BOSTON — Snow falling over Siberia is raising the prospect for frigid temperatures in New York come January.
The weather half a world from Central Park can set off atmospheric events that result in icy air descending from the North Pole in December and January, driving U.S. temperatures down and natural gas and heating oil use up, according to Judah Cohen, director of seasonal forecasting at Atmosphere & Environmental Research in Lexington, Mass.
“It’s the best winter predictor that we have,” Cohen said in a telephone interview. “We haven’t made a forecast yet, but we’re watching it closely and the snow cover has definitely been above normal so far.”
The more ground covered by snow across northern Europe and Asia at the end of October, the greater the chances of triggering a phenomenon known as the negative phase of the Arctic Oscillation. That would flood North America, Europe and East Asia with polar air and possibly erect a blocking effect in the North Atlantic that would bottle up the cold in the U.S.
In September, 2.36 million square kilometers (911,000 square miles) of northern Europe and Asia were covered by snow, according to the Rutgers University Global Snow Lab. That compared with the 1981-2010 mean of 1.5 million.
“It’s running well above normal,” said Matt Rogers, president of Commodity Weather Group, a commercial forecaster in Bethesda, Md. “Through the last week of September, it’s the highest snow total in Eurasia since 1977.”
For Rogers, snow cover isn’t as good a predictor for the U.S. winter as Cohen suggests.
“It works about 60 to 70 percent of the time,” Rogers said. “I use it as a factor in our seasonal outlook.”
The winters of 2009-2010 and 2010-2011 are examples of what can happen when the Arctic Oscillation shifts into its negative phase. A total of 51.4 inches of snow fell in Central Park in 2009-2010 and 61.9 inches in 2010-2011, for the two snowiest years of the century so far, according to National Weather Service records. Eurasian snow totaled 11.55 million square kilometers in October 2009 and 10.81 million a year later, both above the mean of 9.49 million, Rutgers data show.
During the winter of 2011-2012, when there wasn’t as much of an impact from the Arctic Oscillation, 7.4 inches fell in New York, the sixth-lowest level on record. The snowfall in Siberia in October 2011 measured 9.47 million square kilometers.
“The negative phase of the Arctic Oscillation is a big huge indicator of a huge area of cold air coming down,” said Paul Pastelok, a meteorologist at AccuWeather Inc. in State College, Pa.
November is the start of the five-month heating season, when gas heating demand peaks. December accounts for 20.9 percent of the winter fuel use while February takes 22.6 percent and January tops the heap with 25 percent.
Gas inventories will end the heating season at about 1.72 trillion cubic feet, the Energy Information Administration, the Energy Department’s statistical arm, estimates. A major cold outbreak might push that down to 1.54 trillion, while a warmer- than-normal winter could bring in inventories closer to 1.89 trillion, said Teri Viswanath, director of commodities strategy at BNP Paribas in New York.
“It shows you the range and how important a significant cold break out can be,” Viswanath said. “It will have an impact on the range of inventory levels that will have a significant impact on price.”
The EIA predicts heating oil prices will average 5 percent lower this winter, while natural gas prices will rise slightly. There is a 35 percent chance gas prices will be $4 per million Btu and an 11 percent chance they will be greater than $4.50, according to the agency.
“The industry hasn’t factored a cold event into the market right now,” Viswanath said.
A strong snap of frigid air in the central U.S. this January and February might push prices up by 75 cents, she said.
As in most forecasting, the snow in Eurasia is just one factor to be considered for predicting winter, Rogers said. In his official outlook, Rogers said he expects cold early in the season with the second half of the winter milder.
One pattern that can negate Siberian snow is an oscillation in the stratospheric circulation of winds, said Robert Allen, an assistant professor of climatology at the University of California at Riverside.
If they don’t line up right, the snow loses its ability to trigger sweeping cold events in the temperate regions, said Allen, who co-wrote a paper on the subject in 2011.
The increase in Eurasian snow may be a side-effect of climate change, Allen said. The Arctic ice cap shrank to a record low last year, according to the National Snow & Ice Data Center, and always reaches its smallest in September. The added moisture in the air might fuel snowstorms, he said.
Todd Crawford, chief meteorologist at WSI Corp. in Andover, Mass., said the amount of snow falling across Eurasia has been slowing and winds might not be setting up to allow cold blast to occur.
Cohen said the entire month of October is important in making the seasonal forecast, which his group issues next month. Whether he predicts a mild winter or a frigid one, Cohen said he will be looking at the snow in Eurasia for clues.