  We analyzed data for the Electric Reliability Council of Texas (ERCOT) to
assess shoulder seasons -- that is, the 45 days of lowest total energy use and
peak demand in the spring and fall typically used for power plant maintenance
-- and whether their occurrence has changed over time. Over the period
1996--2022, the shoulder seasons never started earlier than late March nor
later than mid-October, corresponding well with the minimum of total degree
days. In the temperature record 1959--2022, the minimum in degree days in the
spring moved earlier, from early March to early February, and in the fall moved
later, from early to mid-November. Warming temperatures might cause these
minima in degree days to merge into a single annual minimum in December or
January by the mid-2040s, a time when there is a non-trivial risk of 1-day
record energy use and peak demand from winter storms.
