C172 student pilot; completing a long cross-country flight; encountered unforcasted fog upon return ...

Narrative:

I was completing my long X/C and the taf's reported VFR conditions long after my proposed time of return to [departure airport]. I checked the weather forecast for the route of my flight and it also reported no fog at the proposed time of my enroute legs. I encountered fog outside of the class D airspace below my aircraft by at least 1;500 feet upon my return to [departure airport]. I saw I could remain easily in VFR conditions; but still fly within the airspace. I requested a special VFR clearance so I could attempt a straight-in approach to runway 34; since fog was moving in quickly. Upon my descent; I lost visual contact with the runway approximately 3 miles south of the approach end. I was above the fog in VFR condition and made the decision to break off my descent to the east and land at [another airport]. At no time was I in IMC; or not maintain visual contact with the ground. The fog bank moved in sooner than predicted and was only over the airport runway. The east and northeast of the airport had greater than 6 miles visibility; no fog and light haze. I could see [a landmark] and I knew I was able to land at [the other airport].... I maintained visibility and cloud clearance according to the limitations placed on my solo endorsement.

Original NASA ASRS Text

Title: C172 Student Pilot; completing a long cross-country flight; encountered unforcasted fog upon return to departure airport and landed VFR at a nearby airport.

Narrative: I was completing my long X/C and the TAF's reported VFR conditions long after my proposed time of return to [departure airport]. I checked the weather forecast for the route of my flight and it also reported no fog at the proposed time of my enroute legs. I encountered fog outside of the Class D Airspace below my aircraft by at least 1;500 feet upon my return to [departure airport]. I saw I could remain easily in VFR conditions; but still fly within the airspace. I requested a Special VFR Clearance so I could attempt a straight-in approach to Runway 34; since fog was moving in quickly. Upon my descent; I lost visual contact with the runway approximately 3 miles south of the approach end. I was above the fog in VFR condition and made the decision to break off my descent to the east and land at [another airport]. At no time was I in IMC; or not maintain visual contact with the ground. The fog bank moved in sooner than predicted and was only over the airport runway. The east and northeast of the airport had greater than 6 miles visibility; no fog and light haze. I could see [a landmark] and I knew I was able to land at [the other airport].... I maintained visibility and cloud clearance according to the limitations placed on my solo endorsement.

Data retrieved from NASA's ASRS site as of July 2013 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	1124350
Time
Date	201310
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Tower
State Reference	US
Environment
Light	Dusk
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	Visual Approach
Flight Plan	VFR
Person 1
Function	Single Pilot
Qualification	Flight Crew Student
Events
Anomaly	Inflight Event / Encounter Weather / Turbulence

C172 student pilot; completing a long cross-country flight; encountered unforcasted fog upon return to departure airport and landed VFR at a nearby airport.