SAMPLE CLIMATOLOGICAL SUMMARY

The Los Angeles Basin covers a broad area of Los Angeles County which extends from metropolitan Los Angeles at the coast to the San Fernando and San Gabriel Valleys, and the San Gabriel Mountains in the interior of the County. The Pacific Ocean is the primary moderating weather influence across coastal Los Angeles County, keeping conditions relatively mild during the period mid-October through mid-November. The coastal mountain ranges lying along the north and east sides of the Los Angeles coastal basin act as a buffer against extremes of daytime heat and chilly nighttime conditions which can occur across desert and plateau regions in the interior during this period. An important, and somewhat unusual, aspect of the climate of the Los Angeles metropolitan area is the pronounced difference in temperature, humidity, cloudiness, fog, sunshine and rain over fairly short distances. This is due to the local topography and the decreased marine effect further inland.

In general, temperature ranges are least and humidity highest close to the coast, while precipitation increases with elevation on the foothills. Sunshine, fog, and clouds depend a great deal on topography and distance from the ocean. Low clouds are common at night and in the morning along the coast/beaches, but form later and clear earlier near the foothills so that annual cloudiness and fog frequencies are greatest near the ocean, and sunshine totals are highest on the inland side of the city and across the interior valleys. Light fog may accompany the usual night and morning low clouds, with dense fog (fog which restricts the visibility to 1/4 mile or less) occurring on an average of 2.5 days during the period mid-October through mid-November. In any event, fog (should it form) typically lifts or burns off by mid-morning, with sunshine the rule each afternoon. Overall sunshine is abundant with 74 percent of the possible amount occurring on the average during the period. Rainfall, which is scarce during late October begins to increase with the onset of the winter rainy season in November as the storm track from off the Pacific Ocean begins to shift toward southern California. Measurable rainfall occurs on an average of 2 to 3 days and averages 1.15 inches for the period, most of which occurs during the first half of November. Thunderstorm activity is uncommon during this period, but has occurred in the past. Temperatures given previously are the averages for the Los Angeles Civic Center, which is located approximately 12 miles inland to the northeast of the Pacific Coast. Average daily high temperatures are some 5 to 10 degrees cooler at the ocean beaches, and 10 degrees or higher across the San Fernando and San Gabriel Valleys. Average daily low temperatures are approximately the same at the ocean beaches, and approximately 5 to 10 degrees cooler across the San Fernando and San Gabriel Valleys. Late October typically marks the end of the hottest weather, with the most intense heat usually confined to the valleys with daytime readings in excess of 100 degrees Fahrenheit (F) not uncommon during late October. Temperature extremes of near 110 F have been recorded in October and near 100 F in November, as well as lows in the 30’s F in past years. One other aspect of Los Angeles weather which is unique to southern California, is occasional foehn-like descending winds known as "Santa Anas". These winds originate from the northeastern high deserts of southern California and blow over ridges and through passes in the coastal mountains as they descend into the Los Angeles Basin. These winds may pick up considerable dust and reach speeds of 35 to 50 mph or more in north and east sections of the city, higher in outlying areas to the north and east, however they rarely reach the ocean.
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