National Oceanic and Atmospheric Administration
La Nina conditions, heralding cool and wet weather in the Pacific Northwest, are expected to persist all winter, the National Oceanic and Atmospheric Administration reported Thursday.
Climatologists, in a new three-month outlook, noted that sea-surface temperates are below average along the equator off the coast of South America. The temperatures aren’t likely to rise to normal until mid- or late spring, according to NOAA’s Climate Prediction Center.
The cool ocean, or La Nina, and its affect on the atmosphere shaped the seasonal forecast. The report was similar to last month’s three-month outlook, Conditions favor snow accumulating in the mountains to supply Northwest irrigators.
NOAA predicted below-average temperatures and above-normal precipitation in Washington, most of Western Oregon and the Idaho panhandle.
To the immediate south — central Idaho, Southern Oregon and Northern California — there is no strong signal to what the winter will be like. The southern half of the U.S., including most of California, is more likely to have a relatively warm and dry winter, according to NOAA.
La Nina has strengthened over the last two months. Between September and November, the average sea-surface temperature along the equator between Ecuador and the international dateline was 0.7 degrees Celsius below normal. That’s the same average temperature as last year for the three-month period. Washington’s snowpack was 121 percent of normal by the end of the winter, according to the USDA’s Natural Resources Conservation Service.
La Nina conditions prevail when sea-surface temperatures are at least 0.5 degrees Celsius below average. NOAA assesses the chances of La Nina sticking around through the winter at 80 percent.
NOAA reported that sea temperatures should be normal, or neutral, by sometime in the spring and remain that way through the summer.
El Nino conditions prevail when sea temperatures are warmer than average. Washington’s snowpack drought during the winter of 2014-15 occurred during an El Nino.
Elsewhere in the U.S., the three-month outlook favors below-average temperatures in the Northern Great Plains, Upper Mississippi Valley, Great Lakes, southeast Alaska and Alaska Panhandle.
Conditions favor above-normal temperatures in the southern half of the U.S., according to NOAA.