Fueled by unrelenting heat across Pacific Northwest, Western Canada and the East Coast, natural gas forwards surged in the trading period ending June 30, according to NGI’s Forward Look.

August prices shot up an average 19.0 cents over the six-day period, led by an astounding C28.0-cent climb at NOVA/AECO C. The stout gains continued throughout the front of the curve and extended through next winter, as the likelihood increased that storage inventories would be much less than normal ahead of the peak demand season.

The oppressive heat led to numerous fatalities. The death toll was in the dozens as of Thursday, with at least 13 deaths in the Seattle area being attributed to the excessive hot weather. In Oregon, the medical examiner’s office in Multnomah County, which...