A B737 FLC OVERSHOT THEIR ASSIGNED ALT AT FUTON WHILE ON A HOLDING CLRNC WITH TSTMS IN THE AREA AND VERY BUSY. THEY WERE DISTR WHEN THE FLT ATTENDANT CAME IN TO THE COCKPIT TO CHK ON PAX CONNECTIONS. THEY FAILED TO SET THE LCL QNH IN THEIR ALTIMETERS SINCE THE CHKLIST WAS NOT COMPLETED.

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INBOUND TO MSP ON SKETR 1 ARR; TSTMS ALL AROUND. A SEVERE SQUALL LINE WAS PASSING THROUGH MINNEAPOLIS AREA AT THE TIME. JUST W OF SKETR INTXN; APCH CTL ADVISED THAT MSP ARPT WAS CLOSED DUE TO 'SEVERAL ACFT WITH MAJOR HAIL DAMAGE ON RWYS; NEEDED TO BE TOWED OFF.' WE WERE INITIALLY GIVEN HOLDING INSTRUCTIONS TO STANDARD DEPICTED HOLDING SW; AT SKETR; L TURNS; FL240. IT BECAME APPARENT WE WOULD BE UNABLE TO HOLD AT SKETR DUE TO TSTMS IN AREA. WE; AS WELL AS SEVERAL OTHER ACFT; ASKED TO HOLD AT SHONN; TO THE E OF SKETR. WE WERE CLRED TO SHONN TO HOLD; DSND TO FL190. SHONN WAS ALSO IN THE WX AND WE REQUESTED; AND WERE CLRED TO FUTON TO HOLD 17000 FT; AND WERE LATER CLRED TO 14000 FT. MEANWHILE; WE WERE CHKING FUEL; ALTERNATE WX; TALKING TO COMPANY DISPATCHER; ETC. I WAS FLYING AND TALKING TO ATC; WHILE COPLT TALKED TO COMPANY; GOT UPDATED WX FOR MSP AND ALTERNATES; AND MADE PAX ANNOUNCEMENT. FLT ATTENDANT CAME UP TO ASK ABOUT CONNECTIONS; ETC. I ADVISED HER THAT WE WERE VERY BUSY AND THAT WE WOULD GET MORE INFO TO HER AND PAX WHEN WE HAD TIME. SHE WAS A BIT PERSISTENT AND I WAS TRYING TO POLITELY; BUT FIRMLY; GET HER OUT OF THE COCKPIT. SHORTLY AFTER LEVELING OFF AT 14000 FT; THE APCH CTLR CALLED TO SAY THAT WE APPEARED TO BE AROUND 400 FT LOW. WITH EVERYTHING ELSE GOING ON WE NEGLECTED TO FINISH DSCNT CHKLIST; WHICH WAS STARTED SEVERAL TIMES. ALTIMETER WAS 29.47 VERSUS 29.92; WHICH WAS STILL SET. WE IMMEDIATELY CORRECTED ALTIMETERS AND ALT. CTLR SAID THAT IT WAS 'NOT A PROB;' NO TFC CONFLICTS. THIS WAS A 'CLASSIC' SIT. WE EVEN HAD A JUMP SEAT RIDER (COMPANY PLT); WHO WAS TRYING TO ASSIST; BUT WITH THE FLT ATTENDANT LEANING OVER HIS SHOULDER HE DID NOT CATCH THE ALT SIT RIGHT AWAY EITHER. HE SAID HE HAD JUST NOTICED AND WAS TRYING TO TELL US ABOUT THE ALT WHEN ATC CALLED. OUR COCKPIT WORKLOAD WAS MAX DURING THIS TIME AND WE WERE OBVIOUSLY NOT ABLE TO DEAL WITH ADDITIONAL DISTRS OF ANY KIND. WE WERE WORKING WELL TOGETHER; BUT IT WAS NOT WELL ENOUGH TO PREVENT THE RESULTING ALT SIT. IN THE FUTURE; I WILL BE MORE FIRM ABOUT COMPLETING CHKLISTS IN A TIMELY MANNER; DESPITE INTERRUPTIONS. AND I AM WORKING UP NEW BRIEFING AND RESOURCE TECHNIQUES TO PREVENT ADDITIONAL DISTRS; SUCH AS PERSISTENT FLT ATTENDANTS; FROM INCREASING THE WORKLOAD TO THE DETRIMENT OF SAFETY.