An EC135 helicopter pilot wearing night vision goggles on an early morning departure; flew into IMC; which the goggles masked because he could see lights through the fog. After realizing his situation; he contacted Approach and was given clearance for an ILS at a nearby airport.

Narrative

We had just picked up our patient and were enroute. Weather for our destination was forecasted as follows: ZZZ XX0853Z AUTO 00000KT 8SM SCT008 OVC041. The ATIS was reporting a ceiling of 1;400 FT with 7 miles visibility. We departed in the dark; still early morning; local and approximately 10 miles south of our destination. Ten minutes later the weather began to deteriorate and I could no longer see ground lights with the goggles. I looked to my left and could still see ground lights so I began a left hand turn back to the south. Once heading south we notified company that we would not be able to go to scheduled hospital and that we were diverting. I continued heading south until I could see ground lights again. I attempted to descend so I could go below the ceiling but when I reached 700 FT AGL I realized that that was not possible. I then began a climb to 2;800 FT and called Approach and declared IMC and requested vectors to VMC conditions. Approach notified me that they currently did not show any VMC conditions in my area. I then requested vectors for the ILS at a nearby airport. Approach began vectoring me for the ILS Runway 16. Approximately 12 miles from the airport; we broke out and I canceled my IFR clearance and made a visual approach without incident. Be careful flying with night vision goggles when weather can be a possible issue because the goggles will allow you to see through clouds up to a certain point. Ensure you look out from under the goggles as a cross reference if there is a question about visibility.