Weather In L.A In December: Be Ready For Mild Days, Cool Nights, And Occasional Storms
December in Los Angeles marks the definitive shift from the mild autumn season into the heart of winter, a time when the city trades the intense heat of summer for more moderate, though still nuanced, climatic conditions. It is a month characterized by a distinct dichotomy, where daytime temperatures often permit light outdoor attire while evenings necessitate layers, and the rainy season typically begins its annual arrival. This period ushers in the region’s primary rainfall and a noticeable dip in temperatures, offering residents and visitors a different perspective on the city that is far removed from its sun-drenched, beach-centric image.
The climatic transition in December is underpinned by fundamental atmospheric dynamics that steer the region’s weather patterns. As the Northern Hemisphere tilts away from the sun, the angle of sunlight decreases, resulting in shorter days and a corresponding drop in solar energy reaching the surface. Concurrently, the vast Pacific Ocean, which exerts a significant moderating influence on the coastal and inland areas, begins to interact with the encroaching winter weather systems moving south from the Gulf of Alaska. These interactions form the basis for the seasonally typical conditions observed across the diverse topography of the Los Angeles basin.
The average weather data for December provides a clear, statistical baseline for what residents can generally expect. While daily fluctuations are common, and some years may present unusual warm "Santa Ana" episodes or extended dry spells, the following figures define the month’s climatic norms. These averages are derived from decades of meticulous observation compiled by the National Weather Service and other meteorological institutions.
* **Average High Temperature:** Approximately 68°F (20°C). This represents a comfortable, sweater-weather temperature for outdoor activities during the midday and afternoon hours.
* **Average Low Temperature:** Around 48°F (9°C). This significant drop after sunset underscores the importance of layering, as the urban heat island effect can make inland valleys noticeably colder.
* **Average Precipitation:** Roughly 3 to 4 inches (76-102 mm) spread across the month. This moisture is vital for replenishing the region's reservoirs and sustaining its Mediterranean ecosystem.
* **Average Humidity:** Typically ranging from 60% to 75%, creating a crispness in the air that is characteristic of Southern California winters.
* **Average Sunshine Duration:** Approximately 6 to 7 hours of daily sunshine, a substantial decrease from the summer months but still offering ample daylight for activities.
The geography of Los Angeles plays a crucial role in shaping the specific weather experience from one neighborhood to another. The city’s sprawling landscape, which stretches from the Pacific coastline to the San Gabriel Mountains, creates a complex mosaic of microclimates that dictate temperature, wind, and precipitation. December serves as a prime example of this topographical influence.
* **Coastal Zones:** Areas like Santa Monica, Venice, and Malibu benefit from the moderating effect of the Pacific Ocean. These locations experience milder temperatures, with highs often hovering in the mid-60s to low 70s°F, and are more frequently visited by coastal stratus clouds, locally known as "May Gray" or "June Gloom," which can create a cool, gray atmosphere in the mornings that often burns off by afternoon.
* **Inland Valleys:** San Fernando Valley and communities further east, such as Burbank and Glendale, tend to be cooler, particularly at night. The absence of the ocean's thermal inertia allows for greater temperature swings, with daytime highs potentially reaching the upper 60s to low 70s but nighttime lows often dipping into the high 40s.
* **Mountain and Foothill Regions:** The Santa Monica Mountains and the San Gabriel Mountains act as physical barriers, forcing moisture-laden air upwards. As this air rises, it cools and condenses, leading to significantly higher rainfall totals in these elevated areas. Snow at higher elevations is not uncommon, while the lower elevations experience the rain.
December is the month when Los Angeles truly enters its rainy season, which conventionally runs from November through March. While major atmospheric river events can occur at any point during this period, December often serves as the season's powerful opening act. These "Pineapple Express" storms, named for the warm, moisture-laden air streams that originate near Hawaii, are capable of delivering days' worth of rain in a matter of hours.
These atmospheric rivers are not merely spectacle; they are critical to the region's water management. "We closely monitor the atmospheric river patterns in December, as they are fundamental to our annual water supply," explains a senior meteorologist with the National Weather Service's Los Angeles office. "While they can cause significant localized flooding, the precipitation they deliver is essential for filling our reservoirs and securing water resources for the coming year." The interplay between these intense storm systems and the region's historic flood control infrastructure defines a great deal of the December weather narrative.
For the millions of residents and the countless tourists who remain in the city during December, the weather dictates a distinct rhythm of life. The shift from summer lethargy to a more active, sometimes volatile, winter mood is palpable. Outdoor enthusiasts take advantage of the milder days for hiking in the Santa Monica Mountains or along the coast, when the skies are clear. The holiday season itself is partially shaped by the weather, with backyard gatherings and outdoor festivities possible during the day, but requiring blankets and heaters as the sun dips below the horizon.
The potential for severe weather also necessitates a certain level of public preparedness. While the image of Los Angeles as perpetually sunny and warm is iconic, the reality is a city that adapts to a wetter, cooler season. Residents routinely keep rain jackets and umbrellas in their cars, a practical response to the season’s unpredictability. Schools and businesses may rarely close for weather, but the collective consciousness shifts to acknowledge the presence of rain, a phenomenon that can sometimes feel as novel to Southern Californians as it is routine for the rest of the country.
