The Southern Hemisphere’s predominant airflow, the “roaring forties”, passes over the South Island in a westerly fashion. When it hits the Southern Alps, most of its moisture precipitates on the Western side, forming an important rain shadow to the east. Up to five metres (5000mm) of rain can fall each year on the Western Ranges, whereas at Rippon, only fifty kilometres away, our annual rainfall is around 600mm. Most of this falls in the springtime. The summers are hot and dry with a heat summation range of 700-1250HDD. An extended late-summer to autumn season, with a large a large diurnal temperature range (up to 25°C), allows the fruit to ripen slowly with tight, locked-in flavours. Winters are cold, but not extreme. Whilst the winter snow level sits about one third of the way down our surrounding mountains (roughly 500 metres above us), it only falls on the vineyard once or twice a year and melts quickly the next day.
Whilst Rippon is part of Central Otago, it has several important local meteorological attributes which are unique to its site.
Proximity to the Main Divide
From Rippon we can see clearly the heavily glaciated ridgeline between Mount Avalanche and Rob Roy Peak. On the other side of this divide, water flows down the valleys to the west and out to the Tasman Sea. On our side, water makes its way down the Matukituki River, into the Lake and inevitably down the Clutha River to the Pacific Ocean. During the many weak westerly fronts which buffet the West Coast during the summer, heavy cloud systems will bank up on this ridgeline. Depending on the strength of the system, wet clouds will eventually break away from this bank and make their way east, all the time slowly breaking apart and drying up. The Wanaka basin is the first to receive these clouds and more often than not they do not make it much further. This means that although Central Otago is the hottest, coldest and driest region in New Zealand, Wanaka is slightly more temperate than further down the valley towards Lowburn, Bannockburn and Alexandra.
Proximity to the Lake
The risk of frost in Central Otago is a very real one at both ends of the growing season. This is truly a marginal grape-growing area. The core temperature of Lake Wanaka only changes two or three degrees from summer to winter. The presence of this large body of water next to the vines acts like a big hot water bottle on such cold mornings where frost is a risk. We estimate that it may equate to as much as a four-degree difference from hilltop to lakefront.
Perpetual airflow is created by a water cascade, which falls down Mount Roy (the 1800 metre mountain that the vineyard backs onto). Air is drawn down the mountain, across the north facing slope of the vineyard and out on to the lake. This is also thought to be beneficial on mornings of frost risk. No protection, natural or mechanical, will ever be fool proof. Understanding and managing this risk has always been an essential part of living here.
A small, but important island of hard rock, sits out in front of the site where the vines are planted. This “Roche-Moutonee” has been left by the ancient glacier and is not only the centrepiece of Rippon’s view, but also a buffer against the harsh, prevailing Nor-West winds. These powerful winds, having dumped all their moisture on the West Coast, can be extremely dry and are able to cause heavy stress to both the vine and vigneron alike. Even in periods of severe wind where the lake may be white with froth, the bay in front of the vineyard is relatively calm. Ruby Island, although it doesn’t stop the wind, spoils it, throwing it up, causing it to roll over the property rather than hitting it full-force.