Los Angeles Weather December: Your Guide to the City’s Coolest Month

December in Los Angeles signals a distinct slowing of the year. While famous for sunshine, the City of Angels enters its cool season, bringing lower temperatures, increased rainfall, and the rare chance of witnessing frost in the mountains. This is the month when the tourist crowds thin, the landscape deepens in color, and residents trade beach trips for evening fires and mountain views.

The transition from autumn to winter is subtle but measurable. Average highs retreat from the 70s into the upper 60s, and the relentless dry heat of summer is replaced by a more temperate, sometimes damp, climate. For anyone planning a visit or simply adjusting to the local rhythm, understanding these shifts is essential to navigating the season.

December marks the astronomical start of winter in the Northern Hemisphere, occurring on the winter solstice—the shortest day of the year—around December 21. The reduced angle and intensity of sunlight are the primary drivers behind the drop in temperature and the shortening of daylight hours. While the city rarely experiences freezing conditions at sea level, the change in solar radiation is the unseen hand reshaping the daily weather pattern.

This period is also the onset of the region’s rainy season, which typically runs from November through March. The shift is part of the larger atmospheric river cycle that delivers the majority of the area’s annual precipitation. These “Pineapple Express” storms, drawing moisture from the tropical Pacific, are the critical weather events that define the winter months.

### Temperature Trends and Daily Ranges

Daytime temperatures in December average in the upper 60s Fahrenheit, a noticeable dip from the summer’s scorching peaks. Nighttime lows often fall into the mid-40s to low 50s, creating a pronounced daily swing. This variation means that layering clothing is not just a fashion choice but a practical necessity.

Specific districts experience microclimates that can dramatically alter the feel of the day. While downtown might be a mild 68°F, the San Gabriel Valley foothills can be 15 degrees cooler, and the beach areas often remain a few degrees warmer due to the thermal moderation of the Pacific. Santa Monica, for instance, frequently reports higher humidity and stronger marine layer influence than communities in the Valley.

Here is a comparative look at average December temperatures across different zones of the greater Los Angeles area:

* **Coastal Zones (Santa Monica, Venice, LAX):** Average High 66°F (19°C), Average Low 49°F (9°C)

* **Westside & Downtown:** Average High 68°F (20°C), Average Low 48°F (9°C)

* **San Fernando and San Gabriel Valleys:** Average High 67°F (19°C), Average Low 41°F (5°C)

* **Mountain Communities (Griffith Park, Hollywood Hills):** Average High 64°F (18°C), Average Low 39°F (4°C)

These numbers are averages; extremes do occur. Cold snaps, often associated with strong Santa Ana winds pushing south from the interior, can drop temperatures into the 40s across the basin, while heat waves in December, though rare, have been recorded when high-pressure systems stagnate off the coast.

### Rainfall and Atmospheric Rivers

Precipitation is the defining weather variable of Los Angeles in December. The month is the second wettest of the year, averaging around 3 to 4 inches of rain. This might not sound like much compared to other climates, but it represents a significant portion of the annual total delivered in a short window.

The intensity of these storms varies. A typical rainy December day might see a gentle, steady drizzle lasting for hours. More dramatic events are atmospheric rivers—long, narrow corridors of concentrated moisture in the atmosphere—that can unleash several inches of rain in a single day. These events are critical for replenishing reservoirs and aquifers but also carry the risk of flash flooding in burn scars and low-lying areas.

December storm systems often arrive in sequences, known as an "atmospheric river train," where successive storms follow one another within days. This pattern keeps the soil saturated and increases the likelihood of secondary hazards like landslides, particularly in areas denuded by wildfires. The city’s emergency services and public works departments operate on high alert during this season, monitoring creek levels and drainage systems constantly.

### Ocean, Beach, and Mountain Conditions

The ocean temperature in December hovers in the mid-50s Fahrenheit. While technically swimmable for the hardiest, most beachgoers opt for alternative activities. Surfing, however, reaches a prime state. Winter swells generated by storms in the North Pacific build powerful, consistent waves that attract professional surfers to spots like Huntington Beach and Malibu.

In the mountains, the story is different. While snowfall in the city is a decades-long rarity, the higher elevations of the San Gabriel Mountains reliably receive dustings of snow. Occasional storms can dump significant accumulation, transforming the usually arid foothills into a winter playground. Mount Baldy (Baldy Bowl) and areas near Big Pines become destinations for sledding and snowshoeing.

For the coastal visitor, the marine layer—often called "June Gloom" but persistent in winter—is a frequent visitor. This cool, foggy layer rolls in from the ocean, blanketing the beachfronts in gray and dampness by morning. However, the pattern is often transient; by afternoon, the sun frequently burns through the layer, creating a clear, crisp environment perfect for hiking or sightseeing.

### Holiday Events and Urban Rhythm

The weather directly influences the texture of the holiday season in LA. While the city hosts numerous outdoor events, they are often planned with contingencies for cooler evenings. The holiday light displays at venues like the Hollywood Bowl or Griffith Observatory are best viewed under the clear, cold nights that December often provides.

Travel during the month is a study in contrasts. The beaches are largely empty, offering a rare solitude for those who visit. The warm, dry Santa Ana winds—locally known as "Santa Anitas"—can create unseasonably pleasant days perfect for exploring the city's parks and gardens without the summer heat. Yet, these same winds can exacerbate fire danger and contribute to the season's characteristic smoky haze on occasion.

Ultimately, December in Los Angeles is a month of adjustment. It is a time when the city trades its sandals for sneakers, its beach towels for blankets, and its focus from tourist spectacle to local life. Understanding the mechanics behind the seasonal shift—from the astronomical tilt to the arrival of atmospheric rivers—allows residents and visitors alike to appreciate the city’s winter not as a deficiency of summer, but as a distinct and beautiful chapter in its annual climate story.