Ashland, Ore.—The Climate Prediction Center is calling for a greater likelihood of below-normal temperatures and below-normal precipitation through the end of February, according to Greg Jones, professor in the Department of Environmental Studies at Southern Oregon University. Longer term forecasts through early spring (February-April) are showing temperatures in the Pacific Northwest will likely be near normal to slightly below normal.

Jones included this information in his most recent weather report for winegrape growers in Oregon. He said the short- to long-term forecasts are consistent with historical West Coast climate data. “These conditions historically bring a slightly cooler than normal spring, with near-normal precipitation for the western U.S.,” he said.

How he does it
Curious as to how Jones develops these forecasts, which many in the industry deem quite accurate, Wines & Vines queried Jones about his methods.

We learned that grapegrowers on the West Coast are unusually favored in weather forecasting over those in most other parts of the world: The vast Pacific Ocean not only largely determines our moderate weather; it provides clear signals to what’s ahead. By contrast, the weather inland is heavily influenced by less-predictable continental forces.

Jones is both a climatologist and a meteorologist, so he studies both long- and short-term weather phenomena. To prepare his forecasts, he follows information from the four main meteorological agencies around the Pacific: from Chile, to Australia, Japan and the United States.

He then takes the short-term trends in the tropical Pacific and North Pacific and compares them to past conditions. He said that we have good weather information going back 100-120 years, and excellent data for the past 60 or so years.

Predictions for spring 2013
According to Jones’ most recent report, “Oregon experienced temperatures from 3°-4°F below normal,” in January, “while precipitation varied from 20% to 40% below normal. However, the snow-water equivalent remained at or above normal (98%-107%) in the watersheds feeding into Oregon wine regions after wet November and December.”

The report continued, “Both short and long-term weather/climate drivers for the western U.S. remain as they were in January. The North Pacific has remained in a cold phase similar to the past few years (cold Pacific Decadal Oscillation, or PDO), while the tropical Pacific has held its neutral state (some in the media call this La Nada [nothing] in analogy to El Niño and La Niña conditions).”

He said the Climate Prediction Center reported, “It is considered unlikely that an El Niño or La Niña will develop during the next several months, and El Niño/southern oscillation (ENSO)-neutral is favored through the Northern Hemisphere for the spring and early summer 2013.”

Weather cycles
The tropical weather varies in cycles of two to seven years, switching from conditions of El Niño and La Niña (the warm oceanic phase El Niño results in high air surface pressure in the western Pacific, while the cold phase La Niña accompanies low air surface pressure in the western Pacific).

By contrast, the north Pacific has warm and cold water cycles of about a decade.

Jones monitors conditions reported at seven or eight sources, and based on these patterns he issues predictions going forward two to 12 weeks.

Though Jones’ predictions focus on Oregon, he notes that conditions in California are flipped: “The fulcrum is between the border and Red Bluff; if Oregon is wetter and cooler, California is drier and warmer.”

Effects of climate change
Jones also has been involved in the discussion of climate change, and some have suggested his data show leading California wine regions may become too warm to produce top-quality fruit. The truth is more complex.

“There is no question that the climate today is warmer than 50 years ago,” he insists, “and that trend is likely to continue.”

One result may be that warm inland regions pull in more cold air to coastal valleys. And while some areas will simply get hotter, coastal areas may see another phenomenon: “The fog belt may be denser near the coast, but not extend as far inland.” That would have significant implications for growers in areas where the cooling fog’s impact changes.

He adds that the effects are likely to be very complicated; he cited two respected groups with differing prognostications on coastal weather as an example. “One predicted less coastal fog, one more.”

For those who’d like to sample his forecasts, Jones provides regular updates monthly or when the forecast shifts away from those given above. Email gjones@sou.edu to join the list.