LOS ANGELES –Southern Californiais set to swelter as a heat wave has prompted extreme heat warnings and heat advisories. Temperatures will hit the triple digits in parts of the Southland starting Wednesday, Aug. 20, with the Woodland Hills neighborhood of Los Angleses in the San Fernando Valley hitting 109 F on Thursday, Aug. 21. –according to a National Weather Service forecast. "SoCal is on the precipice of the hottest stretch of days so far this summer as the high pressure system over the desert southwest expands westward while at the same time onshore flow weakens," the NWS said ina forecast discussionissued just after 2 p.m. PT Aug. 19. Extreme heat warnings will be in effect on Thursday, Aug. 21, starting at 11 a.m. PT until Saturday, Aug. 23 at 9 p.m. PT in at least parts of San Luis Obispo, Santa Barbara, Ventura and Los Angeles counties. Orange County will be under a heat advisory beginning on Thursday, Aug. 21 from 10 a.m. PT until Friday, Aug. 22 at 8:00 p.m. PT. The NWS said that relief from the heat could come starting Monday as the high-pressure system will weaken in earnest, with highs dropping back to "near normal" Here's where heat warnings and advisories have been issued, and the three-day forecast fromAccuWeather. Forecast provided by AccuWeather Wednesday,Aug. 20 High: 90 F Feels like: 94 F Low: 68 F Average: 84 F Thursday,Aug. 21 High: 93 F Feels like: 97 F Low: 69 F Average: 84 F Friday,Aug. 22 High: 94 F Feels like: 101 F Low: 70 F Average: 84 F Wednesday,Aug. 20 High: 102 F Feels like: 104 F Low: 71 F Average: 96 F Thursday,Aug. 21 High: 105 F Feels like: 108 F Low: 71 F Average: 96 F Friday,Aug. 22 High: 103 F Feels like: 108 F Low: 68 F Average: 96 F Wednesday,Aug. 20 High: 91 F Feels like: 95 F Low: 66 F Average: 85 F Thursday,Aug. 21 High: 93 F Feels like: 98 F Low: 69 F Average: 85 F Friday,Aug. 22 High: 93 F Feels like: 102 F Low: 69 F Average: 85 F Wednesday,Aug. 20 High: 94 F Feels like: 98 F Low: 66 F Average: 92 F Thursday, Aug. 21 High: 100 F Feels like: 103 F Low: 70 F Average: 92 F Friday, Aug. 22 High: 99 F Feels like: 105 F Low: 66 F Average: 92 F This article originally appeared on USA TODAY:Heat warnings and advisories issued for Southern California heatwave