C172 pilot reported landing on a highway after the weather degraded rapidly.

Narrative:

The weather was VFR with light rain and ceilings of approximately 8;000 ft. Prior to my departure I used fore flight and aviationweather.gov to check the weather for this flight and found both sources to represent VFR conditions for the duration of this flight. [During the flight] I found dense mountain obscuration and ceilings zero ft above the ground. I turned around immediately and found the ceilings I had just flown under to have diminished greatly to a very low level above the ground. At this time I also encountered a significant downward orographic force causing me to quickly lose approximately 800 ft of elevation. With the weather degrading rapidly; for the safety of this flight; I found myself with no other option than to land on [a] highway. I did so safely and without incident to myself; the aircraft; [or] other life or property. After approximately 30 minutes the weather had improved to VFR once again. I decided to leave the highway for [a nearby airport] were I stayed. During both the landing on [the] highway and departure I did not impede traffic. Everything I did during this incident was done in accordance with far part 91-3 for the safety of the flight. If I had not acted in this manner I would not have survived the rapidly changing weather. I have learned a great deal from this incident. This event has taught me how quickly weather conditions can deteriorate. As a commercial pilot I will continue further training and seek resources to mitigate the factors of weather.

Original NASA ASRS Text

Title: C172 pilot reported landing on a highway after the weather degraded rapidly.

Narrative: The weather was VFR with light rain and ceilings of approximately 8;000 ft. Prior to my departure I used Fore Flight and Aviationweather.gov to check the weather for this flight and found both sources to represent VFR conditions for the duration of this flight. [During the flight] I found dense mountain obscuration and ceilings zero ft above the ground. I turned around immediately and found the ceilings I had just flown under to have diminished greatly to a very low level above the ground. At this time I also encountered a significant downward orographic force causing me to quickly lose approximately 800 ft of elevation. With the weather degrading rapidly; for the safety of this flight; I found myself with no other option than to land on [a] highway. I did so safely and without incident to myself; the aircraft; [or] other life or property. After approximately 30 minutes the weather had improved to VFR once again. I decided to leave the highway for [a nearby airport] were I stayed. During both the landing on [the] highway and departure I did not impede traffic. Everything I did during this incident was done in accordance with FAR Part 91-3 for the safety of the flight. If I had not acted in this manner I would not have survived the rapidly changing weather. I have learned a great deal from this incident. This event has taught me how quickly weather conditions can deteriorate. As a Commercial Pilot I will continue further training and seek resources to mitigate the factors of weather.

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.

Attributes
ACN	1519104
Time
Date	201802
Local Time Of Day	0601-1200
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	None
Person 1
Function	Single Pilot Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Commercial Flight Crew Instrument
Events
Anomaly	Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types Inflight Event / Encounter Weather / Turbulence Inflight Event / Encounter VFR In IMC