“A strong El Niño is in place and should exert a strong influence over our weather this winter,” said Mike Halpert, CPC’s deputy director.
Halpert said this year’s El Niño is among the three strongest on record since 1950 and may end up ranking as second strongest, only lagging the 1997-1998 event. Strong events have characteristic footprints on regional weather patterns, although they are not etched in stone: “[El Niño] provides basis for a more confident winter outlook,” Halpert said. “[But] the climate system is much more complicated than an El Niño, even a strong one.”
El Ninos, particularly when they’re strong, heavily tilt the odds for wetter than normal conditions across the southern tier of the U.S. They energize the southern branch of the jet stream, which transports moisture-laden weather systems from coast to coast.
While the NWS outlook shows a strong signal for elevated precipitation prospects in Southern California, it forecasts the highest chances for above normal precipitation from the eastern Carolinas to Florida.
Meanwhile, across the northern U.S., El Niños tend to nudge the polar branch of jet stream northward, which reduces the southward penetration of brutally cold Arctic air. It gives especially high odds for above normal temperatures in the Pacific Northwest and northern Great Lakes.
But the NWS cautioned northern residents not to let their guard down. “El Niño is not the only player,” Halpert said. “Cold-air outbreaks and snow storms will likely occur at times this winter.”
In the Washington, D.C. area, the NWS outlook shows a very slight preference for a warmer and wetter than normal winter. Historically, strong El Nino winters in the D.C. area have exhibited wildly variable snowfall. In some cases, extremely heavy snow has fallen while in others virtually none.
“We’ve seen even in warmer winters, big snowstorms in the Mid-Atlantic and Northeast,” Halpert said.
In general, the effects of El Niño across middle parts of the country are more subtle and difficult to predict compared to the north and south. Hence, the NWS says there are ‘equal chances’ for above and below normal temperatures and precipitation in this region.
The elevated chances for heavy precipitation in Southern California is welcome news in a region plagued by one of its worst droughts in recorded history. But a concern is that while past strong El Niño events have resulted in copious rain amounts, downpours have frequently come in very short periods of time leading to devastating flooding and mudslides.
The 1997-98 El Niño, the strongest on record, brought relentless storms that caused 17 deaths and over half a billion dollars in damage to California. In February alone, 13.68 inches of rain fell in downtown Los Angeles.
And even if the heavy rains come as predicted, it would likely only put a small dent in this historic drought.
California would need close to twice its normal rainfall to get out of drought and that’s unlikely,” said CPC’s Halpert.
Alan Haynes, service coordination hydrologist for the California Nevada River Forecast Center, stressed that while the forecast favors above normal rain in Southern California, precipitation is more of a wildcard in Northern California. “There’s a lot of uncertainty in our complex climate system,” Haynes said.
Additional winter outlook reading: