Natural gas futures tumbled lower in early trading Monday, crashing through the $4/MMBtu barrier as weekend forecast trends further reduced already-mild weather-driven demand expectations. The January Nymex contract was down 38.4 cents to $3.748/MMBtu at around 8:50 a.m. ET.

NGI Morning Natural Gas Price & Markets Coverage

Both the American and European modeling agreed on forecast trends over the weekend that would cut an additional 20 gas-weighted degree days over the 15-day projection period, according to Bespoke Weather Services.

The latest warmer shift added to a temperature outlook that was already poised to make this December one of the mildest on record, the firm said.

The forecast as of early Monday “now has us solidly on track for the second warmest December on record, behind only December 2015, which will be...