Natural gas exchange traded funds took a sharp turn Wednesday after rallying on a shift in the weather outlook. Traders who are wary of further weakness in the gas market may want to keep inverse or bearish fund options close at hand.

On Wednesday, the United States Natural Gas Fund (NYSEArca: UNG) fell 4.8%% and the iPath Bloomberg Natural Gas Subindex Total Return ETN (NYSEArca: GAZ) declined 11.9%. Over the past week, UNG jumped 18.4% and GAZ surged 17.4%.

Nymex natural gas futures decreased 7.1% Wednesday to $2.20 per million British thermal units.

Meanwhile, inverse natural gas ETFs that capitalize off weakness in the commodity surged. For instance, the VelocityShares Daily 3x Inverse Natural Gas ETN (NYSEArca: DGAZ) seeks to provide the daily inverse 3x, or -300%, performance of the NYMEX natural gas futures. The ProShares UltraShort Bloomberg Natural Gas (NYSEArca: KOLD) provides the daily inverse 2x, or -200%, performance. On Wednesday, DGAZ increased 12.4% and KOLD advanced 8.0%. [Why Natural Gas ETFs May Get Burned]

Natural gas dipped for for the first time in five days on a milder weather outlook next month, which could diminish natgas heating demand and leave the ongoing supply glut unchecked, reports Naureen Malik for Bloomberg.

According to the Commodity Weather Group LLC, temperatures across the Midwest and East Coast will be above normal January 4 through January 8 and could continue to linger the following week.

“Going forward we are going to be vulnerable to weather, and unless we see really sustained periods of cold weather, the market is going to have trouble rallying,” Gene McGillian, senior analyst at Tradition Energy, told Bloomberg. “This last week had a 70-cent run and the magnitude was probably exaggerated by how far we had dropped in the first couple of weeks of December.”

The ongoing El Nino weather phenomenon, which occurs when the Pacific ocean surface temperatures rises, has helped fuel an uncharacteristically warm winter across the continental U.S. Weather forecasters are also anticipating a stronger-than-expected El Nino that could last through early 2016.