Winegrowing conditions throughout the month of May were a continuation of the drier and sunnier conditions experienced in April. Again, mean temperatures and wind speeds have tracked historical averages.
Regional mean temperatures mirrored 10 year averages while experiencing higher highs and lower lows. May 2013 recorded mean daily temperatures that fell between those of 2009 and 2012. Solar radiation exceeded historical averages as well as levels seen in 2011 and 2009. Although May was a particularly sunny month in the Petaluma Gap, it was still slightly surpassed by the amount of sunlight experienced in May 2012.
Humidity levels were lower than the historical average for the month of May. May 2012, 2011 and 2009 all experienced higher humidity levels than May 2013. Wind speeds remained on par with 10 year historical averages and with 2011 averages during May. 2012 and 2009 were again slightly less breezy compared with this period in 2013.
The following detailed comparisons attempt to place May 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 May. Diurnal temperature variations were again a bit greater than average, however, as high and lows deviated from 10 year averages by 1.44 and -1.45˚F, respectively.
May mean daily temperatures matched those of 2009 and were a degree warmer than 2012. Maximum average temperatures slightly exceeded those of both 2012 and 2009. 2013 minimum temperatures equaled those of 2012 but were 3.3˚F cooler than 2009.
May 2013 experienced similar diurnal temperature variations to 2012 and greater variations than 2011.
Solar radiation exceeded averages by 27.3 Ly/Day or 3.8% for the month of May. Clear blue skies and lack of fog conditions were an indication of increased sunlight during the period.
May 2013 experienced only slightly diminished solar radiation levels than 2012 (-22 Ly/Day, -3.4%) but surpassed both 2011 (69 Ly/Day, 11.8%) and 2009 (32 Ly/Day, 5.5%) levels.
Following a particularly dry April, May continued to experience arid conditions with humidity levels of 69% or -7.4% below historical averages.
The region experienced a negligible amount of rainfall on May 27th. 2009 recorded average rainfall for May while 2013 and 2012 recorded negligible precipitation in May.
May 2013 was also drier than 2012, 2011 and 2009 with an average of 9.2% less humidity. These excessively dry conditions increase evapotranspiration requiring more water resources to irrigate the vines.
The lack of rain in April and May combined with slightly increased evapotransporation (ETo) caused by the warm, sunny, dry and typically windy conditions in the region, increased the need for adequate irrigation.
May 2013 wind conditions mirrored those of 2011. 2012 and 2009 were less windy by -7.3% during May than 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.