ALT OVERSHOT WHEN AUTOPLT FAILED TO CAPTURE ALT.

Narrative

THE PROB AROSE WHEN WE TOOK A LIGHTNING STRIKE AS WE APCHED OUR 7000 FT CLB/XING RESTRICTION DURING OUR CLB TO 17000 FT. NUMEROUS TSTM CELLS; (RED ON RADAR); DIRECTLY ACROSS AND ALONG OUR RTE DICTATED THE USE OF AUTOPLT AND FMS. THIS WAS EMPLOYED AT 2000 FT AGL SO WE COULD PICK OUR WAY THROUGH THE WX. RADIO TFC WAS VERY HVY AND AS DISTRACTING AS THE LIGHTNING FLASHES. I FAILED TO NOTICE THAT THE FMC MEMORY HAD BEEN COMPROMISED BY THE LIGHTNING STRIKE UNTIL DEPARTURE CTL ASKED US TO VERIFY ALT. I IMMEDIATELY STOPPED OUR CLB; BUT WAS THEN CLRED TO CONTINUE OUR CLB UNRESTRICTED TO 17000 FT. THIS WAS OUR FIRST ACTUAL COM FROM DEP CTL AFTER TKOF. CONTRIBUTING FACTORS STARTED THAT MORNING WITH A RETURN TO GATE TO EJECT A PROB PAX; NUMEROUS DELAYS DURING THE DAY; SEVERE WX AT NIGHT; DIVERSIONS FROM SIDS AND STARS FOR WX AVOIDANCE; VERY HVY RADIO TFC; A VERY LONG DUTY DAY AND FACING A MINIMUM CREW REST. SIGNIFICANT IN THIS AND SIMILAR SITS IS THE FACT THAT CTLRS SEEM TO BE WORKING TOO MANY FREQS AND SECTORS AT NIGHT; BOTH IN THE TWR AND IN DEP AND APCH. WHEN YOU CANNOT COMMUNICATE YOUR DILEMMA; I.E.; WX OR LIGHTNING STRIKES; STRESS IMPAIRS PERFORMANCE AND WHEN COUPLED WITH PROGRAM OR SYS FAILURE CAUSES UNACCEPTABLE EXCURSIONS.