The climate of planet Earth is beset by natural phenomena and variations in topography that affect the weather and temperature of any given region.  Three general climate levels define our planet: macroclimate (regional), mesoclimate (local or site specific), and microclimate (ground to vines).

The macroclimate covers hundreds or thousands of miles, and can be easily determined in most cases. Factors that determine a region’s climate include topography and world weather patterns.  Proximity to large bodies of water can have a beneficial effect on vineyards, as cool air flows can regulate temperatures that soar further inland in summer, and drop harshly in winter.

Mesoclimate effects are mostly related to vineyard orientation, elevation and slope. Depending on the locale, valleys can be warmer or cooler then the surrounding mountains or hills. It’s important to know the specific weather patterns for your local area to determine site placement and grape variety to grow.

Microclimate refers to the conditions from soil to vine canopy.  This is the climate level that can be most easily influenced by the vineyard manager, via training systems and proper vine management.

Grapes generally prefer a long, cool growing season, with a lack of extreme temperatures from spring to fall. Steady temperatures can have a positive effect on grape maturity and ripening. However, some varieties can withstand much more variation in temperature than others. Extremely high temperatures yield grapes that produce flabby-tasting wine, while not enough heat throughout the season can cause grapes not to ripen.

Vine growth does not typically occur at temperatures below 50ºF. Any vineyard needs a certain amount of heat units to produce fruit. Heat units are typically measured in Degree Days, which are calculated by subtracting 50ºF from the average daily temperature. The sum of the degree days is accumulated throughout the growing season.  This figure is used to determine site suitability, and compare the area to other grape-growing regions.  Depending on the region of the world, grapes can be grown at sites producing 1600 degree days or fewer, or as many as 4000.

Grapevines also need water to produce their crop.  A lower-limit of 24 inches of rainfall per year is a good guide as to whether an area can support winegrapes.  Any less than this, and the site will probably need to be irrigated, or supplemented with water in some way. Too much rain or humidity can ruin grapevines and the fruit which they produce.

Extremely cold temperatures can damage or kill grapevines, even in winter when they are dormant. If temperatures dip below 0ºF in an area, anyone planting vines there will want to make sure that they select a hardy rootstock that can withstand the freezing temperatures. 

Once the buds reveal themselves in the spring, frost is the grapevine’s worst enemy. Temperatures even a few degrees below freezing can totally wipe out an entire vineyard for that growing season.  Avoid planting in low-lying areas, where frost and fog tend to pocket.  It’s also a good idea to avoid grape varieties with early bud breakout if spring frosts are a problem in your area.

With the recent focus on global-warming, some think that worldwide climate changes may be coming that could affect popular wine regions, such as Napa Valley , California .  With the potential increase in degree days, what has been a perfect area for growing grapes could gradually shift northward toward the pole, making Oregon the place to grow Chardonnay and Cabernet Sauvignon.