Basically, wind chill is a way to measure how fast heat is pulled from something, down to the ambient temp...
Yes, you can stretch synthetic oil changes, but I wouldn't get carried away with that...
SR
Good quality Synth will perform a little better, esp. in terms of cold flow. But, as many gens being discussed in this thread hold less oil than my largest coffee mug, I just change out no later than rated hours - easy enough to do, and not expensive.
One advantage to continuous runs (extended outage) is the engine is plenty hot... no fear of condensation in oil.....
Any spec rated oil will work; this is one I like for older equipment spec'd for straight 30:
AMSOIL Formula 4-Stroke Synthetic Small Engine Oil
Rgds, D.