|Ascona Vineyard, Santa Cruz Mountains|
Let's start by getting some boring science stuff out of the way.
Last winter saw one of the strongest La Niña events ever recorded. When this occurs the surface temperature of equatorial waters cools by several degrees, which in turn alters the path of the jet stream that crosses the USA. The effect usually fades in spring, but in 2011 it remained strong much later than usual. The jet stream remained farther south and blew more strongly. The effects were felt across the country, with many states experiencing near record highs or lows of temperature and rainfall.
In California the effect resulted in a spring that was colder, wetter and later than usual. The cold weather delayed budbreak, while rains during bloom affected 'set' - the formation of the grape cluster as flowers turn into berries. Yields were affected across the state, with many regions reporting 20% to 30% below normal, but the Santa Cruz Mountains vineyards were impacted more severely, particularly at higher elevations. Growers are typically reporting yields 40% to 60% below normal, with some vineyards being written off entirely.
Summer was long and cool without unexpected heat spikes; this increased risk of mildew - growers had to be diligent about spraying. Mary Lindsay of Muns Vineyard reported adding potassium to sprays to help boost vine health and encourage better and more even ripening throughout the vineyard. The cool weather did little to help the already late running harvest, and some light October rains brought an additional threat of botrytis. Paul Romero of Stefania Wine called it "a tough, unhappy year - 2010's work with 2008's yields ... larger berries than 2008 but close in quality [and] without the tannin issues".
The expectation is for some elegant, balanced wines at lower alcohol levels. Bradley Brown of Big Basin vineyards said "Quality appears to be remarkable and for those who picked at the right time and maintained healthy vineyards, this could be one of the best vintages in a long time."