Small Transport; Low Wing; 2 Turboprop Eng
Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 150; Flight Crew Total 4200; Flight Crew Type 1300
Communication Breakdown; Confusion
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural FAR; Inflight Event / Encounter VFR In IMC
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification
Human Factors; Weather
Was IFR enroute to OTH on V287. Received ATIS information which indicated 10SM vis few clouds at 300 ft and 6000 ft broken. Advised Seattle Center I had the weather. They said they had planned on trying to get me in on the visual but the tower had said it might be too cloudy so they cleared me for the ILS approach via the OTH VOR.As I approached the VOR and descended to 5000 ft I got the west portion of the field in sight including runway 31. I advised Center I had the field in sight and requested a visual approach. Center cleared me for the visual approach and handed me off to North Bend tower. I contacted tower as I began my descent and maneuvered for runway 31.  The tower did not have me in sight and they were confused as to where I was; what runway I was planning; and how I was entering the pattern. The approach end of runway 31 was clear but the tower was under a cloud so they could not see me. I said I was over the VOR on a visual approach for 31; to which they responded by asking me to report a left base for 13. I clarified that I was right base 31; they replied that from over the VOR it would be left traffic for 13. I further clarified that I had 31 in sight and was on a visual for 31.During this time I was rapidly approaching the airport and was now on a 1 mile final for 31. There was a further very fast back and forth between myself and the tower that I cannot completely recall but they ended by quickly reading off the current weather conditions and clearing me to land on runway 31. At the time I was on short final and very focused on flying and landing the plane and was only thinking of listening for my landing clearance; which I read back and then landed. I heard the visibility as '10' the numbers '600' and '6000' for the sky conditions; and assumed since the ATIS had been 300 ft few and 6000 ft broken that it was now 600 ft few with a 6000 ft ceiling. This matched what I was seeing as descending through 1000 ft I was well below the clouds and had the entire field in sight.After shutting down I realized I wasn't entirely sure what I'd heard in that very fast-paced moment and checked the weather on my phone. I saw that just a few minutes before landing the skies had become '600 broken' and '6000' overcast and that the 600 ft broken ceiling meant I shouldn't have landed off the visual approach. A few minutes after I landed a new ATIS came out reflecting the lower ceiling.
Single engine aircraft pilot landed in marginal VFR conditions at OTH.