subscribe: Posts | Comments      Facebook      Email Steve

Understanding temperature data? Not so easy!



One of the toughest parts of my job—of any wine writer’s job, actually—is finding reliable, historic data on which to base conclusions about terroir.

Lord knows, we have endless discussions about terroir, yet most of them are based on anecdotal information and as we all know anecdotes are not reliable. They may be interesting, they may be well-meaning on the part of the teller, and they may even be true. Yet there’s nothing like accumulated, provable data to underscore a scientific claim.

Having been in this business for a long time I can’t tell you how often I’ve been given directly conflicting info by winemakers who often couldn’t agree on the characteristics of their region’s terroir even when their vineyards were right next to each other! Or, along similar lines, they couldn’t agree on the qualitative aspects of the wines from the appellation they shared. Needless to say, this makes the wine writer’s job more difficult, so in the end, we’re forced to come to our own conclusions—for which the winemakers who couldn’t agree in the first place then criticize us. Sigh…

A nice example of my current challenge is to determine, precisely and clearly, the temperature and climate differences between the Santa Maria Valley and the Santa Rita Hills, especially for growing Pinot Noir. The two AVAs are, of course, close together. Both are open to the west winds from the Pacific; both are east-west-running valleys. Is one cooler than the other? How does one define “cooler”? This is where the tough part of my job kicks in. Where is the data? Who controls it? Is it a government agency, like NOAA? Do individual vineyards have weather sensors that could tell us? Is that data proprietary or is it sharable? Over how many years does the data span? I don’t want data only from a single year; to be credible the data should span multiple years. Who’s been measuring degree days or daytime and nighttime lows for a decade? How long does the high temperature remain high during the day—for 30 minutes? An hour? Both AVAs are long, in an east-west direction: how much does the daily high temperature vary as you move inland? A degree a mile, as is commonly cited? What part does elevation play (both AVAs contain significant hills). This only begins to describe the complexities. As the great Saintsbury winemaker David Graves notes, “What do you mean by cooler? Hours above or below a threshold? Nighttime lows? Daytime highs? The period between veraision and harvest? Bloom-harvest? And what role does relative humidity play?” For the wine writer these are difficult things to determine, but they seem central to me, if you’re trying to pick apart the differences between neighboring appellations. After all, if an appellation means anything to begin with, it consists of these very complexities and ambiguities.

Yet if a writer wants really to tackle issues of terroir, these data points need to be accumulated. The trouble is, where are they?

It’s hard work, which is why there are so many shibboleths and myths in this business. Who’s got the time to research this stuff, or even to figure out how to begin? So, too many wine writers look up something Matt Kramer, or Oz Clarke, or Steve Heimoff or Larry Walker or somebody else once said, and repeat it, as though it were the gospel truth. Which it might or might not be. It’s not that any of these individuals would deliberate misstate something (Heaven forbid!) but that they might have got it wrong to begin with, without knowing it and without having subsequently been corrected.

Anyhow, this is one reason why the more I last in this business the less I trust “the conventional wisdom.” Still, understanding appellations is as central to my job as breathing is to life. I hope to just be able to contribute some small part to it that will stand the test of time.

  1. Steve,

    Again, you hit the nail on the head. The gradual nature of climatic change makes defining a climate difficult. Where does one climate type start and the other end? As far as data, let me add in the challenge of “Are the data reliable?” The first thing I do with any weather data I get is thoroughly investigate them for holes. Batteries run out, equipment breaks, information gets erased, clocks get set wrong. A data set missing three weeks in the middle of July and a week in the middle of September is almost useless. Whenever possible, I also try to see the location of the weather station to make sure it is not being influenced by poor placement.

  2. Bob Henry says:

    If Pinot Noir is the “transparent” grape that so many of its admirers and proponents say it is, then it should reflect the terroir it comes from.

    I don’t expect Sonoma Pinots to taste like Napa Pinots. Or Mendocino or Anderson Valley Pinots. Or Santa Cruz Mountain Pinots. Or Monterey Pinots. Or Gavillan Mountain Pinots. Or Paso Robles Pinots. Or Santa Barbara County Pinots.

    The producers in each region have adopted and propagated different clones. Different planting densities. Different growing practices. Different picking practices based on brix or “physiological ripeness.” And different fermentation practices (e.g., wild yeast versus inoculated yeast).

    That matrix of decisions consequently leads to a continuum of styles.

    Beyond temperature/climate considerations, we now for the first time have to think about the soil and the “critters” that inhabit it.

    “Sequencing Study Lifts Veil on Wine’s Microbial Terroir”


    “Microbes May Add Special Something to Wines”


    “Dishing the dirt” on dirt . . .



  3. Bryan Vais says:

    Steve… FWIW, when I need to research temperature data on AVAs I use the online resource provided by Utah State University here.

    The user interface is map-centric but quite dense, so you may want to find someone adequately geeky to help you. From this site you can pull historic weather data collected on a daily basis that includes Hi-Lo temps, rainfall, etc., dating back decades. The data points captured and dates covered vary station by station.

    A quick drill down shows data points for both Santa Maria public airport and Lompoc, dating back to the ’40s. Obviously these are not centered in the AVAs of interest, but may provide enough to show relative differences if plotted alongside each other. Good luck!

  4. Bob Henry says:


    The Lompoc report:

    Monthly Mean Temperature in °C [so you need to convert to °F, if desired]

    Period of record: 1917-2014


    And here’s the Santa Maria public airport report:

    Monthly Mean Temperature in °C [so you need to convert to °F, if desired]

    Period of record: 1917-2014

    ~~ Bob

  5. Bob Henry says:


    While my 12:45 am comment awaits moderation, here is an addendum.

    The monthly mean temperature reports for Lompoc and Santa Maria offer these functions:

    Export this report as a spreadsheet (CSV):
    Click here for instructions on saving this report as a PDF document.
    Click here for instructions on printing.

    The first is of greatest utility, establishing a spreadsheet for each site.

    Tell K-J’s intern to “have fun!” juxtaposing the numbers and calculating the “deltas.”

    ~~ Bob

  6. Bob Henry says:

    Here are the deltas . . .

    Citing the monthly mean temperature, Lompoc is warmer than Santa Maria.

    Example: In the calendar month of January (on average), Lompoc is +0.90°C warmer than Santa Maria.

    Annually (on average), Lompoc is +0.50°C warmer than Santa Maria.

    MONTH: Jan Feb Mar Apr May Jun
    DELTA: +0.90°C +0.80°C +0.80°C +0.70°C +0.50°C +0.30°C

    MONTH: Jul Aug Sep Oct Nov Dec Annual
    DELTA: +0.00°C +0.10°C +0.04°C +0.50°C +0.50°C +0.70°C +0.50°C

  7. Bob Henry says:

    Here’s a researcher who might have answers to your questions about Santa Maria versus Santa Rita Hills:

    Excerpt from the Santa Rosa Press Democrat “Main News” Section
    (August 4, 2008, Page A1ff):

    “Mendocino the New Napa?;
    Changing weather patterns may make Ukiah Valley better for grapes”


    By Mike Geniella
    Staff Reporter

    “. . . nationally known climatologist Gregory Jones of Southern Oregon University . . . compiled, analyzed and published findings from a study of 50 years of Wine Country temperature data.”

    Contact info:

    Continuing on the subject of dirt …

    From The New York Times Magazine
    (May 6, 2007, Page Unknown):

    “Talk Dirt to Me”


    By Harold McGee and Daniel Patterson

    From the Soil Science Society of America website:

    “From Soil Profiles to Flavor Profiles: Is There a Connection When it Comes to Winemaking?”


    By Caroline Schneider
    Science Writer

  8. Bob Henry says:


    The UC Davis Robert Mondavi Institute for Food and Wine Science’s Spring 2006 international conference titled “Terroir 2006” featured a keynote address titled “You Said Terroir? Approaches, Sciences, and Explanations.”

    (Stonestreet was a corporate sponsor.)


    Excerpt: “The conference keynote speaker was Warren Moran, professor emeritus of geography at the University of Auckland (New Zealand), who addressed the various approaches, science, and explanations of terroir.”

    Worth getting a copy.

    ~~ Bob

  9. Bob Henry says:


    The presentation is password protected:

    (I have a hard copy. I cannot locate any version “floating” around on the Web.)

    The Wine Enthusiast write-up on the international conference:


    The wine world’s most elusive yet most compelling concept—the role of terroir—got a thorough workout in mid-March during three days of panels and presentations at the University of California at Davis. Organized by several Davis academic departments and the new Robert Mondavi Institute for Wine and Food Science, Terroir 2006 brought together geologists, plant physiologists, winemakers, writers and marketers from seven countries for serious talk about the taste of a place (and the occasional glass of wine).

    Some useful points emerged by consensus:

    The distinction between macroterroir or macroclimate (Napa Valley), mesoterroir (the Stags Leap District within Napa) and microterroir (a single vineyard within Stags Leap). All three frames of reference are useful, but not interchangeable.

    Global warming has major and perhaps ominous implications for terroir-based wines. If the special character of a wine region depends on a narrow band of climate, all traditional bets may be off. Sweden—yes, Sweden—is investing heavily in grapevines, just in case.

    Whatever terroir contributes, it’s losing ground to technology-driven winemaking in the world market.

    Controversies surfaced in abundance, though not always directly:

    Does terroir include only the physical characteristics (soil, climate, etc.) of a growing site, or human factors (winemaking practices, cultural traditions) as well? Keynote speaker Warren Moran of the School of Geography and Environmental Science at the University of Auckland, New Zealand argued that terroir is a social category, constructed over time by people who manage a particular geography; other speakers were emphatic about the primacy of natural factors.

    UC Davis plant physiologist Mark Matthews woke everyone up on day three by maintaining that the concept of terroir is based on pre-scientific notions of how vines work—for example, that they draw their essential characteristics from the soil in which they are rooted, whereas modern plant science tells us wine flavor compounds are created inside the grape berries.

    Writer Karen MacNeil offered the most delicious speculation: What if all the planet’s truly great wine terroirs have yet to be discovered?

    Materials from the conference are posted at
    —Tim Patterson

Leave a Reply


Recent Comments

Recent Posts