Summit County Citizens Voice

An active northern jet stream has helped deliver good early season snows to Colorado.

NOAA releases 90-day outlook; La Niña impacts expected to persist into spring

By Bob Berwyn

SUMMIT COUNTY — This year’s La Niña weather, with cooler-than-average water temperatures in the eastern equatorial Pacific, is still being rated as moderate to strong in the latest 90-day outlook issued by the National Weather Service this week. The La Niña pattern is expected to persist at least through January, and possibly well into spring.

“It’s too big to fade,” said Klaus Wolter, a National Oceanic and Atmospheric Administration climate researcher who has helped develop medium and long-range forecasts based on factors like the La Niña-El Niño cycles. Wolter said some of this year’s La Niña impacts are typical, including above-normal precipitation in the Pacific Northwest and the northern Rockies.

The National Climate Prediction Center explained that water temperatures are below normal along the full lengths of the Pacific Coasts of both North and South America. The coolness extends up to 600-feet deep into the water, making it likely La Niña will persist well into spring. Here’s an excerpt from the NOAA climate prediction website:

MODERATE TO STRONG LA NINA CONDITIONS CONTINUE IN THE TROPICAL PACIFIC OCEAN.
SEA SURFACE TEMPERATURES (SSTS) IN THE EQUATORIAL PACIFIC OCEAN ARE BELOW AVERAGE FROM AROUND 160E TO THE SOUTH AMERICAN COAST, WITH SSTS BETWEEN 1 AND 3 DEGREES C BELOW NORMAL IN MOST AREAS.  SSTS ARE BELOW NORMAL IN THE EASTERN PACIFIC OCEAN BETWEEN 20N AND 20S WITH BELOW NORMAL COASTAL SSTS EXTENDING JUST ABOUT THE FULL LENGTH OF THE PACIFIC COASTS OF NORTH AND SOUTH AMERICA.  THIS VERY LARGE AREA OF ANOMALOUSLY COOL SSTS HAS SIGNIFICANT IMPACT ON THE LARGE SCALE ATMOSPHERIC CIRCULATION THROUGHOUT THE TROPICAL PACIFIC REGION, WHICH, IN TURN, IS EXPECTED TO CONSIDERABLY INFLUENCE THE MEAN ATMOSPHERIC CIRCULATION PATTERNS OVER NORTH AMERICA.  SUB-SURFACE OCEAN TEMPERATURES ARE ALSO WELL BELOW AVERAGE IN THE EQUATORIAL EASTERN PACIFIC TO OVER 200 METERS DEPTH, STRONGLY FAVORING A CONTINUATION OF LA NINA CONDITIONS INTO AT LEAST THE SPRING OF 2011. FORECASTS FROM MOST SST PREDICTION MODELS SUPPORT THIS CONCLUSION, WITH SST ANOMALIES PREDICTED TO GRADUALLY DIMINISH INTO THE EARLY SUMMER MONTHS.

Wolter said he expects the La Niña signal to remain strong at least for the next six weeks, through the end of January.

But there have also been a few surprises that don’t fit the pattern. including another chilly winter in the Southeast extending as far south as Florida. It’s possible that the La Niña impacts are being outweighed by changes in an Atlantic pattern known as the North Atlantic Oscillation — which encompasses changes in air pressure differences between a permanent low pressure system over Iceland and a high pressure system over the Azores.

The relative position and strength of those systems guides westerly winds and helps shape the weather along the East Coast, but even more so in Europe. The second frigid winter in a row across large parts of Europe highlights the importance of the North Atlantic Oscillation. There has been some speculation among climate researchers that warming temps in the Arctic region, related to the long-term trend toward decreased sea ice, may be linked to colder weather in lower latitudes.

“There’s  a lot of discussion about that right now,” Wolter said. And while the Front Range is expected to be somewhat dry during a La Niña, this year has been one of the driest on record for parts of the region, including Boulder, which has only seen 2 inches of snow through mid-December, putting this season on track to be the driest in 117 years of record-keeping.

Wolter said one of the big factors in the Front Range weather has been the absence of any Arctic air masses moving south to help trigger precipitation. For December, that means temperatures have running 4 to 6 degrees above normal in many locations in Colorado.

Wolter also said the incoming wave of Pacific moisture is looking like a potent weather-maker for western Colorado starting this weekend.

“I wouldn’t be surprised if some locations picked up 1 to 2 inches of moisture,” he said, adding the storm is originating over some warm Pacific waters, so snow levels could be quite high as the weather moves in on a westerly flow.

Hee’s an except for the the three-month January through March period:

THE SEASONAL PRECIPITATION OUTLOOK FOR JFM 2011 FAVORS ABOVE-MEDIAN PRECIPITATION FOR PARTS OF FAR NORTHERN CALIFORNIA, THE PACIFIC NORTHWEST, THE NORTHERN ROCKY MOUNTAINS, NORTHERN GREAT PLAINS AND THE UPPER GREAT LAKES.
ABOVE MEDIAN PRECIPITATION AMOUNTS ARE ALSO FAVORED FROM THE CENTRAL MISSISSIPPI VALLEY NORTHEASTWARD TO THE LOWER GREAT LAKES AND PARTS OF NEW ENGLAND.  THE CHANCES OF BELOW-MEDIAN PRECIPITATION AMOUNTS ARE ENHANCED FROM SOUTHERN CALIFORNIA TO WESTERN TEXAS, AND ALSO IN PARTS OF THE GULF COAST AND THE SOUTHEASTERN U.S.  THIS PRECIPITATION PATTERN REFLECTS THE WEAKER THAN AVERAGE SOUTHERN UPPER LEVEL JET STREAM TOGETHER WITH AN ACTIVE NORTHERN JET THAT IS USUALLY OBSERVED IN LA NINA WINTERS.  LA NINA COMPOSITES AND CFS FORECASTS SLIGHTLY FAVOR BELOW MEDIAN PRECIPITATION ALONG ALASKA’S SOUTHERN COAST.

Visit the Climate Prediction Center online for more.

Filed under: Summit County Colorado, Summit County snow and weather Tagged: | Climate Prediction Center, Cold Europe weather 2010, Colorado snow and weather, El Niño-Southern Oscillation, LaNiña, National Oceanic and Atmospheric Administration, North Atlantic Oscillation 2010, Sea surface temperature, Summit County News, Summit County snow and weather