGAGE LOADER TO GET A CLOSER VIEW OF THE UPPER SURFACE OF THE WINGS. HE DID NOT FIND ANY EVIDENCE OF CONTAMINATION ON THE UPPER SURFACES OF THE WINGS. AS PART OF MY PREFLIGHT I WENT TO THE AFT GALLEY AREA; OPENED BOTH EXIT DOORS TO GET A CLOSER LOOK AT THE STAB AND TAIL AREA; AND FOUND NO CONTAMINATION ON THOSE SURFACES. AFTER THE EXTERIOR INSPECTIONS; WE COORDINATED WITH GROUND CREW FOR DEICING THE UNDERSIDE OF BOTH WINGS. THE DEICING CREW ALSO LOOKED AT THE WINGS BEFORE PUSHBACK TO MAKE SURE THEY WOULD BE ABLE TO REMOVE ALL THE ICING. DURING THE REST OF THE PREFLIGHT I NOTED THE FUEL TEMPERATURE WAS -2 DEGREES CELSIUS. THE ATIS WEATHER REPORT WAS: WINDS 310/11; VISIBILITY 8SM; CEILING 1800 FT; TEMPERATURE +1 CELSIUS; DEW POINT -3 CELSIUS; ALTIMETER 30.23. AIRPORT SURFACES WERE WET DUE TO AN EARLIER FRONTAL PASSAGE BUT NO PRECIPITATION WAS FALLING AT THE TIME. PUSHBACK; DEICING; TAXI; AND TAKEOFF WERE UNEVENTFUL. ON CLIMBOUT WE PASSED THROUGH BROKEN DECKS AT 1800 FT AND 2400 FT MSL. WE THEN CLIMBED THROUGH AN OVERCAST DECK AT 6000 FT MSL AND EXITED AROUND 8000 FT MSL. DURING THE REST OF THE CLIMB TO FL220 WE PASSED THROUGH A FEW THIN CLOUD LAYERS. AT FL220 AND THROUGH THE REST OF THE FLIGHT WE REMAINED IN VFR CONDITIONS WITH ONLY A FEW AREAS OF LIGHT HAZE. ENGINE ANTI-ICE WAS USED FOR MOST OF THE CLIMBOUT. AS WE LEVELED OFF; A COMPANY JUMPSEATING PILOT CALLED THE COCKPIT AND STATED THAT JUST AFTER THE 10000 FT HE AND SOME PAX HEARD A NOISE THAT SOUNDED LIKE SOMETHING BOUNCING OFF THE SIDE OF THE FUSELAGE. THE JUMPSEATING PILOT SAID AT FIRST HE THOUGHT THE NOISE WAS CAUSED BY BAGGAGE SHIFTING IN THE CARGO BAY; BUT HE AND ANOTHER PAX NOTICED A FLASH OF LIGHT OUTSIDE ONE OF THE WINDOWS. THE JUMPSEATING PILOT THEN LOOKED AT THE TOP OF THE WINGS AND NOTICED T