Natural gas soared the most in nine years as forecasts for lingering U.S. cold spurred concern that supplies may not be adequate to meet demand over the winter.

Gas for December delivery rose as much as 20 per cent to US$4.929 per million British thermal units, the highest since February 2014, when a “polar vortex” brought an arctic chill to the Midwest and East. The volume of trading on the New York Mercantile Exchange was about three times the 100-day average.

The premium for March 2019 gas over the April contract jumped to US$1.745, the widest in data going back to 2015. The March-April spread, dubbed the “widowmaker” for its volatility, is an indicator of how well supplied traders expect the market to be during the winter.

Prices have been driven by “a sharp cold revision in the winter weather outlook,” said Devin McDermott, a commodities strategist at Morgan Stanley. “We see modest downside from here assuming current weather forecasts, but a very wide range of potential short-term prices.”

It was only on Tuesday that that gas exceeded the US$4 mark for the first time in four years. The fuel surged this month amid concern that stockpiles, at a 15-year seasonal low, won’t be enough to help meet winter heating needs, even as production hovers near a record. In North America, gas stowed in underground aquifers and salt caverns in summer months is used to supplement supplies pumped from wells during winter.

Domestic and foreign demand for American gas has climbed to all-time highs. Cheniere Energy Inc. said Wednesday it started producing liquefied natural gas at its new US$15 billion Corpus Christi export terminal in Texas, the third such plant to begin operating in the continental U.S.

Gas is also climbing amid turmoil in international crude markets, where U.S. benchmark prices advanced Wednesday after tumbling 7.1 per cent a day earlier.

Despite the autumn chill, the magnitude of the latest rally suggests traders aren’t just reacting to weather forecasts and supply estimates, according to Mizuho Securities USA LLC. While money managers are net-long in gas contracts, short positions rose as recently as last week, government data show.

Wednesday’s jump “has no basis in market fundamentals,” said Bob Yawger, director of the futures division at Mizuho. “It is getting cold, it might snow” and storage is lower than normal, “but that is not why we are 12 per cent to 15 per cent higher on the day.”

Futures were up 11 per cent at US$4.54 at 11:33 a.m. The gas price jump triggered an expansion in the daily trading limit to US60 cents from US30 cents for a second straight day. Spot gas prices rose Tuesday. In Portland, the price climbed 78 per cent to US$10.78, the highest since late January. The ProShares UltraShort Bloomberg Natural Gas ETF fell as much as 26 per cent Wednesday, the most since 2012, while VelocityShares Daily 3x Long Natural Gas ETN soared as much as 37 per cent, also the most in six years. Cold conditions are stoking concern that U.S. production may be interrupted due to the freezing of well heads. “We may be seeing the first freeze-offs of the winter,” market data and analysis company Genscape Inc. said in a report Wednesday. Forecasts for Nov. 24-28 have turned colder for parts of the southern and eastern U.S, according to the Weather Company. Read More: The natural gas  rally will probably keep prices supported above US$3.80 this winter, Morningstar Inc. says. Gas volatility has soared to the highest since February as futures climb. Frigid weather may be  choking off gas supplies at a time when the market is most vulnerable to price spikes.