After four solid weeks of steep increases, natural gas forward prices buckled during the trading period ending Tuesday as the start of the fall season ushered in cooler weather and a decline in demand. October prices plunged an average of 54.0 cents from Sept. 16-21, while November tumbled 55.0 cents on average, according to NGI’s Forward Look.

The hefty price discounts extended through the winter strip as the milder weather outlook was seen leading to a string of much larger storage injections than the ones that amassed over the summer. The November 2021-March 2022 strip came off an average 52.0 cents for the period, Forward Look data showed. Summer prices also were lower by an average of 13.0 cents.

Given the quick and steep climb the Nymex futures strip experienced over the...