Temperature variations in the Walla Walla valley American Viticultural Area

Variations in average growing season and ripening season temperatures within the Walla Walla Valley American Viticultural Area are related to elevation and regional and local topography. Downstream narrowing of the Walla Walla Valley creates a nocturnal cold air pool that is more pronounced during the August to October ripening season. Average growing season temperatures are generally higher and growing degree-days greater at lower elevations. Average temperatures increase with elevation to 450 m during the ripening season as temperature inversions become more pronounced and persistent. Cool air descending from the Blue Mountains lowers average growing and ripening season temperatures at sites near major streams. Adiabatic warming of down-sloping prevailing winds increases average growing season and ripening season temperatures near the base of Vansycle Ridge. Grapevines planted below 300 m have a much greater risk of damage from frosts and freezes. Variations in vineyard ground surface materials have no apparent effect on ambient air temperatures as measured by radiation shielded data loggers at a height of 1.5 m