Ameren Illinois warns that unpredictable weather, especially heat waves, could further drive up electricity costs. Last year, a heat wave with ten consecutive days of triple-digit temperatures led to unexpectedly high bills. Increased air conditioning use during extreme heat strains the power grid and increases prices. Despite these potential price spikes, MISO reports a reserve capacity of 11.4% for the summer, much higher than New York's 1.2% margin, suggesting a stable electricity supply for central and southern Illinois.