NOAA’s long-term forecasts for the 2018-19 winter don’t herald favorable conditions for skiers and snowboarders in Sun Valley, but there’s no reason to panic just yet.
NOAA’s forecasts offer wide-ranging predictions of above-normal or below-normal temperatures and precipitation patterns for the U.S. The forecasts are probabilistic.
The amount of snow and the ski conditions on Bald and Dollar mountains in November, December, January, February and March will depend on week-to-week changes in temperature as well as storm tracks that blow in off the Pacific Ocean, which the long-range forecasts cannot account for.
Still, NOAA issued its forecasts last week and predicted warmer-than-normal temperatures for central Idaho as well as drier-than-normal conditions for December through February.
For Ketchum, the National Weather Service predicts a 49 percent chance of a warmer-than-normal winter, a 32 percent chance that temperatures will be near normal and a 19 percent chance that temperatures will be below normal.
A weak El Niño is expected to form in the Pacific Ocean this winter. NOAA forecasts call for a 70 to 75 percent chance of that occurring.
A weak El Niño was present in the winter of 2014-15, which resulted in good early-season snowfall in the Wood River Valley. Warmer temperatures that accompanied February storms created heavy rainfall and slushy conditions in Ketchum.
“We expect El Niño to be in place in late fall to early winter,” said Mike Halpert, deputy director of NOAA’s Climate Prediction Center, in a news release. “Although a weak El Niño is expected, it may still influence the winter season by bringing wetter conditions across the southern United States and warmer, drier conditions to parts of the North.”
That will be a shift from the previous two winters, when La Niña conditions were present. The winter of 2015-16 featured a historically strong El Niño in the Pacific Ocean and brought bountiful snowfall to Sun Valley in December and January.
The winter of 2016-17 featured La Niña conditions and resulted in a record-setting snowpack in the mountains above the Wood River Valley. Those conditions were again present last winter, but the snowfall was slow to come. The first big snowstorm did not reach Baldy until mid-January, and major snow arrived in late February and early March.
What’s the difference between the two climatic events? El Niño refers to “a warming of the ocean surface, or above-average sea surface temperatures in the central and eastern tropical Pacific Ocean,” according to a definition from NOAA.
La Niña represents “a cooling of the ocean surface, or below-average sea surface temperatures in the central and eastern tropical Pacific Ocean.”
Coupled with oceanic water temperatures farther to the north, those conditions influence the tracks that storms take as they reach the Western U.S.
Another condition that was a factor in the winter of 2014-15 was a so-called “Blob” of warm water that formed in the Gulf of Alaska. That has returned this fall: Water in the northeast Pacific Ocean, off the coast of Alaska, was extremely warm in September and early October, according to NOAA.
The Blob started to form in late 2013, according to a 2016 report from the NOAA Fisheries Ecology Division.
“The heat wave emerged in the fall of 2013, when a ridge of high pressure dampened winds over the Gulf of Alaska, allowing a large section of the North Pacific to warm by up to 3 degrees (Celsius) above average,” according to the report. “It represented the highest temperature anomaly in the North Pacific in more than 100 years of records.”
A high-pressure system set up over Alaska in late September, delivering record-breaking high temperatures to the state this fall.
“The North Pacific Ocean is warm—really warm—at least compared to normal,” wrote Rick Thoman of the Alaska Center for Climate Assessment and Policy, on the NOAA website on Oct. 15. “September temperatures in Alaska tied for fourth warmest in the past 94 years.”
It’s unclear if that will linger in the months to come, but it could be another factor in influencing the West Coast’s winter storm track, according to NOAA. It may have contributed to earlier October snowfall in parts of the mountain West.