But Diurnal Temperature Change Isn't Everything

Have you ever been to the Black Hills of South Dakota? We're talking the border with Wyoming to the northwest of Rapid City. Specifically, let's visit the town of Spearfish. It's a small town, by virtually any standards. Once a local home for the Sioux, when gold was discovered in 1876, the local Gold Rush was on and the Sioux gradually had their land taken over. 

While we sometimes talk about history, this is not a history blog. And, when we go to our local wine shop, well, I don't know about you, but I have never asked my local wine merchant if they have any great South Dakota wine. In fact, I've never seen a review of a South Dakota wine, heard of any of the northern US winemakers talk about their penchant for South Dakota grapes, or even make an association with South Dakota.

But, I googled it and there are some South Dakota wineries. And, based on the names of the wines, I would categorize their clientele as bikers. For example, when your best seller is called Phat Hogg, you're not dealing with the wine cognoscenti.

So, why Spearfish? Sitting in the Black Hills just to the east of the Rockies, Spearfish is also known for its sometimes extreme climate. When we talk about diurnal temperature shifts of 50 degrees as being extreme, Spearfish can have them ... well ... a lot faster than that.

You see, Spearfish, due to its location where the winds coming off the Rockies can slide through gaps, is particularly susceptible to foehns, or as they are known locally, and generally in the northern plains of the US and Canada, Chinook winds. What these winds can do is just nuts.

The record high temperature in Spearfish is 110F/43.4C. That's similar to some of the warmer places in Napa. And, in Napa, particularly in places, both at elevation and with exposure to San Pablo Bay, we remarked about places with record highs in that vicinity and pretty extreme diurnal temperature shifts. Nothing in Napa can hold a candle to Spearfish.

It's not an everyday occurrence, but back on a cold, or was it warm, day in January 1943, the temperature at 7:30AM local time was -4F/-20C. And the Chinook winds came. And they blew rapidly. And, the snow melted. Quickly. At 7:32AM, the temperature was 45F (I know this stuff because I revel in trivia). By 9AM, the temperature was 54F/12C and then the Chinook winds did their thing again and by 9:27, it was back to -4F/-20C.

Based on everything we've learned recently, this should be perfect for producing great wines. It's not. There's no predictability. It rains too much in the summer and is too dry in the winter. Most of the summer is too cool to grow hot weather grapes, but at least a few times each summer, it gets way too hot for cool weather grapes. Even on that day back in 1943, any positive effects of the temperature shift are not pronounced enough for long enough to help. 

So, while we usually talk about great things about wine. Today, we don't. Today is just to tell you that whatever rules you have picked up from reading the daily wine thought on my mind, the first rule of winemaking is there is no first rule.