<Tr> <Th> Percent possible sunshine </Th> <Td> 71 </Td> <Td> 72 </Td> <Td> 72 </Td> <Td> 78 </Td> <Td> 64 </Td> <Td> 64 </Td> <Td> 83 </Td> <Td> 84 </Td> <Td> 75 </Td> <Td> 73 </Td> <Td> 70 </Td> <Td> 71 </Td> <Td> 73 </Td> </Tr> <Tr> <Td_colspan="14"> Source: NOAA (sun 1961--1977) </Td> </Tr> <P> Summers are warm to hot, and nearly completely dry . The summer temperature pattern usually begins in late June or early July, and lasts through September or October, although it may start as early as late May . In August, the average high / low at the University of Southern California downtown campus are 84.8 ° F (29.3 ° C) and 65.6 ° F (18.7 ° C). The same figures at the LAX airport, approximately 12 miles (19 km) to the southwest and near the ocean, are 76.6 ° F (24.8 ° C) and 64.2 ° F (17.9 ° C). However, temperatures across the region sometimes exceed 90 ° F (32 ° C) during the summer . This happens when an atmospheric high - pressure area becomes dominant over the Great Basin of Nevada and Utah (a frequent occurrence), and the resulting offshore flow of the atmospheric air mass shuts off the normal coastal sea breeze in Los Angeles . July, August and September are the hottest months, with September holding the all - time record of 113 ° F (45 ° C). Skies are nearly constantly sunny, unless interrupted in late spring and early summer by the June Gloom pattern, which is unpredictable year - to - year . The North American Monsoon can bring occasional thunderstorms and high humidity to Los Angeles in the summer and early fall . </P> <P> Winters are mildly cool to warm, with average high temperatures at the Downtown / USC weather station of 68 ° F (20 ° C) and lows of 48 ° F (9 ° C), with occasional heavy rainfall . Temperatures across the coastal basin rarely drop below 45 ° F (7 ° C), although light frost does occasionally form during cooler nights, at least in areas removed from the direct influence of the coastal air (approximately 5 miles (8 km) inland from the beach). However, high pressure systems over the deserts often bring some Santa Ana winds, resulting in dry, and dusty days . Temperatures can reach into the 70 to 85 ° F (21 to 29 ° C) routinely during Santa Ana Winds even in December or January but only sometimes . Almost every winter season, temperatures can usually reach up to75 ° F (24 ° C) but can reach up to 85 ° F (29 ° C) on some days during a Santa Ana - type event . Sunny skies characteristically dominate the weather pattern in some parts of the winter season . </P>

When does the weather warm up in los angeles