Anticipating a Long-Awaited Change to Wetter Weather
Mapping out the future of Tablas Creek

A Closer Look at Paso Robles' Microclimates

This morning, I had the pleasure of sitting on a panel with Adelaida Cellars' Terry Culton, Eberle Winery's Ben Mayo, and Victor Hugo Winery's Vic Roberts for an audience of fifteen or so visiting Canadian journalists and members of the Wine Institute.  Our topic was the ageability of Paso Robles wines, and each of us showed a current and an older release of one of our wines.  I'm not sure we met exactly the goal we were set, but I think that an even more interesting discussion unfolded during the seminar.

On the panel, I showed two vintages of Esprit de Beaucastel Blanc, our Roussanne-based white Rhone blend.  It was followed by two Adelaida Syrahs, two Eberle Cabernet Sauvignons and two Victor Hugo Petite Sirahs.  So far, no big surprises.  All of these varieties are relatively heat-loving, though each benefits in its own way from the good acids and longer hangtimes provided by Paso Robles' cool nights.  But the discussion took an interesting turn when Terry admitted that it was the opportunity to work with the historic HMR Pinot Noir vineyard that brought him to Paso Robles from his position at Pinot Noir mecca Calera.  The journalists, many of whom had never before visited Paso Robles, and who had arrived just the night before so hadn't yet had the chance to explore the AVA, were genuinely amazed that it was possible to grow cool-loving Pinot Noir in proximity to these later-ripening varieties that, in France, need to be grown hundreds of miles to the south.

While the attendees had received a Paso Robles AVA map, we were asked to show on the map how the AVA broke down for climate, soils, and rainfall.  We did the best we could from the front of the room, pointing to the areas that were warmer and cooler, drier and wetter, and more and less calcareous.  But it made me wish for some better tools to show the often remarkable variations within the AVA.  So, I went back to the office today and made some.  They're not perfect, but they're better than anything I could find publicly available, and I thought I'd publish them so they could help others trying to explain the region's microclimates.  All are based on the excellent Paso Robles AVA map developed by the Paso Robles Wine Country Alliance.

First, the map with overlays of areas that are warmer and cooler.  We're an unusual coastal valley because our valley does not cut through the nearby coastal range, instead following the Salinas River north-south inside the coast range a hundred miles north to the Monterey Bay.  This means that the direct ocean influence is limited to early mornings when the Monterey Bay fog has had a chance to creep all the way south to us.  This fog typically burns off early in the day and doesn't return until well after midnight.  The most proximate ocean air intrusion comes through the Templeton Gap, where the Santa Lucia Range drops down from about 3000 feet high to around 2000 feet high.  That's still a significant hurdle for marine air to overcome, but many summer days the heat in the interior valleys of California is sufficiently intense to pull that marine air over the range and through the gap.  As the Templeton Gap is in the southwest quadrant of the AVA, it is that area, and to a lesser extent the area in the southeast, that gets the most afternoon cooling.  Our location at Tablas Creek, at the western edge of the AVA, gets less cooling than many areas significantly further east. 

The map below shows a typical afternoon temperature gradient, with cool parts of the AVA noted in blue and warm parts in red.  Note that while areas to the far east of the AVA are indeed quite warm, the principal gradient is just as much north-south as it is east-west.  You can see that Tablas Creek is neither particularly warm nor particularly cool, sheltered from that afternoon incursion of marine air but still at some altitude.  Click on the image below (and the rest of the images) to see them larger.

Paso Robles temperature gradient

Rainfall is a slightly simpler story, but still more complex than most accounts would suggest, having to do with altitude as well as proximity to the ocean.  Areas that are relatively high as well as relatively close to the ocean get the most rain, while lower areas and those farther inland get less.  And the differences can be dramatic.  This past weekend saw the much anticipated arrival of a series of storms which combined to drop 4.87 inches of rain on the weather station at Tablas Creek.  The town of Paso Robles received 1.25 inches, barely one quarter of what we received.  It's not always this dramatic, but our average annual rainfall of 28 inches is almost triple what vineyards on the Estrella River heartland of the Paso Robles AVA can expect.  Another map showing the overlays of the rainfall, with green areas receiving 25 or more inches of rain, brown areas less than 15 inches, and unshaded areas somewhere in between (data for this overlay comes from the Western Region Climate Center):

Paso Robles rainfall gradient

I tend to think that the data, as dramatic as it is, understates my experience of the regional variations in rainfall.  But still, the fact that you can drive 10 miles within the Paso Robles AVA and see rainfalls double (or half) where you started is remarkable.

Finally, the sections of Paso Robles with primarily calcareous soils.  I've written before about the benefits to viticulture of calcareous soils, and it was one of the principal criteria in our initial search for what would become Tablas Creek.  The map below shows the largest blocks of high-calcium soils (in yellow) though there are smaller outcrops in other parts of the AVA due to the complicated folding of soil layers thanks to our active tectonics (for more details on how the soils of our area formed, see my dad's post from last August Why We Are Where We Are).

Paso Robles calcareous overlay

There were three things that we were looking for when we first came up with the idea of a southern-Rhone-inspired project in California.  First was the right kind of climate, with enough heat and a long enough growing season to ripen some exceptionally late-ripening grapes and yet still moderated enough to let the more cool-loving Rhone grapes shine.  Second was enough rainfall to farm without needing to irrigate, which we felt was essential to allowing our grapevines to show a powerful signature of their location.  And third were calcareous soils.  Combining the high-rainfall, calcareous soils and mid-range temperature overlays from the above map produces one region, with Tablas Creek at its heart.  I don't think it's a coincidence that this is Paso Robles' Rhone heartland:

Paso Robles trifecta overlay

We didn't have this data available when we were looking for Tablas Creek; my dad and the Perrins spent their four-year search visiting vineyards, tasting wines, talking to farmers and looking at rocks.  But it's a testament to their perseverance and to their ability to ask the right questions that the data that has become available in the two decades since we bought our property has only served to further convince us that we chose the right place.

One final note: the shaded region above is broadly similar to the proposed Adelaida District in the Paso Robles sub-AVA petition that is undergoing TTB review as we speak.  These new AVA's, when and if they are approved, could be a powerful tool in helping explain to consumers, media and the trade just how a region they know by a single name can have such remarkable diversity inside it.