Wet weather gives way to helpful heat

After a drizzly, humid weekend, grape growers are grateful for a
forecast of above average temperatures through the end of the
month.
“This weather forecast is excellent. We need both the heat and
sun,” said Nick Frey, President of the Sonoma County Winegrape
Commission.
The damp weather and middling temperatures—prime weather for
mold growth—put the county’s grape harvest at risk of mildew and
bunch rot. In five out of six growing regions, the powdery mildew
stress was designated “severe” by the Western Weather Group.
Weekend rainfall varied between trace amounts and one tenth of an
inch depending upon microclimate, and the extent of the damage to
local vineyards still remains to be seen.
Despite the Southern Oscillation Index confirming an official
state of La Niña, which typically means early rains followed by a
dry later season, the early fall forecast is for sun.
“Rainfall wise, there’s nothing to show a system coming in the
next week or two that would scare the growers with a decent
rainfall. Actually, for the next week and a half, most models
haven’t shown any systems coming into the county at all,” said Matt
Wanink, a Sonoma County forecaster for the Western Weather
Group.
“As we head into October, the global models that we use can
sometimes become more flaky because of the seasonal changes. But
the most recent runs have been consistently showing a ridge over
California and keeping temperatures warm, which I’m sure growers
are happy about,” Wanink said.
Temperatures in warmer microclimates like Alexander Valley are
expected to soar into the upper nineties over the weekend. Cooler
microclimates can expect temperatures in the eighties and low
nineties. But even with the heat, it may take several weeks until
the county’s grape harvest is complete.
“Alexander Valley is as far ahead as anyone, but the harvest has
been slow so far,” Frey said. “We’re only around 5, 6, 7 percent of
harvest. Sure, it’s starting, but we’re nowhere near the peak.”