after picking up the stranded, hypothermic snowmobiler at a remote rescue location in dark night conditions, the pilot, who was wearing night vision goggles during the flight, encountered IMC in snow showers within a few minutes of departure. Although the pilot was highly experienced with SAR missions, he was flying a helicopter that was not equipped or certified for flight under IFR. The pilot was not IFR current, had very little helicopter IFR experience, and had no recent inadvertent IMC training. Therefore, conducting the flight under IFR was not an option, and conducting the night flight under VFR in the vicinity of forecast IFR conditions presented high risks. After the helicopter encountered IMC, the pilot became spatially disoriented and lost control of the helicopter