ACR LGT WITH SHATTERED WINDSHIELD MAKES PRECAUTIONARY LNDG AT NEAREST ARPT.

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CRUISING AT FL390 COPLT'S FRONT WINDOW SUDDENLY SHATTERED AND BEGAN ARCING (ELECTRICALLY). CAPT NOTICED WINDOW VISIBLY BOWING INWARD. CAPT FLEW ACFT AND COPLT COMMUNICATED WITH CENTER AND ATC. CAPT DECIDED TO LAND AT SPOKANE; DOUBTING INTEGRITY OF SHATTERED WINDOW. COPLT RELAYED INTENTIONS TO ATC AND COMPANY. AND; WITH APPROVAL FROM BOTH; BEGAN DSCNT. BOTH PLTS DONNED O2. SHATTERED WINDOW PROC WAS EXECUTED FROM MANUAL AND PAX SEATBELT SIGN ILLUMINATED. CAPT INFORMED PAX AND CABIN CREW VIA PAX ANNOUNCEMENT AS TO PROB AND OUR INTENTIONS TO LAND AT SPOKANE. VISUAL APCH AND LNDG EXECUTED W/O FURTHER INCIDENT. UPON VISUAL INSPECTION OF WINDOW; THERE APPEARED TO BE A CENTRAL POINT OF ORIGIN OR IMPACT FROM WHICH EXTERIOR PIECES OF GLASS WERE MISSING AND ALL CRACKS EMMINATED. WE DO NOT KNOW WHETHER SOMETHING IMPACTED WINDOW; BUT CONSIDER IT A REMOTE POSSIBILITY. HAVE HEARD OF RARE INSTANCES OF BIRDS AT HIGH ALTS OR PERHAPS WX BALLOON. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATED THAT MANUAL ONLY HAS PROC THAT CALLS FOR TURNING OFF WINDSHIELD HEAT. MANUFACTURER MAINTAINS OUTER PANE CRACKING OR SHATTERING DOES NOT AFFECT STRUCTURAL INTEGRITY; BUT IN THIS CASE WAS A BROWN STREAK IN MIDDLE OF INNER PANE AND INWARD BOWING; WHICH SEEMED UNUSUAL WITH PRESSURIZATION; SO PIC ELECTED TO LAND AT NEAREST SUITABLE. DID NOT NOTICE IF BOWING DECREASED AS SPEED AND ALT AND PRESSURIZATION CHANGED. FAA INSPECTOR WAS ON SCENE AT ARR AND INSPECTED WINDSHIELD AND WAS SATISFIED WITH FLT CREW ACTION. DID NOT SEE ANYTHING STRIKE WINDSHIELD BUT HEARD A POP WHICH COULD HAVE BEEN A STRIKE OR JUST FROM THE GLASS STARTING TO SHATTER.