Southern California is enduring a third straight day of record-smashing temperatures as a powerful high-pressure system refuses to budge. The National Weather Service has issued an extreme heat warning for San Diego County's desert regions effective through 8 p.m. Saturday, March 21, with forecast highs of 104 to 112 degrees Fahrenheit -- temperatures more typical of June than mid-March.

Inland valleys and foothills, including the Santee and El Cajon areas, are under a heat advisory through Friday, with temperatures expected to reach the mid-90s to triple digits. Forecasters say temperatures this week are running 20 to 30 degrees above normal for mid-March, and the event is now on track to be the hottest March heat wave on record for the region.

Orange and San Diego counties broke 13 daily temperature records on Tuesday alone, according to the National Weather Service. Anaheim hit 100 degrees, shattering the prior record of 90 set in 2010. More records are expected to fall through Thursday and Friday, when forecasters say inland areas will reach peak temperatures.

For Santee residents without air conditioning, the Santee Branch Library at 9225 Carlton Hills Blvd. is designated as a Cool Zone. Residents who are homebound or have disabilities can call 211 to arrange free transportation to a cooling facility. Public health officials urge residents to stay hydrated, avoid strenuous outdoor activity during peak afternoon heat, and never leave children or pets in unattended vehicles.

Moderate relief is expected by this weekend, with a gradual dip in temperatures beginning Sunday as the high-pressure ridge flattens. Coastal marine layer clouds are expected to return Friday night, with noticeably cooler conditions across the region by Sunday.