Ushering in the official start to the fall season, weekly natural gas cash prices gave up substantial ground amid mild temperatures, fading cooling demand and rising production. NGI’s Weekly Spot Gas National Avg. for the Sept. 19-23 trading period fell $1.185 to $6.485.

Heat early in the week quickly dissipated by midweek and, as the official start to autumn arrived Thursday, comfortable conditions permeated much of the Lower 48, from the West Coast to the Midwest to the East.

When cash market trading culminated for the week, SoCal Citygate was down $1.765 to $6.965, while Chicago Citygate was off $1.180 to $6.425 and Algonquin Citygate near Boston was down $1.415 to $6.150.

The October Nymex futures contract also faltered through the course of the past week as bearish...