"Just for the record, the weather today is calm and sunny..."

"but the air is full of ..." OK, no need to complete Chuck Palahniuk's quote because the truth is in the numbers. Besides being calm and sunny, the air was also warm and dry in the vineyard last month. Instead of boring you to tears by making your wade through another weather post, I created this 2 Minute Video report to bore you in half the time. Pretty pictures, cooler graphs, half the calories.


Mean daily temperatures of 56.9˚F in May were on par with those seen in 2013 and 1.3˚F warmer than the previous 10 year average. Maximum temperatures reached 74.1˚F (2.5˚F higher than 2013 and 4.9˚F higher than average) while minimum temperatures dipped to 39.6˚F (2.6˚F lower than 2013 and 3.3˚F lower than historical norms). 

Last month's higher highs and lower lows created diurnal variations of 34.5˚F (5.1˚F higher than 2013 and 8.2˚F higher than average).

Diurnal variation relates to the daily temperature differences between the highs and the lows. Higher variations create conditions for high sugar production while preserving more natural acidity.

Although mean daily temperatures were equal to or higher than the past, we are still slightly behind in growing degree days than at this time last year.

Growing degree days measures heat accumulation and is used to predict rates of grape development. Measured from April through October, the Sonoma Coast's maritime climate averages 2,185 degree day units (GDUs).

Solar Radiation

All things considered, last month's 647 Ly/Day amounted to a sunnier month than in the past. May saw a 5% increase in sunlight over last year and a 10.9% increase over historical averages. This would indicate that May experienced less of an influence from our typical morning and evening marine fog layers.


Wind conditions in May were typical to this time of year with only slight decreases compared to 2013 and 10 year historical averages of 2.4% and 4.1%, respectively.


Compared to April, May was considerably drier. 70% average relative humidity was a mere 1.0% decrease compared to last May but 4.8 percentage points compared to historical averages for May. More sun, higher temperatures and steady winds equal lower humidity and less fungal disease pressure.