A good climate is essential for wine quality. This is why some vintages are better than others.
The sun ripens the grapes and turns the acidity into sugar, which will be transformed into alcohol during fermentation. However, too much sun can affect the quality of the harvest, producing unbalanced, too alcoholic wines with not enough acidity. The rain lowers the tannins of grapes skin. If too rainy, the risk is a wine without character.
There is a multitude of microclimates in France due to the altitude, the proximity to rivers, woods, mountains, etc. Therefore, winemakers have to adapt their work to weather conditions. For example, a grape can be ready to be harvested the 10th of August at Montpellier, the 10th of September in Burgundy but only the 20th of the same month in Alsace.