Bell 206 pilot reports encountering intense rain and turbulence resulting in inadvertent climb and unusual attitudes. When control is regained and VMC encountered the pilot elects to land in a field and wait for the storm to pass.

Narrative

The mission was to transport two offshore platform operators from the airport to the platform and pick up two operators to transport back to the airport; normally a 25 minute one way flight. A cold front trough was moving into the area. Pilot checked TAF; METAR; and radar NEXRAD images from National Weather Service to ensure sufficient time would be available to make the round trip and after embarking the passengers we took off. The outbound flight took about 5 minutes longer than usual and the helicopter also visited a satellite platform at operator request; which took an additional 9 minutes. After embarking the two returning personnel the helicopter departed the offshore platform for the airport; cruising between 400 and 1;000 FT MSL. Approximately 18 miles south southeast of the airport visibility started to decrease due to rain and fog obscuration of the western shore; the intended route to the airport. Pilot had already obtained ATIS and contacted the airport Tower to check for any inbound traffic and then Approach for a special VFR clearance; which was issued with a transponder code. While this was happening pilot-in-command was turning further east of course experiencing instinctive reluctance to turn towards the approaching weather and encountering increasing turbulence and rain while maintaining visual contact with the surface of the bay. Next the aircraft encountered some intense rain and an updraft that took the helicopter to 3;000 FT MSL. Visual contact with surface was lost. During this sequence of events aircraft angle of bank reached 30 degrees right and experienced an airspeed range of zero to 130 KTS indicated airspeed; requiring an unusual attitude recovery. Pilot advised Approach Control that we were descending to below 1;700 FT MSL as per original clearance. We were advised that we were east of the airport and to switch to Tower. On contacting Tower we were again advised we were well east of the airport and pilot-in-command requested ASR assistance while still heading northeast due to nasty weather pushing in from the west. Tower switched us back to Approach Control; who again advised us that we were well east. By this time the pilot-in-command regained good visual ground reference at 400 FT MSL and elected to land at this location in a pasture. It was impossible to communicate on the radio with Approach or Company Dispatchers to advise them of the safe landing. While shutting down the helicopter; the pilot contacted Company Dispatch on his cell phone to report being safely on the ground and requested they advise the airport Tower and Approach Control. He then secured the helicopter and contacted the other pilot at his base to report safe.