Natural gas prices have surged, with related ETFs testing their long-term trendline, as a cold snap bears down on the U.S.

The United States Natural Gas Fund (NYSEArca: UNG) rose 2.9% Thursday and was testing its long-term, 200-day simple moving average as Nymex natural gas futures hovered around $3.5 per million British thermal units. UNG is up 10.3% year-to-date and surged 22.5% over the past month.

Natural gas prices have jumped to their highest level in more than a year, with prices surging over 6.8% on Tuesday alone, as cold arctic air is expected to cover the U.S.

Further fueling the rally in natural gas prices, short traders are being squeezed and forced to buy back contracts they sold to close out their positions, reports Alison Sider for the Wall Street Journal.

Weather forecasts project warm temperatures in the latter part of January will quickly give way to a wave of bitter cold from the Midwest down to Texas and eastward as a high-pressure ridge over Alaska sets course to blow arctic air down through North America.

“The market was antsy, waiting for that first clear sign of cold. [Tuesday] it arrived,” Jacob Meisel, chief weather analyst at Bespoke Weather Services, told the WSJ.

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