Spring has sprung amid a daunting drought

Now that spring is finally here, it's time to kick off another growing season with our April Winegrowing Update. But first, a word about how the drought is affecting us here in the Petaluma Gap within the Sonoma Coast.

Winter Rainfall

Roughly speaking, we measure the rains that fall during the "rainy season" here in Sonoma from Oct/Nov of the previous year until April/May of the harvest year. Over the last 10 years, the average rainfall here in the Petaluma Gap has been around 21 inches. From October 2013 through April 2014, we have only received 16" (-24% of the average). This wouldn't be too much of a concern if not for the most recent shortages in 2012 and 2013 of -28% and -32%, respectively.

Ten years is hardly sufficient to jump to the conclusion that our climate is becoming more arid, but we should all be in the habit of conserving water where we can. Maybe it's time to replace those irrigated lawns with a rock garden.

April Winegrowing Update

Winegrowing conditions throughout the month of April experienced higher humidity under slightly diminished wind speeds. Mean temperatures exceeded while sunlight levels matched historical averages.

Regional average temperatures exceeded 10 year averages due in part to day time highs hitting the mid 80's during the last week of the month. April 2014 recorded diurnal temperature variations that were higher than historical and recent averages. Solar radiation mirrored historical averages while slightly trailing 2013 during April. Early morning fog and patches of rainstorms inhibited sunlight accumulation.

Due also in part to early morning fog and welcomed rainstorms, humidity levels were slightly higher than average and during this period last year. Wind conditions were slightly lower than average.

The following detailed comparisons attempt to place August 2013’s weather conditions in context with historical averages.


The Petaluma Gap experienced slightly higher mean daily temperatures in April than it had in 2013 and over the last 10 years. Bolstered by temperatures that reached the mid 80's during the latter part of the month, mean temperatures were almost a full degree higher than last year and 1.4˚F higher than the previous 10 year average. While average low temperatures mirrored historical averages for the region, high temperatures surpassed norms by 3.6˚F.

Sonoma Coast / Petaluma Gap April Winegrowing Temperature

Solar Radiation

At only 5.5 Ly/Day (or a mere 1.1%) higher than average, the total amount of sunlight in the region effectively maintained normal levels. However, these levels were 25 Ly/Day or 4.6% lower than experienced during April of 2013 due in part to the fact we saw over 3" more rain in 2014 than we did during the same period in 2013.

Sonoma Coast / Petaluma Gap April Winegrowing Sunlight


Wind speeds in April were considerably lower than 2013 and the previous 10 year average by 13.3%. Neither the abundance or lack of airflow is not a major concern this early in the growing season. 

Sonoma Coast / Petaluma Gap April Winegrowing Wind


April was a modestly "wet" month with average relative humidity 5.4% higher than 2013 and 3.3% higher than historical averages. Similarly to the slightly diminished sunlight this month, the higher average relative humidity was partly due to the increased periods of rain that we experienced in April.

Sonoma Coast / Petaluma Gap April Winegrowing Humidity


Although of supreme importance, weather, in and of itself, is only a single variable in a wine growing season. The resulting fruit quality when it arrives at the winery is determined by a myriad conditions such as timing of weather events, site micro-climates, geography/orientation, training/trellising, fruit set, canopy management, etc etc etc. 

This report is based on Petaluma Gap regional weather data obtained from the California Irrigation Management Information System (CIMIS) Petaluma East Station (144) and is meant to characterize general growing conditions for the region. It should not, in any way, be construed to represent the growing conditions for any one particular vineyard site.