La Nina Dominates NOAA’s Winter Outlook | Idaho
PACIFIC NORTHWEST – Drought conditions in Washington, Idaho and Oregon are expected to improve this winter, but worsen across much of the West, the National Oceanic and Atmospheric Administration predicted Thursday (October 20).
NOAA has mainly based its outlook for December, January and February on a La Nina which is expected to prevail for a third consecutive winter.
La Nina winters are generally cold and wet in the northern United States, but warm and dry in the southern United States. The effects of La Nina are most pronounced in the Lower 48 in the far north or far south.
For regions in between, such as southern Oregon, southern Idaho, and northern California, La Nina winters can be mild, severe, or average. Climatologists consider it a toss-up.
Drought conditions across much of eastern Oregon and northwestern California are expected to improve, but not disappear, forecasters say. The drought will likely be erased in Washington, northern Oregon and much of Idaho.
Washington irrigators are among the biggest beneficiaries of La Nina. According to NOAA, the ingredients of a heavy snowpack, below average temperatures and above average precipitation are likely for the state.
Winter will vary widely along the West Coast, said Jon Gottschalk, head of the forecasting branch of the Climate Prediction Center.
“As you move north into Washington, we think there’s more likelihood of above normal precipitation there,” he said.
The drought is likely to worsen in southern California, the Southwest and the Great Plains, and expand in southeast and southern Texas, forecasters said.
A third consecutive La Nina winter is rare. Since 1950, it has happened twice more. The last time was the winter of 2000-01. La Nina was weak and Washington’s snowpack was below average.
The previous time, the winter of 1975-76, the Nina was strong and the snow cover above average.
This La Nina will likely be a “moderate event,” but the strength of a La Nina doesn’t adjust the forecast, Gottschalk said.
“With La Ninas, to be honest, there’s not a lot of predictability in the impacts (based on) whether they’re low, moderate or high,” he said.
A hot, dry summer and fall brought drought to Washington after an extremely cold and wet spring.
About 61% of the state was in drought on October 20, the US Drought Monitor reported. Much of western Washington was in a “severe” drought.
Drought conditions are more widespread and deeper in Oregon. About 80% of the state is in a drought. Parts of eastern Oregon are experiencing “extreme” or “exceptional” drought.
The region should soon be relieved, said NOAA drought forecaster Brad Pugh.
“Right now we’re seeing a major pattern shift happening near the west coast,” he said. “It looks like a much wetter pattern for Washington, Oregon from late October through at least early November.”
La Ninas is triggered by below average sea surface temperatures in the Pacific Ocean. El Ninos is caused by warm seas. Washington’s 2015 snowpack was during an El Niño.
La Nina influences the weather for an entire season. Shorter-term events, such as “atmospheric rivers,” will also influence whether a region has a wet or dry winter, climatologists said.
Ocean temperatures in the North Pacific could also affect seasonal weather patterns, they said.