"I always heard they [elevations] lessen diurnal range, because cold air is heavier than warm air, which means it sinks down into the valleys at night leaving the mountaintops warmer. In California, mountains like Howell, Atlas Peak, Spring etc. have a smaller day-to-night temperature spread, while the valleys — Redwood is one of the more famous — can have 50 degree spreads in a 24 hour period. Also "which can help in ripening" — I never heard that diurnal spread helps ripen grapes. Heat ripens grapes. Low nighttime temps help maintain acidity, but that's different from ripeness."

The second part about diurnal temp. differences helping to maintain acidity is certainly true, and what I meant to state in the blog post (but screwed it up!) was that the ripening is more even due to the temp. difference (i.e., better balance between acidity and ripe fruit flavors).

I did a bit more research on the first point (whether or not higher elevations accentuate or lessen diurnal temp. differences), and found conflicting evidence:

"One of the most important and beneficial factors in high elevation grapegrowing is a wide swing in diurnal temperature differences distinguished by lower night-time (cooling) temperatures. Grapes grown at higher altitudes can develop a more
favorable phenolic profile with higher levels of tannins and anthocyanins, and a more rounded tannin struc-ture due to lower levels of mortomene tannins."
(from tricycle wine co – http://www.tricyclewineco.com/tricycle/servlet/streamfil... target=”_blank”>http://74.125.93.132/search?q=cache:Evk4u2a2jgEJ:…” target=”_blank”>http://www.tricyclewineco.com/tricycle/servlet/streamfil... )

And then:
"Locations that typically have smaller diurnal temperature swings are high-elevation locations (mountain tops and hillsides more so than high plateaus) and locations with coastal influence. Coastal fog, generally thought to be a cooling influence, also serves to stabilize temperatures within the low to mid 50s (on the California West Coast)."
(from http://www.winebusiness.com/wbm/?go=getArticle&am… ).

Fodder for a future post, perhaps…?

Some other sources