Cessna 340/340A
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 15; Flight Crew Total 3400; Flight Crew Type 50
Situational Awareness
Inflight Event / Encounter VFR In IMC; Inflight Event / Encounter Weather / Turbulence
Flight Crew Requested ATC Assistance / Clarification
Human Factors; Weather
Planning to ferry the airplane from TRK to another airport at a lower altitude in anticipation of IMC and extensive snow accumulation the next day; I checked weather and conditions at TRK (CAVOK) and in the Sacramento area (broken 3;000) I decided to attempt to fly VFR westbound along HWY 80. After departure TRK; I leveled off at 7;000 feet (>1;000 feet AGL) and followed HWY 80. After a few minutes of flight; the cloud layer on the other side of Donner Pass came into view. I decided to attempt fly underneath the clouds and descended to an altitude below the clouds. Approaching the highest elevation point of HWY 80; I determined there was not enough clearance over the pass and turned around. After turning around; I noticed a higher ceiling and better visibility over the old Donner Pass road and proceeded in that direction. After crossing Donner Pass at low altitude AGL; but clear of clouds; I started to realize that the ceiling was decreasing rapidly on the west side of the pass and I needed to take evasive action. Faced with the option of turning around at low altitude and cross the pass again in climb eastbound or climbing through the relatively thin layer of clouds; I elected to execute a maximum performance climb straight ahead in direction of the road and HWY through the clouds to a safe altitude and VMC where I contacted ATC and requested a clearance to complete the ferry flight IFR. My mistake was decision-making that relied on interpolating weather conditions in between two points that are too far apart and with too many weather-influencing factors. I was surprised by the sudden onset of low and descending ceiling after taking off in CAVOK minutes earlier. I should have never attempted to execute the flight VFR. Easily accessible additional real-time weather information for geographic locations between airports would have been helpful and could have resulted in better decision-making.
C340 pilot reported departing TRK in VFR conditions headed across Donner Pass westbound and encountered IMC conditions. Pilot climbed to VFR conditions and contacted ATC to complete the flight IFR.