The entire United States has a 50% or higher chance of a warmer than average winter this year. This is according to 3-month forecasts released today by the Climate Prediction Center (CPC) at the National Oceanic and Atmospheric Administration (NOAA).
“The greatest likelihoods for warmer than normal conditions are at Alaska and Hawaii,” Mike Halpert, CPC deputy director, said at a 17 October press conference. The winter outlook shows “more modest probabilities for above-average temperatures spanning large parts of the remaining lower 48 [states], from the West, across the South, and up the Eastern Seaboard.”
The center’s models for November, December, and January also weakly favor wetter than normal weather for Alaska, Hawaii, and states between the Rocky Mountains and the Mississippi Valley and dryer than normal conditions on the central West Coast and central Gulf Coast.
“Like last year, no part of the U.S. is favored to have below average temperatures this winter,” he said.
The CPC’s seasonal outlooks also forecast a shift in which regions of the country may see drought this winter.
“After a very wet spring resulted in widespread flooding in some areas, drought has reemerged in the Southeast, Southwest, and Texas thanks to a very dry and warm late summer and early fall” in a rapid-onset flash drought, Halpert said.
“Drought is expected to improve in portions of the Southeast, Mid-Atlantic, Alaska, and Hawaii, while persisting in central Texas and the Southwest [and in Puerto Rico],” he said. “Drought development is likely to occur in parts of central California.”
Neutral El Niño Means More Variability
“This is not one of our most confident forecasts,” Halpert said. “Only over Alaska and in Hawaii does the probability reach 50% for any point.”
Part of the reason for the lower probabilities is that the El Niño–Southern Oscillation (ENSO) “is most likely to be in its neutral state in the winter, meaning that neither El Niño or La Niña is expected to develop,” Halpert said.
Strong ENSO conditions, whether trending toward the warm or cold phase in the cycle, typically overwhelm long-term trends, which “favor above-average temperatures across most of the South, along the East Coast, and in Alaska and Hawaii,” he said.
Shorter-term patterns like the Arctic Oscillation and the Madden-Julien Oscillation may also play a larger role. In this winter’s ENSO-neutral state, “any forcing this year from the tropics is likely to provide impacts on subseasonal timescales, potentially resulting in more variable conditions during the upcoming winter,” he said. These 2- to 4-week patterns are difficult to forecast far in advance and were not included in the winter outlook.
The higher confidence in the Alaska and Hawaii outlooks is likely because of strongly warmer than normal (by 1°C–3.5°C) sea surface temperatures in those two regions, the team said. In Alaska, this warming has resulted in strong long-term trends in declining sea ice coverage and ice thickness and progressively later freeze dates, the forecasters said.
“The winter outlook is probabilistic in nature,” Halpert cautioned. “Less likely outcomes will and must occur from time to time. That was certainly the case last winter, when a flip in the pattern during late January brought a very cold February to parts of the North and West,” as well as other regions that were also forecasted to be warmer than normal.
—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer