WEATHER

What a winter shift to the queen of climate patterns means for Florida

Kimberly Miller
Palm Beach Post

Much of Central and South Florida are edging toward a winter drought with an entrenched repeat La Niña and double-digit rainfall deficits along the southeast coast, according to a federal forecast issued Thursday.

No drought is expected in the Panhandle, but the arcane La Niña does suggest hotter and drier days statewide for December through February.

While it’s not completely understood why the climate pattern occurs in consecutive winters – last winter’s La Niña called it quits in April – the influences are the same.  

The Climate Prediction Center’s winter outlook for Florida points to an up to 70% chance of warmer than normal temperatures for the coldest season of the year and an up to 50% chance of below normal rainfall.  

NOAA's Climate Prediction Center's drought outlook for winter 2021.

For areas from Orlando through Miami that means a “tendency” for drought to develop – chances that are exacerbated by year-to-date rainfall rates that through Wednesday are 12 inches below normal for coastal Palm Beach County as measured by the South Florida Water Management District.

Eastern Miami-Dade county’s rainfall this year is 10 inches below normal with the southwest coast experiencing a 6-inch deficit. Martin and St. Lucie counties were 7.3 inches below normal as of Wednesday.

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What La Niña means for temperature and rainfall in the winter months

Jon Gottschalck, chief of the Climate Prediction Center’s Operational Prediction Branch, said La Niña climate patterns typically have stronger ties to rainfall rates than temperature. This La Niña, which was declared earlier this month, is not as strongly coupled to precipitation because of more divergent forecast models, Gottshalck said.

090211   (Lannis Waters/The Palm Beach Post) WEST PALM BEACH -   Markers showing the low water level for the drought years of  2007, 2001, and 2009 sit in the water at Clear Lake Friday morning September 2, showing a very different shoreline than shown in a photo taken June 9, 2011.

“For temperature, we have a higher confidence where our probabilities are greater than 50% for much of the southeast and Gulf Coast, including Florida,” he said.

The climate patterns El Niño and La Niña are part of the powerful El Niño-Southern Oscillation, or ENSO. 

During El Niño, warm water that has been pushed by trade winds into the western reaches of the Pacific Ocean rushes back east. That movement shifts where deep tropical thunderstorms form. The exploding storms, whose cloud tops can touch the jet stream, disrupt upper air flows. In summer, El Niño creates wind shear that chops up Atlantic tropical cyclones. In winter, El Niño nudges the jet stream south giving Florida cooler, wetter winters.

NOAA's Climate Prediction Center's precipitation outlook for winter 2021.

La Niña happens when Pacific waters cool, moving the tropical thunderstorms so that the wind shear in the Atlantic wanes during hurricane season. In winter, La Niña pulses storms into the Pacific Northwest on a more northerly and inland track, holding the jet stream at higher latitudes longer where it traps cold air to its north.

But there’s no guarantee with either pattern.

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“It’s not a slam dunk that every time we have a La Niña that we’ll have the climate pattern of warm and dry,” said Florida Climatologist David Zierden.

2010 was last time winter was cooler than normal in South Florida

For example, the last winter that was cooler than normal for South Florida was 2010, which included a 12-day period between Jan. 2-13 that was the coldest on record since at least 1940. But 2010-2012 also included multi-year La Niña patterns.

The December 2020 through Feb. 2021 period capped a decade of warmer than normal winters for South Florida, but La Niña had competition that made it a close call. 

NOAA's Climate Prediction Center's temperature outlook for winter 2021.

Through January, a series of cold fronts dug deep into Florida as a swirl of high pressure in Canada amplified kinks in the jet stream – shooting it into the frigid north and plunging it south into the sultry tropics. The repeat volleys of chill included an unusual South Florida frost that settled on areas from the Glades to Palm Beach. The temperature at Palm Beach International Airport dipped to 39 degrees on Feb. 4, which is 19 degrees below normal.

It wasn’t until later in February that an unusual warmth gripped the Sunshine State as high pressure over the western Atlantic Ocean acted like a forcefield against intrusions of cold air.

West Palm Beach ended the winter about 2 degrees above normal and 4 inches below average in rainfall.

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Last winter also had spats of unusually wet periods in the Panhandle with the National Weather Service in Tallahassee reporting 6.81 inches of rain in January – about 2.5 inches above normal. January also whipped up two EF-1 tornadoes near Tallahassee – something atypical for La Niña.

“But that doesn’t mean this go around we won’t see that traditional warm and dry winter,” said Zierden, who noted climate change as an underlying contributor to the warmer temperatures. "Just across the southeast we have had a very significant warming trend and without a doubt that's linked to climate change."

The sun rises over Palm Beach in 2020.

How big a concern will Florida wildfires be this winter?

Wildfires have also been a concern in Florida during previous La Niña events, but there is less of a correlation since about 2000 when the state increased the use of prescribed burns, Zierden said.

Nationwide, the Climate Prediction Center is forecasting below normal temperatures for a slim swath of states including Oregon, Washington, northern Idaho, Montana and western to central North and South Dakota. The majority of the contiguous U.S. is predicted to see varying probabilities of warmer than normal temperatures, from Central California through Maine.

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Above normal rainfall is forecast for the northwest, Great Lakes and a slice of states from Missouri through New York.

“The correlation with La Niña isn’t 100%,” said AccuWeather senior meteorologist Dale Mohler. “There aren’t too many relationships in weather that are 100%, but it’s still a pretty solid one.”

Double-dip La Niña patterns are normal but not well understood. It’s “uncommon” for there to be a repeat El Niño, according to a NOAA climate article.  

Mohler said, in general, El Niño patterns get strong and then quickly snap back to neutral with more extreme temperature changes.

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La Niña tends to be weaker, leaving a cool signal behind even when the pattern shifts to neutral. When fall comes, it’s easier for the lingering cooler water to deepen and reenter another La Niña phase.

“There’s no simple answer,” Mohler said. “But I would say four out of five La Niña patterns are double dip.”

Kimberly Miller is a veteran journalist for The Palm Beach Post, part of the USA Today Network of Florida. She covers weather, climate and the environment and has a certificate in Weather Forecasting from Penn State.  Contact Kim at kmiller@pbpost.com