Winegrowing conditions throughout the month of July experienced higher humidity under steady wind speeds. Mean temperatures matched, while sunlight levels lagged, historical averages.
Regional average and high temperatures fell back in line with 10 year averages while also experiencing higher lows. July 2013 recorded diurnal temperature variations that were lower than historical and recent averages but similar to 2009. Solar radiation trailed historical averages and all years under review during July. A daily marine layer that lingered until midday prevented greater accumulations of sunlight to reach the canopy, potentially slowing fruit maturation.
Humidity levels were again higher than the historical average for the month of July due to prolonged daily marine layers. In recent years, only 2011 humidity levels exceeded levels that we experienced this July. Wind conditions remained steady in July and did not decrease as is typically experienced as the growing season progresses. Only 2009 was windier compared with this period in 2013.
The following detailed comparisons attempt to place July 2013’s weather conditions in context with the exceptional vintages of recent past, 2012 and 2009, and the two previous vintage years. You can download the complete report here.
The Petaluma Gap experienced mean daily and high temperatures that fell back to historical norms of around 61˚F during the month of July. Diurnal temperature variations, however, were 1.73˚F lower than average, as low temperatures were above 10 year averages by 2.14˚F.
July mean daily temperatures were on par with 2012 and 2011 but slightly surpassed those of 2009 by 1.4˚F. Maximum average temperatures matched 2012 but were greater than those of 2011 and 2009 by an average of 1.7˚F.
2013 minimum average temperatures also exceeded all years under review by more than 2˚F. As a result, combined with average daily and maximum temperatures, diurnal variations were 2-3˚F lower in July.
Solar radiation levels of 594 Ly/Day were 19.8 Ly/Day or 3.2% below average for the month of July. Throughout most of the month we experienced a marine layer that lingered until almost midday, diminishing the total amount of sunlight reaching the vines.
July’s sunlight levels were again lower than those seen in 2012 by 52 Ly/Day or 8.2%. 2011 and 2009 also saw higher levels of solar radiation compared to this year by 35 Ly/Day (6.0%) and 67 Ly/Day (11.5%), respectively.
Humidity levels continue to outpace historical averages by 3.2% (77%). The extended marine layer that caused lower temperatures and diminished sunlight is also responsible for increased humidity in the region.
July humidity was only surpassed by levels achieved in 2011. 2012 was 6.5% drier and 2009 only slightly drier at 1.3%.
The increased humidity, combined with lower temperatures, meant that evapotranspiration during July was 2.4% less than the previous 10 year average, presumably lowering irrigation demands.
Historically, wind speeds slow as the growing season progresses. This July, however, wind speeds throughout the region remained steady and were only 4.5% lower than the previous 10 year average.
July 2013 wind conditions surpassed those of 2012 by 5.9% and matched 2011. 2009 was 11.1% windier than July of this year.
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.