[DavidPeiffer]

Those are general demand curves, and are not necessarily representative of the coolest days of the season. What we care about is the gap between supply and demand.

From experience buying large industrial quantities of natural gas, the larger market can see bad effects at low temperatures. Even in the upper Midwest you can get force majeure events, particularly when temperatures drop below 0 F for a couple days.

The winter months bring planned shutdowns for power plants to perform maintenance, trying to prevent downtime during the summer heat. The non-linear nature is a concern, though in cases almost up to the 1:1 point, it's more energy efficient to burn natural gas to create electricity and use a heat pump compared to burning natural gas in the home.