ATX HELI ENTERS IMC AFTER DSNDING TO AVOID. DECLARES EMER; REQUESTED ASR APCH.

Narrative

WHILE RETURNING TO MY BASE FROM AN OFFSHORE LOCATION IN PREDOMINANT VMC (1000-1500 FT OVCST; 5-7 MI VISIBILITY; SCATTERED RAIN SHOWERS). I SUDDENLY ENCOUNTERED FOG. I DSNDED FROM 500 FT MSL TO 300 FT MSL; THEN MOMENTARILY TO 200 FT MSL IN AN ATTEMPT TO GET BENEATH WHAT I THOUGHT WAS A SHALLOW STRATUS LAYER. I NEXT ATTEMPTED A 180 DEG CLBING TURN BUT FOUND MYSELF ABOVE 300 FT MSL IN SOLID OVCST APPROX 2.8 NM FROM MY LORAN INDICATED DEST. WITHIN THE PRECEDING 15 MINS; 3 COMPANY ACFT HAD DEPARTED THE SAME GENERAL AREA IN VMC. I WAS SURPRISED BY THE RAPID CHANGE IN FLT CONDITIONS. COMPANY ACFT TO MY NE WERE RPTING CEILINGS OF 1300-1500 FT MSL. I CONTINUED MY OUTBOUND CLB TO 1500 FT MSL WITHOUT BREAKING OUT -- AT THAT POINT; I DECLARED AN EMER TO CORPUS CHRISTI APCH CTL AND REQUESTED AN ASR APCH INTO CORPUS CHRISTI NAVAL AIR STATION. I WAS GIVEN AN ASR APCH TO VMC (400 FT MSL) WHERE I RESUMED VFR FLT TO MY DEST. I WAS IN AN AREA OF RAPIDLY CHANGING METEOROLOGICAL CONDITIONS FOR WHICH I WAS UNPREPARED (BASED UPON FORECASTS; INFLT OBSERVATION AND EXPECTED CONDITIONS). HAD I REACTED 30 SECONDS TO 1 MIN EARLIER; IT IS POSSIBLE I WOULD HAVE REGAINED VMC CONDITIONS. AT THE POINT THAT I DECLARED AN EMER TO ATC; I WAS EXERCISING WHAT I CONSIDERED TO BE MY LAST AVAILABLE OPTION.