‘No Nino’ leaves forecasters guessing about winter | PostIndependent.com

‘No Nino’ leaves forecasters guessing about winter

Heather McGregor
Post Independent Editor
Glenwood Springs, CO Colorado
Heather McGregor Post Independent illustrationNovember marks the beginning of the winter snow season, and the 2012-13 season is starting out very dry. This chart shows the water content in the snowpack at sites high in the Crystal, Roaring Fork, Fryingpan and Deep Creek basins, compared to where the water content would be on Nov. 30 of an average year. Source: U.S. Natural Resources Conservation Service.

GLENWOOD SPRINGS, Colorado – Visibility is limited on the outlook for this winter’s weather, says state climatologist Nolan Doesken.

The weather patterns of this year and the two preceding years have only been seen once before in recorded weather data, in the 1950s. And the outcome that time was a prolonged drought lasting for three years, Doesken said.

But one set of precedent years doesn’t make for a secure prediction now, Doesken said.

“Do we know what this winter is going to do? No,” said Doesken on a visit to Glenwood Springs earlier this week.

Snow survey reports from Friday show that statewide and throughout the inland Western states, a severe drought persists and the winter snowpack is starting out well below average.

Snowpack in the Colorado River watershed, from Grand Junction to the Continental Divide, is at 41 percent of average for Nov. 30, according to data on the U.S. Natural Resources Conservation Service website.

In the state’s eight major river basins, snowpack ranges from a low of 27 percent in the Arkansas to 52 percent in the Platte.

Reservoir storage is also below normal for late fall, at the end of a year that has already been extremely dry.

Ruedi Reservoir on the Fryingpan River is 44 feet below its high water mark and holding 63 percent of capacity, said Kara Lamb, spokeswoman for the U.S. Bureau of Reclamation.

Green Mountain Reservoir on the Blue River is 53 feet below its high water mark and holding just 44 percent of capacity, she said.

At both reservoirs, releases are greater than the estimated inflow, so reservoir levels continue to inch downward.

“The reservoirs were drawn down over the summer, but in November we usually start to see the inflow and outflow balance, so we can start storing. But this year, that hasn’t happened yet. The outflow is still greater than inflow,” Lamb said.

“It’s hard to speculate on the weather,” she said. “It would sure be nice to have some snow come through.”

At present, however, temperatures in the Pacific Ocean are giving forecasters little to no indication of what’s ahead.

The National Oceanic and Atmospheric Administration’s current three-month forecast is for temperatures above normal in southwest Colorado and at normal in a swath stretching from northwest to southeast Colorado, including Garfield County.

NOAA’s precipitation forecast is more neutral, calling for equal chances of above normal, normal or below normal precipitation from December through February.

Doesken explained that the forecasts are in part based on the El Nino Southern Oscillation, which is a sloshing of warmer and cooler ocean waters sliding from east to west in the Southern Hemisphere, between Southeast Asia and South America.

In El Nino years, the warmer Pacific water sloshes up against the coast of South America. In La Nina years, which prevailed in the winters of 2010-11 and 2011-12, the warmer water pools up in the eastern Pacific.

El Nino years tend to bring wet storms into southern California and across the southern U.S., blessing southern Colorado with a hefty snowpack. La Nina years send the weather farther north, with more storms moving from the Pacific Northwest and across the northern states and Canada, dropping more snow in northern Colorado, Doesken said.

Starting last spring, it appeared the Southern Oscillation would shift to El Nino, and by July, rain began to fall in the West. The shift became more pronounced in August, but by September the oscillation reversed, he said. Now the situation is seen as neutral, which the National Weather Service has dubbed “No Nino.”

“All the computer models predict it to remain neutral for the next six to eight months,” Doesken said. “Historically, neutral hasn’t been bad for Colorado. Quite a few neutral years have had decent, snowy winters.”

But in the one known example of two La Nina years followed by a “No Nino,” huge snowfall occurred in December 1951, but 1953 through 1956 were very dry years.

“There are lots of uncertainties,” Doesken said. “We don’t know for sure, but there is a nagging concern with the storm track missing southern California and not delivering much of anything to Colorado. We could be looking at a second dry year for northern Colorado, and a third dry year for southern Colorado.”

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