Cristom winery is adjacent to Tunkalilla Vineyard and has collected weather statistics since 1986, which give a reliable picture of the climate of this special part of the Eola Hills.
The heat summation accumulated during the 7 month growing season from April to October, calculated from the average temperature of each month that exceeds 50ºF (10ºC), is a 2493ºF days (1385ºC days) compared to Burgundy (Dijon) at 2075ºF days (1153ºC days).
The daily temperature range over the growing season is a very moderate 18.7ºF (10.4º C) and compares to Burgundy at 18.2ºF (10.1ºC).
The climate at Tunkalilla Vineyard is defined in a macro sense by its location at 45ºN in the Willamette Valley Oregon, on the western side of the Cascades and in a meso sense by its south-facing slope at 600 feet ASL, adjacent to the afternoon cooling influence of the Van Duzer Corridor.
In a micro sense at plant level, the sloping rocky red Jory soil absorbs heat during the day, reducing day temperature and releasing the heat at night with the overall effect of reducing the amplitude of the day/night temperature range. The plant is able to work the full 24 hours of the day through the entire summer. Very importantly the soil absorption of heat is conducted efficiently by its high rock content to the deep roots of the vine keeping them growing and producing the fruit ripening hormones so essential to quality.
The humidity in the afternoon is moderately high (>50%) as the cool moist air of the Pacific meets the warm air of the Valley and this reduces transpiration and stress on the vine, combining with the moderate daily temperature range to allow the vines to ripen grapes fully at moderate sugar levels and high natural acids.
The rainfall in the Eola Hills is dominantly in the winter (2/3rds) and totals 42 inches (1100mm's), a quantum and pattern that allows vines to be grown without or with minimal irrigation, relying on a winter subsoil saturation, gradual drying out of the upper soil layers in the spring and then relying on the deep clay bound moisture to alleviate the moderate stress of summer.
Summer rain drains rapidly off the slope and through the very friable soils diminishing the growth enhancing and detriment to quality of surplus soil water during ripening. This is a near perfect viticultural soil system.