The area benefits from the largest swing between high daytime and low nighttime temperatures of any region in California as a result of the cool marine air that flows east through the Templeton Gap and south along the Salinas River Valley from the Monterey Bay. The region’s summer is characterized by warm, clear days, generally unencumbered by clouds, fog or severe winds. Daytime high temperatures in the summer typically fall between 85 and 105 degrees Fahrenheit, but nighttime low temperatures usually can drop by 40 to 50 degrees, cooled by a marine layer that moves over the region in the mid to late afternoon. This fluctuation is considered a key by winemakers and wine grape growers to attain the intense varietal character displayed in wine grapes from the area.
September, October and the first half of November are typically rain-free and warm, giving Paso Robles vines the advantage of time to produce fully mature fruit, while the overnight cooling keeps the grapes’ acid chemistry in balance. The first rainfall of the season is typically about two weeks later than Napa or Sonoma, and a month later than Mendocino, giving winemakers the luxury of waiting for optimal ripeness. Winter temperatures tend to dip into the low twenties in the cooler regions, with most vineyards becoming fully dormant by mid-December. Frost is also a potential threat through mid-May, especially following a northern weather system.
Rainfall
The rainfall of the region, like its climate and soils, varies greatly depending on the vineyard’s proximity to the Pacific Ocean and the Templeton Gap. Average rainfall for the city of Paso Robles is 15.5 inches, but rainfall ranges from eight inches in the eastern portions of the AVA to as much as 45 inches on the far western ridges. The first rains typically arrive in early to mid November, with the heaviest amounts usually occurring in January through March. These rain totals are typically dominated by relatively few, but substantial, Pacific storms that can contribute several inches of rain in just a few days.
Elevation
The City of Paso Robles rests at 740 feet above sea level. Paso Robles vineyards east of the Salinas River range from 700 to 1,000 feet in elevation while those to the west range from 850 to 2,000 feet.
Growing Season
Due to cool nights and warm days, and typically late rains, Paso Robles vines tend to have a longer growing season and grapes have more hang time compared to other wine regions, resulting in fully mature fruit whose acid chemistry is kept in balance through the area’s overnight cooling.
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