<P> Los Angeles is a hot - summer mediterranean climate (Köppen Csa), with hot, dry summers, and cooler wetter winters . While the typical dry - summer and wet - winter pattern typical of most Mediterranean climates is part of the climate of Los Angeles, precipitation annually is lower than many typical Mediterranean climates . </P> <P> The summer dry season normally runs from June through October, when clear skies, hot temperatures, and very little change in sensible weather occur from day to day . Average high temperatures are in the lower 80's F (26 - 28 C) with overnight lows in the lower 60's F (15 - 17 C). During this season, there is essentially no rainfall, and both July and August average less than 0.05 of a inches (1.27 mm) of monthly precipitation . </P> <P> The winter wet season normally runs from November through early May . Precipitation episodes in Los Angeles, with a few notable exceptions, are largely caused by extratropical disturbances approaching California from the west or northwest during the winter season . The normal seasonal rainfall measured at downtown Los Angeles is 14.77 inches, of which 92% falls between November 1st and April 30th . While there is a great increase in rainfall in the winter months, the winter months in the Los Angeles are still frequently sunny and pleasant with mild temperatures . The average highs range from the upper 60's F to 70 F (17 - 21 C) with cooler overnight lows in the upper 40's and lower 50's F (8 - 12 C). </P> <Table> Climate data for Los Angeles (USC, Downtown), 1981--2010 averages, records 1877--present <Tr> <Th> Month </Th> <Th> Jan </Th> <Th> Feb </Th> <Th> Mar </Th> <Th> Apr </Th> <Th> May </Th> <Th> Jun </Th> <Th> Jul </Th> <Th> Aug </Th> <Th> Sep </Th> <Th> Oct </Th> <Th> Nov </Th> <Th> Dec </Th> <Th> Year </Th> </Tr> <Tr> <Th> Record high ° F (° C) </Th> <Td> 95 (35) </Td> <Td> 95 (35) </Td> <Td> 99 (37) </Td> <Td> 106 (41) </Td> <Td> 103 (39) </Td> <Td> 112 (44) </Td> <Td> 109 (43) </Td> <Td> 106 (41) </Td> <Td> 113 (45) </Td> <Td> 108 (42) </Td> <Td> 100 (38) </Td> <Td> 92 (33) </Td> <Td> 113 (45) </Td> </Tr> <Tr> <Th> Average high ° F (° C) </Th> <Td> 68.2 (20.1) </Td> <Td> 68.6 (20.3) </Td> <Td> 70.2 (21.2) </Td> <Td> 72.7 (22.6) </Td> <Td> 74.5 (23.6) </Td> <Td> 78.1 (25.6) </Td> <Td> 83.1 (28.4) </Td> <Td> 84.4 (29.1) </Td> <Td> 83.1 (28.4) </Td> <Td> 78.5 (25.8) </Td> <Td> 72.8 (22.7) </Td> <Td> 67.7 (19.8) </Td> <Td> 75.2 (24) </Td> </Tr> <Tr> <Th> Daily mean ° F (° C) </Th> <Td> 58.0 (14.4) </Td> <Td> 58.9 (14.9) </Td> <Td> 60.6 (15.9) </Td> <Td> 63.1 (17.3) </Td> <Td> 65.8 (18.8) </Td> <Td> 69.2 (20.7) </Td> <Td> 73.3 (22.9) </Td> <Td> 74.3 (23.5) </Td> <Td> 73.1 (22.8) </Td> <Td> 68.6 (20.3) </Td> <Td> 62.4 (16.9) </Td> <Td> 57.6 (14.2) </Td> <Td> 65.4 (18.6) </Td> </Tr> <Tr> <Th> Average low ° F (° C) </Th> <Td> 47.8 (8.8) </Td> <Td> 49.3 (9.6) </Td> <Td> 51.0 (10.6) </Td> <Td> 53.5 (11.9) </Td> <Td> 57.1 (13.9) </Td> <Td> 60.3 (15.7) </Td> <Td> 63.6 (17.6) </Td> <Td> 64.1 (17.8) </Td> <Td> 63.1 (17.3) </Td> <Td> 58.7 (14.8) </Td> <Td> 52.0 (11.1) </Td> <Td> 47.5 (8.6) </Td> <Td> 55.7 (13.2) </Td> </Tr> <Tr> <Th> Record low ° F (° C) </Th> <Td> 28 (− 2) </Td> <Td> 28 (− 2) </Td> <Td> 31 (− 1) </Td> <Td> 36 (2) </Td> <Td> 40 (4) </Td> <Td> 46 (8) </Td> <Td> 49 (9) </Td> <Td> 49 (9) </Td> <Td> 44 (7) </Td> <Td> 40 (4) </Td> <Td> 34 (1) </Td> <Td> 30 (− 1) </Td> <Td> 28 (− 2) </Td> </Tr> <Tr> <Th> Average rainfall inches (mm) </Th> <Td> 3.12 (79.2) </Td> <Td> 3.80 (96.5) </Td> <Td> 2.43 (61.7) </Td> <Td> 0.91 (23.1) </Td> <Td> 0.26 (6.6) </Td> <Td> 0.09 (2.3) </Td> <Td> 0.01 (0.3) </Td> <Td> 0.04 (1) </Td> <Td> 0.24 (6.1) </Td> <Td> 0.66 (16.8) </Td> <Td> 1.04 (26.4) </Td> <Td> 2.33 (59.2) </Td> <Td> 14.93 (379.2) </Td> </Tr> <Tr> <Th> Average rainy days (≥ 0.01 in) </Th> <Td> 6.1 </Td> <Td> 6.4 </Td> <Td> 5.5 </Td> <Td> 3.2 </Td> <Td> 1.3 </Td> <Td> 0.6 </Td> <Td> 0.3 </Td> <Td> 0.3 </Td> <Td> 1.0 </Td> <Td> 2.5 </Td> <Td> 3.3 </Td> <Td> 5.2 </Td> <Td> 35.7 </Td> </Tr> <Tr> <Th> Mean monthly sunshine hours </Th> <Td> 225.3 </Td> <Td> 222.5 </Td> <Td> 267.0 </Td> <Td> 303.5 </Td> <Td> 276.2 </Td> <Td> 275.8 </Td> <Td> 364.1 </Td> <Td> 349.5 </Td> <Td> 278.5 </Td> <Td> 255.1 </Td> <Td> 217.3 </Td> <Td> 219.4 </Td> <Td> 3,254.2 </Td> </Tr> <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> </Table>

6. the primary cause of wet winters in southern california is