As Northwest wine country officially enters summer, the forecast for the region signals a return to warmer-than-average conditions and growing concern about the extended drought conditions in some corners.
Gregory V. Jones, director of the Evenstad Center for Wine Education at Linfield College and the Evenstad Chair in Wine Studies for the McMinnville, Ore., school, pointed out that growing degree days for Southern Oregon are tracking ahead of the historically hot 2015 vintage. Pinot Noir producers in the Willamette Valley and vineyards in the Walla Walla Valley began June closer to the 30-year normal.
“The June through August seasonal forecast for the western U.S. continues to point to the likelihood of warmer than average conditions into the heart of summer,” Jones wrote in his Weather and Climate Summary and Forecast for June 2020. “The overall precipitation outlook continues the drier than average conditions for much of the PNW and northern California, and near average elsewhere in the West.”
Jones, widely viewed as the North American wine industry’s leading expert on climate research, pointed out that “May flip-flopped from unseasonably warm in the first ten days of the month, to average or cooler than average during mid-month, back to a relatively warm last ten days, ending overall warmer than average.”
In some areas of the Northwest, rains produced 110 to 250% of the normal precipitation for the month of May.
“There was above-normal precipitation in portions of Northwest during May, however moderate to extreme drought conditions remain over much of California, Oregon, and central to eastern Washington,” he wrote. “Conditions are expected to continue through August.”
Columbia Valley begins June a week behind average
Overall, those rains and cool temperatures left the Columbia Valley about one week behind the recent average when June began, Jones wrote.
At the weather station he charts In the Walla Walla Valley town of Milton-Freewater, Ore., there were 414 growing degree days through May 31. At the same stage in the record-hot vintage of 2015, there were 574 cumulative GDD. The 1981-2010 average was 395.
Washington State University’s AgWeatherNet logs growing degree days via its 177 stations across the state as well as parts of Oregon and Idaho.
Through May 31, there were 531 growing degree days recorded at the East Mattawa Station on the Wahluke Slope. A year ago, it charted 623 GDD. During the 2015 vintage, it stood at 586 when June began.
At the Benton City station near Red Mountain, there were 598 GDD recorded. A year ago, it read 650 GDD. In 2015, there were 654 GDD.
On Snipes Mountain in the Yakima Valley, there were 558 GDD registered. A year ago, the accumulation stood at 601 GDD. During the blistering 2015 season, it was 635.
At Phinny Hill in Klickitat County’s Horse Heaven Hills, that station measured 515 GDD. In 2019, it read 617. Back in 2015, before the temperatures really began to climb in the Columbia Valley, there were 550 heat units.
Along the Columbia Gorge, Husum notched 296 GDD. A year ago, it stood at 348. The Pullman school’s station in Woodinville collected 278 GDD, compared with 291 GDD last year. Back in 2015, it received 317.
In McMinnville, the heart of Willamette Valley’s Pinot Noir territory, there were 322 growing degree days — which is behind the 2015 mark of 362. However, data from the two Southern Oregon sites used in his report were well above the 2015 recordings.
In Roseburg, home to the Fault Line Vineyards and Abacela Winery established by his father, Earl Jones, there were 562 GDD compared to 507 of three years ago. In Medford, not far from the Southern Oregon University campus where Greg Jones worked for two decades, the station charged 584 GDD. In 2015, they measured 549.
“All four locations are above the 1981-2010 normals for the months of April and May, however eastern Oregon (Milton-Freewater and the Walla Walla region) are running only 5% up while other locations are 25-60% up,” Jones noted. “Similarly, compared to the average of the last 15 years for the sites, Medford, Rosburg, and McMinnville are 10-30% up while Milton-Freewater is 10% down. Compared to 2019, Roseburg and Medford are 1-5% up during the same period in 2020 while McMinnville and Milton-Freewater are running 9 and 32% below values seen in 2019, respectively.”
Spring challenges for vines, cherries
The precipitation in recent weeks meant vineyard managers could not let their guard down on spraying for powdery mildew. Meanwhile, those in the cherry industry have experienced a double blow as the cool and wet opening half of June came on the heels of “little cherry disease” in orchards throughout the Northwest. A number of the Columbia Valley’s leading grape growers are diversified farmers, and their holdings include cherries.
On top of that, vineyard managers will likely face more nighttime humidity this summer, which can affect the natural acidity in grapes.
Off the coast, Jones shared that the North Pacific remains warm with sea surface temperatures 2°F to nearly 4°F warmer than average.
“Ocean temperatures are also now well above average along the coast from Alaska to Baja California indicating that upwelling has slowed,” he wrote. “This is likely due to a decline in the overall wind field over the eastern Pacific. Overall, the North Pacific has warmed over a relatively large part of the basin, and with the warmer waters, we are seeing elevated humidity and higher nighttime temperatures over the West.”