Overall, we have had a good start to the 2013 winegrowing season here in the Petaluma Gap during April. Mean temperature and wind speeds have tracked historical averages under slightly drier and sunnier conditions.
Regional mean temperatures mirrored 10 year averages while experiencing higher highs and lower lows. April 2013 recorded mean daily temperatures that echoed 2009 and 2012. Solar radiation exceeded historical averages as well as levels seen in 2012 and 2011. Although April was a particularly sunny month in the Petaluma Gap, it was still surpassed by the amount of sunlight experienced in April 2009.
Humidity levels were lower than the historical average for the month of April. Only 2009 experienced slightly lower humidity during this period. Wind speeds were on par with 10 year historical and 2011 averages during April. 2012 and 2009 were slightly less breezy compared with the same period in 2013.
The following detailed comparisons attempt to place April 2013’s weather conditions in context with the exceptional vintages of recent past, 2012 and 2009, and the two previous vintage years. You can also download the complete report here.
The Petaluma Gap experienced mean daily temperatures that tracked to historical norms during the month of April. Diurnal temperature variations were a bit greater than average, however, as high and lows deviated from 10 year averages by 1.29 and -1.4˚F, respectively.
April mean daily temperatures were a single degree warmer than 2009 and only slightly cooler than 2012. Maximum average temperatures exceeded those of both 2012 and 2009. 2009‘s minimum April temperatures lagged 2013’s by 1.7˚F while 2012’s minimum temperature in April exceeded 2013 by 3.7˚F.
Compared with the past two April’s of 2012 and 2011, 2013 again recorded higher highs and lower lows.
Solar radiation exceeded averages by 3.8% for the month of April. Clear blue skies and lack of fog conditions were an indication of increased sunlight during the period.
April 2013 also surpassed 2012 and 2011 solar radiation levels by 49.0 Ly/Day or 10.3%. These sunny conditions were no match for those during April 2009 where sunlight levels were an additional 26 Ly/Day or 5.0% higher.
As a continuation from an unusually dry winter, the region recorded only 1.28” of rainfall during April or 19.2% below average. Additionally, humidity levels in April were 1.2% below the 10 year average.
April 2013 was also drier than 2012 and 2011 with an average of 3.3% less humidity. As dry as this April was, April 2009 was still 1.4% less humid.
There is seldom much to say about climatic conditions that are “average” except when considered in conjunction with other factors. The lack of winter rain combined with slightly increased evapotransporation (ETo) caused by the warm, sunny, dry and typically windy conditions in the region, could cause sooner depletion of available ground water and create the need for earlier irrigation.
April 2013 wind conditions mirrored those of 2011. 2012 and 2009 were only slightly less windy (5.8%) during April than this year. 2009 and 2012 recorded average winter rainfall and 2012 experienced slightly lower ETo during April.
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.