Silicon Valley enjoys a mild Mediterranean climate: warm dry summers, cool wet winters, and relatively few extreme-temperature days compared with the rest of the country. Below: live conditions, the 7-day outlook, and what it means for electricity demand on the CAISO grid.
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High and low temperatures, with the implied heating and cooling demand below.
Mild weather keeps raw degree days low, but California's challenge is timing, not totals. As rooftop and utility solar fade at sunset, demand and net load ramp hard into the evening just as cooling needs linger on a warm day. Heat waves across the wider CAISO footprint, plus wildfire-season public-safety power shutoffs, are the real grid stressors here, more than local temperature alone.
CAISO's tightest hours are the early-evening ramp (roughly 5 to 9 pm) on warm days, when solar drops off and air conditioning is still running.
See live CAISO grid data →They measure how far the day's average temperature sits from a comfortable 65°F. Cooling degree days (CDD) count degrees above 65 and track air-conditioning demand; heating degree days (HDD) count degrees below 65 and track heating demand. More degree days means more energy used to keep buildings comfortable, and a higher grid load.
Temperature is the single biggest short-term driver of electricity demand. Hot afternoons and cold mornings push load toward the grid's limits, which is when prices rise and reliability is tested. Watching the forecast is watching the grid's next few days.
Live weather and the 7-day forecast come from Open-Meteo. Degree days are computed from the forecast highs and lows against a 65°F base. Live grid data is on the CAISO region page.