It's going to be no surprise to most of you to hear that it's been a dry winter so far. You don't need to look any farther than the fact that much of the Central Coast has been dealing with fires at a time of year when we're more likely to be worrying about erosion. Even when we did get a little rain the week before Christmas, it served mostly to highlight just how unusually bare the ground was for late December:
While the dry weather has meant pleasant afternoons that felt more like October than December, it was also very cold at night. How cold? In December, we saw 20 nights of frost at the vineyard. Now a winter frost isn't unusual. We typically get 30-40 nights a year that drop below freezing, and December is typically our coldest month. Nor is it detrimental. Grapevines benefit from being forced into dormancy, as it keeps them from expending energy they'll need in the spring on winter growth that won't help ripen grapes.
But it is unusual to see so many frost nights in a single month, and even more unusual for so many of those days to be warm. The average high temperature in December was 68.9 degrees, and sixteen days made it into the 70s. One day (December 13th) managed to set both Paso Robles' record high (73) and low (22) for that date. What was the culprit? Record low humidities, and a near-total lack of cloud cover. Eighteen days saw relative humidity levels drop into the teens, with a stretch in early December where four days in a week saw levels in the single digits. How unusual is that? December 2016, which wasn't even all that wet, didn't see a single relative humidity reading as low as 30%. Neither December 2015 nor December 2014 saw any days below 20%. You have to go back to 2013, which for most of California's was its driest year on record, to find anything comparable, and even they only saw 11 days of relative humidity below 20%. No wonder our December brought us only a paltry 0.07" of rain.
The impact on the vineyard is likely to depend on what we see in coming weeks and months. Typically at this point we'd expect to have accumulated 8.15" of rain. This year, we've only gotten 1.42", or 17% of normal. Our cover crop has barely sprouted, and the soil is dry down through most of the root zone. But there's still time. Typically, more than two-thirds of our annual rainfall comes after the new year, and our two wettest months are, on average, January and February. That said, there's no question that we're behind. Even with normal rainfall the rest of the winter, we'd only be at 73% of normal precipitation:
There's no guarantee that we'll see normal rainfall the rest of the winter, either. The Pacific has settled into a mild La Nina pattern, which typically produces drier than normal winters in California. That said, for the first time in over a month the near-term forecast is calling for some wet weather. The ridge of high pressure that has been responsible for our dry December is breaking down, and two small storm systems are forecast to impact the Central Coast this week. Even better, the following week is likely to see the storm track shift south enough for some potentially more significant rainfall. Meteorologist John Lindsey shared the following graphic on social media, showing the two major model predictions of ten-day precipitation:
While neither projection suggests we'll get drenched, both show an inch or two of rain as we enter January. That's not enough to get down deep into the zone where our dry-farmed vines' roots mostly are, but every bit helps. At the least, it should get the cover crop germinated, and ensure that our flock of sheep, alpacas, donkeys, and llama has enough to eat this winter without our having to supplement.
Given how dry it's been so far this winter, we'll take whatever we can get. Fingers crossed, everyone, please.