SMA VFR TKOF ENTERED IMC.

Narrative

A FOG BANK MOVED OVER THE DEP END OF RWY 29 AT PRESCOTT ARPT. THE TWR HAD DECLARED RWY 29 THE ACTIVE AND I OBSERVED NUMEROUS ACFT (SMALL; GA) TAKING OFF AND FLYING INTO THE FOG. AT FIRST I COULD NOT BELIEVE MY EYES AND THOUGHT THE PLTS WERE CRAZY AS THE ACFT INVOLVED ARE KNOWN TO ME AND ARE NOT EQUIPPED FOR FLT IN IMC. I WATCHED THIS OCCUR REPEATEDLY FOR APPROX 20 MINS AS I PREPARED TO DEPART IN MY ACFT ON AN ACTUAL SEARCH MISSION FOR A DOWNED ACFT. I CALLED GND CTL AND REQUESTED TO USE RWY 11 TO AVOID FLYING INTO THE FOG. MY REQUEST WAS DENIED. I WAS TOLD TO TAXI TO RWY 29. AFTER RUNUP; I REQUESTED (FROM THE LCL CTLR) CLRNC FOR AN IMMEDIATE L TURN OUT TO AVOID THE FOG. AGAIN; MY REQUEST WAS DENIED. BY NOW THE FOG HAD MOVED TO ALMOST MID-FIELD. THE DEP IN FRONT OF ME WAS CLRED TO TKOF; AND I WATCHED HIM DISAPPEAR INTO THE FOG. THEN I WAS CLRED FOR TKOF AND TOLD THAT I WAS TO 'FLY RWY HEADING AND TWR WOULD CALL MY TURNOUT.' I ENTERED THE FOG AT ROTATION AND PROCEEDED WITH AN INST TKOF BREAKING OUT AT APPROX 700 FT AGL. IN 32 YRS OF PROFESSIONAL FLYING; THIS IS THE MOST INCREDIBLE EXPERIENCE EVER. IN RETROSPECT; I SHOULD HAVE REFUSED TO TKOF. THE TWR WAS PROBABLY ILLEGAL IN EXTREME AND CRAZY ON TOP OF IT.