Natural-gas futures broke an important area of resistance Wednesday as forecasts of slightly lower gas inventories and an exceptionally early cold front in the Midwest drove up prices.

The run-up came as analysts predicted the U.S. government would report a smaller increase in natural-gas inventories compared with the week-earlier figure, though the overall market still suffers from a production glut.

Additionally, temperatures are expected to drop further in the Midwest, prompting some consumers to fire up their furnaces earlier than usual. The impact on demand, though small, could signal a colder winter over the next few months, a trend that would give gas prices added support.

Natural gas for September delivery settled up 5.9 cents, or 1.5%, at $4.039 a million British thermal units on the New York Mercantile Exchange. The benchmark contract traded between $3.955/mmBtu and $4.099/mmBtu.

The Energy Information Administration is likely to report that 80 billion cubic feet of gas were added to storage during the week ended Sept. 9, according to the average prediction of 16 gas analysts and traders in a Dow Jones Newswires survey.

That injection would be smaller than the week-earlier increase but slightly above the five-year average.

Research firm Ritterbush and Associates noted the market crossed a significant level of resistance late in the afternoon at $4.04/mmBtu, the highest level since the start of the month.

Citigroup analyst Tim Evans said many bearish traders are likely covering their short positions ahead of the EIA report.

At the same time, small deviations from average weather patterns tend to have an outsized effect on futures prices as traders look for small cues that could signal changes in potential demand.

"We're less worried about how quickly storage is rising and starting to focus on the approaching winter," Evans said, though "in absolute terms, it's still not that cold in the north and it's not going to be that hot in the south."