(Bloomberg) -- U.S. natural gas futures plunged, making the fuel the worst performer among major commodities, as milder autumn forecasts stoked concern that a warm winter will crush heating demand.

Gas for December delivery slid as much as 7.1% to $2.784 per million British thermal units, the lowest in almost a month.

The U.S. is poised to see mild conditions with only a few cool shots through the end of the month, according to the Commodity Weather Group. The number of heating degree days, a measure of weather-driven gas demand factoring in population, is seen at 275, which compares to a 10-year average of 316, the commercial forecaster said in a report.

Gas surged to a two-year high last month, buoyed by speculation that supplies would be tight this winter after tumbling oil prices prompted drillers to rein in gas output from crude-rich basins. Exports of U.S. liquefied natural gas have soared to a record, further eroding stockpiles. But traders often see autumn forecasts as a harbinger of winter gas demand, and unless frigid weather materializes soon, prices could struggle to stay above $3.

“The market action in natural gas reminds me that I should not trust long term weather forecast,” Phil Flynn, senior market analyst at Price Futures Group, said in a note. “The fundamentals on natural gas look supportive but if we get another warm winter, natural gas may just stay about where it is.”

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