A persistent heat dome is bringing dangerous October heat to millions of people in the western United States, with extreme heat warnings in effect for much of coastal Southern California. Overnight lows in some places look more like typical highs for this time of year, according to weather.com. Heat advisories are also out for parts of central California, where temperatures could threaten the elderly, children and those without air conditioning. Officials advise staying in air-conditioned spaces, drinking more water than usual and moving outdoor activities to early morning or late evening. The culprit is a persistent area of high pressure sitting over the West, which is expected to linger through the week. The Climate Prediction Center’s 6-to-10-day outlook keeps a bullseye of above-average warmth over the Southwest. October temperature outlooks favour above-normal readings for nearly all areas west of the Continental Divide, with the highest chances over California, western Nevada and southern Oregon. There is little relief on the horizon, forecasters say.