Narrative:

Around xa:25 on [date]; my passenger and I departed ZZZ; bound for ZZZ1. My passenger was a friend; colleague; and [xx] hour student pilot; for whom this was the first cross-country experience in a small plane. Weather at our point of departure was clear. The departure from ZZZ and crossing of [mountain pass] were uneventful. At our destination; a front was forecast to come in around midday; bringing rain and lowered ceilings. Nevertheless; terminal forecasts near [destination area] were VFR; and we believed we would land before the front arrived at ZZZ1. When clouds are forecast for the [destination area] area; it is often possible to safely cross the [mountain range] by flying VFR under clouds on the west side; the east side is usually free of low cloud for most months of the year. I have done this a number of times; and I expected to be able to do something similar on this flight. Around ZZZ2 we got our first look at the west side weather. The clouds were dark; tall and forbidding; rags of fog were starting to form in some hollows around some peaks. The [enroute station] ASOS suddenly dropped from reporting ceilings of around 6;000' to 700'; the temperature/dew point spread was only two degrees. At xa:50 I called a diversion; and after a brief stop at ZZZ3; we went to ZZZ4 to take on fuel and consider our options. I briefed the weather at ZZZ4; and decided that the worst weather was to the north. My passenger independently looked at the weather; and came to the same conclusion. Terminal forecasts near our destination were 3;000 to 5;000'; 6+ miles visibility. There were no terminal forecasts along our route; so we relied on the gfa [graphical forecasts for aviation] tool; weather radar; and the windy app to build a picture of the intervening weather. Based on that; we expected to go under a layer of mid-level cloud west of the crest; but to be able to make the trip VFR. We decided on a [new] route south of [mountain]. We took off from ZZZ4 about xc:45; with unlimited visibility and only some high cloud. We climbed to 8;500 by about 10 miles east of [lake]. Around [lake]; we encountered a layer of cloud at our altitude; and descended to 6;500 by [mountain pass 1]. At [mountain pass 1]; I looked northwest along our intended route and saw the shoulders of [large mountain] were shrouded in cloud. Looking west along the valley I saw a bank of clouds at and below our level; but with an apparent path underneath. I decided to reroute us via ZZZ5; under the clouds. I descended to 3;300' by three miles west of ZZZ6; about xd:20. We were under a layer of smooth cloud but well clear of the cloud with plenty of visibility. A couple of minutes later; we flew into intense rain that dropped flight visibility to (I would estimate) three miles. A couple of minutes later; the rain eased off; but we were flying through mist; below ragged clouds with visibility varying between three and five miles. My passenger and I discussed the situation; and decided that this was probably a narrow band of bad weather associated with the front; and that we could continue carefully through it and come out in good weather on the other side. I switched the GTN750 in my panel to terrain mode; to back up our visual way finding; reduced power and put in flaps to slow the plane down. We were roughly ten miles west of ZZZ6. Over the next five or so minutes; we flew down the center of the valley; looking forward constantly to pick out the terrain and see if the weather was getting better or worse. We were also slowly descending; but I was not particularly conscious of that fact; as I was focused on looking out the windows. Around xd:30 we came over the east shore of [lake 1]; elevation 770'; we were 2 ;200'. I had to descend again to avoid low-hanging cloud. Flight visibility also started to reduce further; I would guess between one to two miles. I started to think that we should turn around; but figured we'd look around one more corner. As we turned around a bluff on the north shore of the lake; I saw a cloud in front of me; and before I could decide what action to take; flew right into it. I knew I had to execute a 180 as I had been taught in training; or we would likely die. My passenger said the same. I looked at the terrain map and chose a left turn; where there was much more room. I executed a standard rate turn to the left using instruments only; at about 2;000'. After about one and a half minutes in IMC we broke out on an eastbound heading. As we flew away from the lake; visibility improved slightly to about three miles and we climbed to 2;500'. Clouds were probably 200'-500' above us. My passenger and I discussed the situation; acknowledged that we were in an emergency; and that our overriding goal now was to land the plane such that we could walk away. We decided to try for ZZZ5; now about four miles north. I gave him my ipad; and told him to manage the GTN750 and brief me on the airport. At about xd:40 we found our path to ZZZ5 blocked by a wall of cloud; and we turned around; once again heading east up the valley from a point northeast of [lake 1]. We discussed emergency landing options; and whether we should attempt to fly back to ZZZ6; about 20 miles east. My passenger suggested ZZZ7; a charted private turf strip about five miles east of our position. I agreed that if the strip was usable for us; we would land. The strip looked to be in good condition; so I executed a straight-in landing to the east; touching down uneventfully at about xd:45. We were picked up by car from ZZZ7 about two hours later. During this time; the weather deteriorated further; with spells of heavy rain; and clouds descending further to cover the sides of the valley. In the few days since this incident; I have reflected extensively on what went wrong and what went right.what went wrong:I chose to continue into inclement and deteriorating weather amidst mountainous terrain. I think my judgment simply failed me in this case. I had diverted or rerouted two other times before that day due to weather; those calls were right; this one was wrong. I don't think I'll make this mistake again. I had a false; overly-optimistic mental picture of the weather; which fed into my choice to continue. I have had little experience flying in heavy rain; or in conditions of marginal visibility. I have flown about 180 hours of VMC; about 18 hours of simulated IMC; and two hours of actual IMC in clouds (with an instructor). I was blindsided by how rain can reduce visibility from unlimited to marginal in an instant. I didn't quite know what heavy rain looks like; now I do. I was distracted by the marginal weather and did not fully process the fact that we were slowly descending for several minutes between ZZZ6 and lake. We were being wedged in by clouds and terrain and it took a while to realize how wedged in we were. I should have disregarded the fact that my passenger; an even less experienced pilot than me; was comfortable continuing. I was PIC; wholly responsible for the safety of this flight. There is no aviation weather reporting in the [valley]. If I had known that; say; ZZZ5 was socked in; I would probably not have taken off.what went right:my training for how to respond to VFR-into-IMC kicked in; and it worked. In addition; the simulated instrument work I have done for my instrument rating (in progress) undoubtedly helped me make the 180 degree turn successfully. I did not become disoriented in IMC. Once I and my passenger realized that we were in an emergency situation; we effectively used all the available resources to plan and execute a diversion. Other observations: I used the terrain feature of the GTN750 to execute a turn in IMC amid terrain. Without that feature; I would have had to partly guess the best direction for the turn; and we might have flown into the side of a hill. On the other hand; our ability to rely on the terrain feature was part of why we chose to continue further into bad weather. Looking back; I'm amazed how fast this all was. It seemed slow at the time; but in actuality it was just over ten minutes from unproblematic VFR to almost dying in a bank of low cloud.

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Original NASA ASRS Text

Title: C-177RG Private Pilot reported unexpectedly flying in IFR weather as a VFR rated pilot in mountainous terrain resulting in an emergency situation.

Narrative: Around XA:25 on [date]; my passenger and I departed ZZZ; bound for ZZZ1. My passenger was a friend; colleague; and [XX] hour student pilot; for whom this was the first cross-country experience in a small plane. Weather at our point of departure was clear. The departure from ZZZ and crossing of [Mountain Pass] were uneventful. At our destination; a front was forecast to come in around midday; bringing rain and lowered ceilings. Nevertheless; terminal forecasts near [destination area] were VFR; and we believed we would land before the front arrived at ZZZ1. When clouds are forecast for the [destination area] area; it is often possible to safely cross the [mountain range] by flying VFR under clouds on the west side; the east side is usually free of low cloud for most months of the year. I have done this a number of times; and I expected to be able to do something similar on this flight. Around ZZZ2 we got our first look at the west side weather. The clouds were dark; tall and forbidding; rags of fog were starting to form in some hollows around some peaks. The [enroute station] ASOS suddenly dropped from reporting ceilings of around 6;000' to 700'; the temperature/dew point spread was only two degrees. At XA:50 I called a diversion; and after a brief stop at ZZZ3; we went to ZZZ4 to take on fuel and consider our options. I briefed the weather at ZZZ4; and decided that the worst weather was to the north. My passenger independently looked at the weather; and came to the same conclusion. Terminal forecasts near our destination were 3;000 to 5;000'; 6+ miles visibility. There were no terminal forecasts along our route; so we relied on the GFA [Graphical Forecasts for Aviation] tool; weather radar; and the Windy app to build a picture of the intervening weather. Based on that; we expected to go under a layer of mid-level cloud west of the crest; but to be able to make the trip VFR. We decided on a [new] route south of [mountain]. We took off from ZZZ4 about XC:45; with unlimited visibility and only some high cloud. We climbed to 8;500 by about 10 miles east of [lake]. Around [lake]; we encountered a layer of cloud at our altitude; and descended to 6;500 by [mountain pass 1]. At [mountain pass 1]; I looked northwest along our intended route and saw the shoulders of [large mountain] were shrouded in cloud. Looking west along the valley I saw a bank of clouds at and below our level; but with an apparent path underneath. I decided to reroute us via ZZZ5; under the clouds. I descended to 3;300' by three miles west of ZZZ6; about XD:20. We were under a layer of smooth cloud but well clear of the cloud with plenty of visibility. A couple of minutes later; we flew into intense rain that dropped flight visibility to (I would estimate) three miles. A couple of minutes later; the rain eased off; but we were flying through mist; below ragged clouds with visibility varying between three and five miles. My passenger and I discussed the situation; and decided that this was probably a narrow band of bad weather associated with the front; and that we could continue carefully through it and come out in good weather on the other side. I switched the GTN750 in my panel to Terrain mode; to back up our visual way finding; reduced power and put in flaps to slow the plane down. We were roughly ten miles west of ZZZ6. Over the next five or so minutes; we flew down the center of the valley; looking forward constantly to pick out the terrain and see if the weather was getting better or worse. We were also slowly descending; but I was not particularly conscious of that fact; as I was focused on looking out the windows. Around XD:30 we came over the east shore of [lake 1]; elevation 770'; we were 2 ;200'. I had to descend again to avoid low-hanging cloud. Flight visibility also started to reduce further; I would guess between one to two miles. I started to think that we should turn around; but figured we'd look around one more corner. As we turned around a bluff on the north shore of the lake; I saw a cloud in front of me; and before I could decide what action to take; flew right into it. I knew I had to execute a 180 as I had been taught in training; or we would likely die. My passenger said the same. I looked at the terrain map and chose a left turn; where there was much more room. I executed a standard rate turn to the left using instruments only; at about 2;000'. After about one and a half minutes in IMC we broke out on an eastbound heading. As we flew away from the lake; visibility improved slightly to about three miles and we climbed to 2;500'. Clouds were probably 200'-500' above us. My passenger and I discussed the situation; acknowledged that we were in an emergency; and that our overriding goal now was to land the plane such that we could walk away. We decided to try for ZZZ5; now about four miles north. I gave him my iPad; and told him to manage the GTN750 and brief me on the airport. At about XD:40 we found our path to ZZZ5 blocked by a wall of cloud; and we turned around; once again heading east up the valley from a point northeast of [lake 1]. We discussed emergency landing options; and whether we should attempt to fly back to ZZZ6; about 20 miles east. My passenger suggested ZZZ7; a charted private turf strip about five miles east of our position. I agreed that if the strip was usable for us; we would land. The strip looked to be in good condition; so I executed a straight-in landing to the east; touching down uneventfully at about XD:45. We were picked up by car from ZZZ7 about two hours later. During this time; the weather deteriorated further; with spells of heavy rain; and clouds descending further to cover the sides of the valley. In the few days since this incident; I have reflected extensively on what went wrong and what went right.What went wrong:I chose to continue into inclement and deteriorating weather amidst mountainous terrain. I think my judgment simply failed me in this case. I had diverted or rerouted two other times before that day due to weather; those calls were right; this one was wrong. I don't think I'll make this mistake again. I had a false; overly-optimistic mental picture of the weather; which fed into my choice to continue. I have had little experience flying in heavy rain; or in conditions of marginal visibility. I have flown about 180 hours of VMC; about 18 hours of simulated IMC; and two hours of actual IMC in clouds (with an instructor). I was blindsided by how rain can reduce visibility from unlimited to marginal in an instant. I didn't quite know what heavy rain looks like; now I do. I was distracted by the marginal weather and did not fully process the fact that we were slowly descending for several minutes between ZZZ6 and Lake. We were being wedged in by clouds and terrain and it took a while to realize how wedged in we were. I should have disregarded the fact that my passenger; an even less experienced pilot than me; was comfortable continuing. I was PIC; wholly responsible for the safety of this flight. There is no aviation weather reporting in the [Valley]. If I had known that; say; ZZZ5 was socked in; I would probably not have taken off.What went right:My training for how to respond to VFR-into-IMC kicked in; and it worked. In addition; the simulated instrument work I have done for my instrument rating (in progress) undoubtedly helped me make the 180 degree turn successfully. I did not become disoriented in IMC. Once I and my passenger realized that we were in an emergency situation; we effectively used all the available resources to plan and execute a diversion. Other observations: I used the Terrain feature of the GTN750 to execute a turn in IMC amid terrain. Without that feature; I would have had to partly guess the best direction for the turn; and we might have flown into the side of a hill. On the other hand; our ability to rely on the Terrain feature was part of why we chose to continue further into bad weather. Looking back; I'm amazed how fast this all was. It seemed slow at the time; but in actuality it was just over ten minutes from unproblematic VFR to almost dying in a bank of low cloud.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.