Topography and Climate
Adapted from the Ribbon Ridge AVA petition.
Ribbon Ridge extends southward from the Chehalem Mountains and rises above the floor of the Chehalem Valley from approximately 200 feet to an elevation of 683 feet. Ribbon Ridge Road runs north to south along its spine. The ridge is defined on the east and west by the watersheds that fall away from the road in both directions. It is separated from the Chehalem Mountains by Ayres Creek on the north and a creek known locally as Dopp Creek, which runs parallel to Dopp Road, on the east. Though these two creeks begin less than 1000 feet apart, Dopp Creek flows south to form the eastern boundary of Ribbon Ridge and eventually empties into Chehalem Creek, which flows into the Willamette River to the south. Ayres Creek flows west-northwest to help form Wapato Lake, which drains into the Tualatin River to the north and subsequently into the Willamette River. On the western side of Ribbon Ridge, the Chehalem Creek Valley dramatically separates Ribbon Ridge from the sub-Coast Range hillsides that are collectively proposed as the Yamhill-Carlton District AVA. There is a gorge-like drop of three hundred feet or more into the narrow quarter-mile ravine that widens at the foot of Ribbon Ridge into the broad, flat Chehalem Valley dividing the Chehalem Mountains from the Red Hills. This cut more than any other feature shows the separate nature of Ribbon Ridge's formation as an uplifted landmass of unique origin.
From the air, Ribbon Ridge appears as an island, broken off from the higher landmasses that surround it and floating free above the Chehalem Valley floor. The island-like characteristics and surrounding land masses tend to shield and uniquely protect Ribbon Ridge from many of the extremes that affect other agricultural microclimates in the northern Willamette Valley. There is air and water drainage on all sides. Low clouds tend to accumulate on the surrounding hilltops; fog tends to settle on the valley floor in early and late parts of the growing season. The Coast Range and Yamhill mountains to the west encourage weather systems to drop moisture before reaching Ribbon Ridge and to moderate wind extremes from Pacific storms. The Chehalem Mountains, Bald Peak and Portland hill systems to the north tend to protect this area from Columbia Gorge and eastern Oregon weather systems that deliver extreme cold in winter and heat or winds in the summer. The Dundee Hills to the south shield Ribbon Ridge from extreme winds that funnel through the Van Duzer corridor, both hot in the summer and cold in the winter.
Analysis of compiled daily weather data comparing exposed valley floor weather stations such as Salem, McMinnville, and Portland airports to hillside vineyard stations for the four years 1998-2001 shows a tendency towards slightly warmer and drier conditions on grape growing hillsides of the northern valley, such as Ribbon Ridge.
The differences are even more significant during the grape-growing season (April-October), with the nature of hillside warming being especially important for grape growing. Specifically, hillside data showed higher minimum daily temperatures during early and late growing season (2-3Â°F) than those of exposed valley floor sites. As well, higher maximum daily temperatures are seen on average because of early and late season increases (2-7 Degrees F) and despite depressed daily mid-summer (June-August) temperatures (2-7 Degrees F). This moderation permits early growth in the spring, consistent and even ripening with retention of acids over the summer, and a long, full ripening in the fall, at the end of the growing season.
Degree-day accumulations (50 Degrees F base) are less on the hillside sites by as much as 10 Percent (2455), but earlier starts to warming, less nighttime temperature drop, and clipped heat spikes in mid-summer provide a consistency and protection of cool climate elegance, with nonetheless adequate ripening.
Precipitation on protected hillsides in the subject areas is 7-10 inches less than precipitation at unprotected valley sites. This represents a reduction in precipitation of 20-26 Percent.