Weather Monitoring

We monitor key weather variables (temperature, humidity, rainfall) in the vineyard for 4 purposes:

  1. To estimate the anticipated picking date early in the season in order to plan and schedule picking. This is done by tracking temperature in hourly intervals and calculating / graphing Growing Degree Days

  2. To estimate the vulnerability of the vines to diseases, particularly mildew in order to schedule spraying with fungicides. This is done by tracking a Mildew Pressure Indicator derived from temperature and humidity.

  3. To evaluate the need for irrigation.

  4. To provide a narrative for the weather at the end of the year to characterize the grapes and resulting wine

We started collecting weather data consistently only in late 2012. For this, we use a Vantage Pro2 weather-station from Davis (http://www.davisnet.com/weather/products/weather_product.asp?pnum=06152) to collect rain, temperature and humidity data.

Growing Degree Days

Growing Degree Days (GDD) measure the warmth plants have been exposed to over a season. The assumption is that grapes develop commensurate with the temperature multiplied by the time they are exposed to that temperature. The temperature needs to be above 55°F to start counting and is maxed out at 95°F. In simple terms, 1 GDD is accumulated when a plant is exposed to 58 °F for 8 hours (i.e. 58-55) * 1/3rd day). To calculate GDDs with reasonable accuracy, we need long histories of consistent hourly temperature readings and compute the sum of Growing Degree Hours divided by 24. Reliable data is available free at the National Oceanic & Atmospheric Administration (NOAA)’s website http://www.nc°C.noaa.gov/. For temperature data go to http://gis.nc°C.noaa.gov/map/viewer/#app=cdo&cfg=cdo&theme=temp&layers=1, select a location and download the data for the required time period.

Why then do we need our own weather station?

Long, high-quality time series of climate data is generally collected at airports only. We downloaded hourly data for the nearest airport (San Jose Airport, SJA) for 12 years and then computed the Cumulative GDDs. The graph on the left shows the result. The little red squares indicate the dates each year when we picked them. Note, at San Jose Airport, approx. 15 miles away, CGDDs reach somewhere between 2000 and 2400 by the time we pick at Chateau Hetsakais. If the San Jose Airport CGDDs measured ripeness accurately, then all red squares should theoretically lie on a horizontal line. To look at this more closely, we computed the difference of each year’s CGDD curve with the average of all 12 years. The result is shown in the graph in the middle.

Again, the red squares should lie on a steeply sloping line, because we would expect to have picked earlier in relatively warmer years and later in relatively cooler years. But it does not look like we did. There could be 3 different reasons for this “disconnect”: Either the GDD theory is not valid (I doubt it), or we did not pick at the same level of ripeness each year (possible), or the weather is different at SJ Airport when compared to our vineyard (probable).

To test the latter we checked the correlation of average daily daytime and nighttime temperatures between San Jose Airport and temperatures collected at our vineyard (only available for 2013. This graph on the right shows the result. Clearly, the relationship is not very tight with linear regressions showing R-Squares of less than 0.95. My conclusion is that we cannot rely on historical data collected at San Jose Airport. Instead, we need to collect our own data history. This is why we need our own weather station.

Data Management

We purchased a Vantage Pro2 weather-station from Davis and collected our own hourly weather data since mid-2012.

At this juncture, we only track and analyze hourly temperature and humidity data. In the future, we plan to collect and analyze a wider range of data, including humidity, rainfall, UV intensity, etc. From the hourly data we compute:

We monitor key weather variables (temperature, humidity, rainfall)  in the vineyard for 4 purposes:

  1. To estimate the anticipated picking date early in the season in order to plan and schedule picking. This is done by tracking temperature in hourly intervals and calculating / graphing Growing Degree Days

  2. To estimate the vulnerability of the vines to diseases, particularly mildew in order to schedule spraying with fungicides. This is done by tracking a Mildew Pressure Indicator.

  3. To evaluate the need for irrigation.

  4. To provide a narrative for the weather at the end of the year to characterize the grapes and resulting wine

We started collecting weather data consistently only in late 2012. For this we use a Vantage Pro2 weather-station from Davis  to collect rain, temperature and humidity data.

 

Growing Degree Days

Growing Degree Days (GDD) measure the warmth plants have been exposed to over a season. The assumption is that grapes develop commensurate with the temperature multiplied by the time they are exposed to that temperature.  The temperature needs to be above 55°F to start counting and is maxed out at 95°F.  In simple terms 1 GDD is accumulated when a plant is exposed to 58 °F for 8 hours (i.e. 58-55) * 1/3rd day). To calculate GDDs with reasonable accuracy, we need long histories of consistent hourly temperature readings and compute the sum of Growing Degree Hours divided by 24.  Reliable data is available free at the National Oceanic & Atmospheric Administration (NOAA)’s website . For temperature data go to this website, select a location and download the data for the required time period.

 

Why then do we need our own weatherstation?

Long, high quality time series of climate data is generally collected at airports only. We downloaded hourly data for the nearest airport (San Jose Airport, SJA) for 12 years and then computed the Cumulative GDDs. The graph on the left shows the result.  The little red squares indicate the dates each year when we picked the.  Note, at San Jose Airport, approx. 15 miles away, CGDDs reach somewhere between 2000 and 2400 by the time we pick at Chateau Hetsakais. If the San Jose Airport CGDDs measured ripeness accurately then all red squares should theoretically lie on a horizontal line. To look at this more closely, we computed the difference of each year’s CGDD curve with the average of all 12 years. The result is shown in the graph in the middle. 

Again, the red squares should lie on a steeply sloping line, because we would expect to have picked earlier in relatively warmer years and later in relatively cooler years. But it does not look like we did. There could be 3 different reasons for this “disconnect”: Either the GDD theory is not valid (I doubt it), or we did not pick at the same level of ripeness each year (possible), or the weather is different at SJ Airport when compared to our vineyard.

To test the latter we checked the correlation of average daily daytime and nighttime temperatures between San Jose Airport and temperatures collected at our vineyard (only available for 2013. This graph on the right shows the result. Clearly, the relationship is not very tight with linear regressions showing R-Squares of less than 0.95. My conclusion is that we cannot rely on historical data collected at San Jose Airport. Instead we need to collect our own data history. This is why we need our own weatherstation.

 

Chateau Hetsakais weather data

We purchased a Vantage Pro2 weather-station from Davis and collected our own hourlly weather data since mid 2012.











ALL Weather Data.png

At this juncture, we only track and analyze hourly temperature and humidity data. In the future, we plan to collect and analyze a wider range of data, including humidity, rainfall, UV intensity, etc. From the hourly data we compute:

  • Average temperature between 9am & 9 pm (day-time)

  • Average temperature between 9pm & 9am (night-time)

  • Average humidity between 9am & 9 pm (day-time)

  • Average humidity between 9pm & 9am (night-time)

  • Highest and Lowest temperatures for the day

  • Cumulative Growing Degree Days with 55dF and 95dF cutoff points

  • Average data for 2012 through 2017 for every day of the year

  • 7-day moving averages of all the above

Then we enter this data into the “WeatherData” table of the database. Above is a screenshot of the day’s data for August 6, 2018. The following screenshot of the “Weather”-tab in the “REVIEW: VineyardActions”-layout illustrates how we use the weather date to summarize weather conditions during the growing season.

REVIEW VinayardActions Weather.png



Previous page: Pest Management
Top of this page: Go
Next Page: Winery OVERVIEW
Last updated: January 2, 2019