December in Phoenix Arizona Weather Detailed Forecast and What To Expect

December in Phoenix marks a decisive shift from the extreme summer heat, as the desert city settles into its most comfortable season. Cool, sunny days, low humidity, and virtually zero rainfall define the month, making it a prime window for outdoor activity. This article examines historical trends, current expectations, and practical implications of Phoenix weather in December.

December serves as the definitive gateway to Phoenix’s most celebrated season, when diurnal temperature swings create ideal conditions for exploring the region’s desert landscape. Average highs retreat from the broiling spring and summer norms into a temperate range that supports hiking, golf, and evening events without the need for heavy clothing. Understanding the specifics of December weather allows residents and visitors to plan activities, dress appropriately, and anticipate the occasional outlier event that can still deliver summerlike warmth or an unusual cold snap.

The month consistently ranks among the most pleasant times of the year in the Valley of the Sun, drawing visitors and prompting seasonal relocations known as "snowbird" migrations. Yet even within this generally favorable framework, variability exists, influenced by broader climate patterns such as El Niño and the strength of the Pacific jet stream. A closer look at temperature normals, precipitation history, and emerging forecasts reveals what makes December in Phoenix distinctive and how to interpret day-to-day conditions.

Average high temperatures in Phoenix during December typically hover between 66 and 70 degrees Fahrenheit, depending on the specific dataset and year, while overnight lows usually fall between 43 and 47 degrees. These averages are calculated over three-decade normals, the standard reference used by climatologists and forecasters to define what conditions "usually" look like. For example, Phoenix Sky Harbor International Airport, the official climatology site for the metropolitan area, documents a long-term December average high of 67 degrees and an average low of 45 degrees.

Midday sun in December remains intense compared to many other U.S. cities experiencing winter, with average daily sunshine exceeding 300 hours across the month. Clear skies dominate the majority of days, driven by stable high pressure that typically settles over the Southwest during this season. Relative humidity is characteristically low, often averaging in the 30 to 45 percent range during the afternoon, though morning hours can feel more humid near irrigated landscapes and the Salt River vegetation corridors.

While rare, December can produce anomalously cold events when a strong front penetrates the region, dropping temperatures into the 30s or even near freezing at night. Such occurrences are infrequent and short-lived, but they underscore that Phoenix is still a desert climate capable of sharp contrasts. The city’s all-time December record low stands in the upper 20s, a reminder that frost and freeze advisories, while uncommon, are not impossible.

Precipitation in December is typically minimal, with the National Weather Service’s historical records indicating an average of just over an inch of rain for the month. Most of this moisture arrives via passing storm systems tapping into atmospheric rivers or Gulf moisture, often producing brief but occasionally heavy downpours. December also marks the beginning of Phoenix’s secondary rainy season, which extends into February, though the volume is dwarfed by the North American Monsoon of July and August.

The rain that does fall can be significant when it occurs, as the dry ground offers little immediate absorption. Street flooding is a common concern, particularly in low-lying areas and near washes, even from modest rainfall events. Residents and visitors alike are reminded that "a few drops" can translate into fast-moving water in urban drainage systems designed primarily for high-volume storm events.

For those planning outdoor activities, December offers one of the best windows of the year for hiking, biking, and sightseeing in and around Phoenix. Popular trails in areas like Camelback Mountain, South Mountain Park, and the McDowell Sonoran Preserve are frequently busy on mild afternoons. Garden visits, golf rounds, and open-air dining are also at their peak during this period, supported by reliable sunshine and moderate temperatures.

Planning ahead remains essential, as conditions can vary week to week. Checking detailed forecasts from authoritative sources such as the National Weather Service Phoenix Office allows for precise preparation, including decisions about layering clothing and scheduling strenuous activities for cooler morning hours. Those sensitive to heat or cold can still find comfortable outdoor times, particularly between late morning and early afternoon when temperatures are most benign.

Long-range forecasting tools, including the analysis of El Niño–Southern Oscillation (ENSO) phases, help predict whether a given December will trend warmer or cooler, wetter or drier than average. In an El Niño year, Phoenix often sees increased storm chances and slightly cooler temperatures, while La Niña patterns typically favor warmer and drier conditions. These patterns do not guarantee outcomes but provide a probabilistic framework for understanding monthly risks.

Ultimately, December in Phoenix represents a return to the moderate, sunny conditions that originally attracted settlers and growth to the region. It encapsulates the desert’s capacity for hospitality, offering comfortable days for exploration and crisp evenings suited for outdoor gatherings. By following the guidance of local meteorologists and respecting the potential for sudden weather shifts, residents and visitors can fully appreciate the unique advantages of wintertime in the Valley of the Sun.