The climate of Los Angeles is classified as a Subtropical Mediterranean type, characterized by abundant sunshine throughout the year. The defining feature is the distinct seasonal distribution of moisture: long, warm, and exceptionally dry summers, followed by mild and relatively wet winters that concentrate annual rainfall into a short period.
Defining the Mediterranean Climate and Seasonal Rhythm
Summers are consistently warm and arid, with downtown Los Angeles typically seeing average high temperatures around 84°F in the warmest month, August. Nighttime lows during this period are mild, averaging about 66°F. The summer months are almost entirely rainless, with July and August averaging essentially zero inches of precipitation.
The lack of summer rain results in low humidity and clear skies. The transition into autumn remains warm and dry, with the driest conditions persisting until late fall.
The cool season (late fall through early spring) is when nearly all of the region’s moisture is received. The average high temperature in the coldest month, December, is a mild 67°F, with overnight lows dropping to an average of about 48°F. Annual precipitation totals average between 14.2 to 14.93 inches.
Rainfall is infrequent but highly concentrated, with approximately 92% of the annual total falling between November and April. February is often the wettest month, averaging around 3.5 inches of rain. Despite being the “wet season,” winter months still feature frequent sunny days and pleasant temperatures, differentiating this climate from many other temperate zones.
Geographical Influence: Los Angeles’ Diverse Microclimates
The Los Angeles metropolitan area experiences a wide range of weather conditions due to its varied topography, creating distinct microclimates. The proximity of the Pacific Ocean and significant mountain ranges drive these variations, acting as thermal dividing lines that cause temperature differences over short distances.
The Coastal Zone
The Coastal Zone benefits directly from the moderating influence of the Pacific Ocean. Areas within a few miles of the shore, such as Santa Monica, experience the coolest temperatures and the least seasonal variation. This marine influence often brings cool, moist air and higher humidity, helping to regulate summer heat and keep temperatures moderate.
Inland Valleys
Moving inland, away from the ocean’s cooling effect, the Inland Valleys such as the San Fernando Valley, experience much greater temperature swings. Without the marine layer’s moderation, summer days can be significantly hotter, sometimes reaching 80°F or more while the coast remains in the low 60s. Winters here are also slightly cooler than on the coast, illustrating a more continental temperature pattern.
Mountain and Foothill Areas
The difference in daytime temperatures between the coast and the inland areas can be as great as 36°F on the same day. The mountain ranges, including the Santa Monica and San Gabriel Mountains, block the cool, dense Pacific air from penetrating far into the valleys, which allows inland temperatures to climb. Higher-elevation Mountain and Foothill Areas experience the most pronounced temperature extremes and are the only parts of the county that occasionally see snowfall in the winter months.
Signature Weather Phenomena
One phenomenon is “May Gray” or “June Gloom,” which occurs in the late spring and early summer, caused by a low-lying marine layer that forms over the cool Pacific waters. This layer of cool, moist air creates morning fog and low clouds, often blanketing coastal areas. While this is a temporary condition, it delays the arrival of sunshine, sometimes lingering until midday before the sun burns through and clears the clouds.
Another defining event is the Santa Ana winds: strong, extremely dry, down-sloping winds. They originate from high-pressure systems building over the Great Basin, which force air to flow toward the coast and through mountain passes. As this air descends, it is compressed, causing it to warm significantly and lose moisture, a process known as adiabatic heating.
These winds are most common in the fall and winter, bringing the lowest relative humidity of the year to the coastal areas. The combination of warmth, dryness, and high wind speed creates extreme fire weather conditions. The Santa Ana winds fan existing wildfires, allowing them to spread rapidly and creating the region’s fire risk.