“A great wine education class. I was amazed by the instructor's wealth of knowledge, the
great wines to taste and talk about, and the small, intimate class size. A fun way to learn a lot
—Will, Ritchie Creek Vineyards
CA does have climatic variation from year to year. These variations may be too subtle for immigrants from Chicago and Minnesota to recognize, but vinifera grape vines are more sensitive (read ‘delicate’) than third-generation Poles raised in Chicago or Scandinavians born in Minneapolis.
California’s flip-side to winter kill in the Midwest is an occasional winter so mild there are no freezes at all. That circumstance allows grape pests to overwinter in sufficient numbers to cause significant crop damage during the subsequent spring and summer. More commonly, severe rain storms during a winter season can cause flooding in sections of vineyard, even submerging the vines for some number of hours. Despite hysterical media coverage, these events are of little consequence to CA vineyards. Flood waters recede quickly, and permanent damage only occurs if vines or trellises are ripped out of the ground by the force of the flood current. A more likely, and much more dramatic consequence of heavy rain is earth subsidence (i.e. mudslides) where small numbers of vines are eradicated on terraced, hillside vineyards. Long-term, gradual erosion is a much more sinister issue.
The amount of rainfall during January and February (when CA gets 60 percent of its precipitation) is not as important as the amount during March and April when vines are beginning to grow. Drought during winter, as happened in 1976 and 1977, then again in 1987 and 1988, can have serious repercussions. It reduces the amount of water available for spring irrigation and frost protection, as well as the amount of water retained in the ground. Normal rainfall ranges annually from 20 inches to 40 inches for North Coast districts; 15 inches to 25 inches for the Central Coast; and 35 inches to 60 inches in the Sierra Foothills (depending on elevation). Those figures are, however, averages based on periods of more than 100 years. In actuality, the common experience is several years at 10 inches followed by several years at 40 inches (as depicted in the chart of annual peak flows for an undammed Mendocino River). None of the recent fluctuations between drought and flood are out of the ordinary. Analysis of tree growth rings clearly documents periods in the last millennium when severe drought lasted 15-20 years in CA, and periods when rainfall was triple the wettest years of the 20th century. In severe drought conditions vine metabolism is restricted. High alcohol, low flavor is the norm in those circumstances. The first year of a drought often produces some concentrated, impressive, long-lived wines, but subsequent years more often produce awkward, rough, charmless wines.
Frost danger usually passes in CA by mid April. Although in 1980 there was a frost in Napa Valley on May 10th, and in 1970 there were 20 nights of frost in Apr there. Frost is a matter of considerable concern in CA because so many vineyards are planted on valley floors. Overhead sprinklers are usually the first line of defense. They are expensive though, because most of the water needed to run them must be stored in some sort of impoundment reservoir. Wind machines are also seen commonly where topography is suitable. Diesel smudge pots are no longer used. Long pruning is an old-time method whereby foot-long spurs are left on the vines into Spring, and then pruned off just when the plants begin to push buds. That operation shocks the vines into remaining dormant another couple of weeks. The technique is rare, but some small vineyardists swear by it.
Rain during flowering (average occurrence around the first week of June) is extremely rare in CA, although 1995 saw some in the southern districts and 1994 even included a freak hail storm the last week of May in Napa. More germane is the possibility of poor pollination due to sluggish performance by bees in overcast, cool or foggy weather. Equally deleterious can be berry shatter from spikes of really hot weather during flowering.
Overall temperatures during the July and August ripening period in CA definitely play a role in determining wine quality. By the end of Aug/early September, wineries are usually starting to harvest grapes in CA's North Coast. The Central Valley usually starts three weeks earlier; the Central Coast three weeks later. Weather during the September harvest period is a crucial quality indice in CA because of the generally warm temperatures. Rain during harvest is commonplace in most northern European wine growing districts, but cold temperatures by that time there slow the growth of rots, molds, and mildews, and rapidly shortening days have already stopped vine growth and lignified stems. Significant rain during September in CA can destroy the quality of the crop with rot in the space of a week. Winemakers who produce very limited quantities can hand-sort clusters on a triage board before they go into the crusher. Large wineries must usually forego this pleasure. Either way, vines will have absorbed a lot of water which dilutes flavors, acid and sugar in the berries. Brief showers do not cause problems. Actually the most typical weather pattern for CA's North Coast winegrowing districts is a couple days of overcast and drizzle in late September (not enough to affect the grapes), followed by two to three weeks of sunny weather called Indian Summer. Spectators at Stanford football games in early October go shirtless to improve their tans; while their friends at Notre Dame wear suits, parkas and ear cozies.
One weather pattern is unusual because of its effect on September rains in CA. El Niño causes a warming of the surface waters in the Pacific Ocean driving everything further north than usual. Warm water fish like marlin come into Monterey Bay, bonita are caught off the Sonoma coast. September is hurricane season in the northern hemisphere. In the eastern Pacific these storms normally don't get any further north than Mexico, although they always cause big surf in Baja. In El Niño conditions (1982 and '83 are the classic example) rain not only arrives in CA in September, it arrives from the south (rather than the northwest), and it is tropically warm (not Alaska cold). El Niño conditions are abnormal, but they do seem to return on a 10-15 year cycle.
The other side of the weather issue occurs when CA's harvest is attended by heat waves. In extremely hot weather, grapes ripen so quickly that large wineries can not pick them nor process them through their equipment fast enough. Inevitably some grapes will be left on the vine until they are over-ripe. Small wineries are less likely to have this problem because the volume of grapes they process allows more flexibility. In fact many extremely expensive wines from the 1997 vintage on in places like Napa Valley have been made from grapes intentionally left on the vine an extra couple of weeks. It can be a delicate maneuver ~ there is a thin line between über ripe concentrated flavor and raisins.