Phoenix In December Is Not What You Think
December in Phoenix averages a high of 70°F and a low of 48°F. That's the textbook numbers. The reality is a little more complicated because the desert doesn't follow averages the way cities do. You'll get sunny mornings that feel like spring, then suddenly the wind shifts and it drops to the low 40s by evening. This happens regularly enough that I stopped treating single-day forecasts as gospel about eight years ago. The packing list for December should be built around layering, not bulk. A light long-sleeve shirt, a fleece or light sweater, and a windbreaker are enough for most days. I still keep a heavier jacket in my closet for the few nights the temperature dips into the low 30s. That usually happens once or twice between mid-December and the first week of January, and if you're not prepared it catches you off guard. Bring sunglasses. The sun intensity doesn't change just because it's winter, and the daytime glare on the pavement is genuinely harsh even at lower sun angles. A wide-brimmed hat helps too if you plan on walking outside during midday. Most indoor places don't run their heating that aggressively since the days stay mild, so the layers matter more than thermal weight.
Daily Conditions Breakdown
Mornings are clear. I can say that with reasonable confidence because the monsoon season ends in September and by December the air is dry enough that cloud cover is the exception, not the rule. You'll see temps in the mid-40s to low 50s right after sunrise. By 10am they climb into the high 50s or low 60s, and they peak somewhere around 70°F in the early afternoon. After 4pm the temperature starts falling, and by 8pm you're often down into the upper 40s. Rainfall in December averages about 0.8 inches for the month, which sounds like nothing until you realize the ground is so dry that when it does rain, it runs off instead of soaking in. Flash flooding warnings aren't common in December but they're not impossible. I got caught near Scottsdale a couple winters back during a light drizzle that turned into a standing water situation on the road within twenty minutes. Not dramatic, but annoying enough that I learned to check radar before heading out. Snow is essentially zero. The nearest chance I've seen is a dusting of graupel at most, and that's maybe once every decade in the city proper. Don't pack for snow. Pack for temperature swings and dry skin.
What Beginners Mess Up
The biggest mistake people make is assuming December means winter gear. It doesn't. You'll see visitors arriving with heavy coats and then wearing them at 65°F in the shade. Meanwhile, the things nobody brings are moisturizer, lip balm, and a reusable water bottle. The humidity can drop below 20% and your skin feels it immediately. I used to blow that off until my hands started cracking in late November during a visit. Now I pack lotion and balm the same way I'd pack socks. Another thing people underestimate is the wind. November through February is when the cold fronts roll down from the Rockies and push through the basin. You can go from calm and 65°F to gusty and 45°F in under two hours. A light windbreaker solves half your problems. A scarf or neck gaiter solves the other half if you're sensitive to that kind of exposure.
Get the Full Details
Practical Temperature Ranges
Here's the useful breakdown. Early December sits a bit warmer, averaging highs in the low-to-mid 70s and lows in the low 50s. Mid-December is where things split. Some years you get a sustained warm spell, other years a strong front drops overnight temperatures into the upper 30s. Late December trends cooler again, with highs around 68°F and lows dipping into the upper 30s on the worst nights. If you're visiting, target the first two weeks for the most forgiving weather, or commit to the layering strategy if you're here later. UV index stays moderate to high throughout the month. Even on overcast days the desert sun punches through. I check SPF before I leave the house now, and not just for my face, because I noticed I was getting sunburn on my forearms during morning walks. That shouldn't happen in December if you're used to a different climate, but it does.
Activity-Specific Notes
Hiking is excellent this time of year because the trails aren't dangerously hot. Start early though. A noon hike in December can still hit 72°F or so with the sun bearing down. Water consumption matters less than summer but you still lose moisture through the dry air without feeling it. My rule of thumb is half a liter per hour for moderate activity, minimum. Downtown Phoenix stays a few degrees warmer than the surrounding desert basins due to the urban heat island effect. If you're walking around the Arts District or Old Town Scottsdale in the evening, it'll feel noticeably more comfortable than the trailheads. That said, parking lots and open desert areas cool faster. I learned this by sitting in a car at McDowell Mountain Regional Park at 7pm and actually needing a light jacket I hadn't brought along. Cactus locations and desert preserves are beautiful but exposed. There's very little shade at the desert botanic gardens in December. Bring a hat and schedule your visit between 9am and 12pm, then move somewhere with cover for lunch if the sun gets aggressive. I find that the best light for photos is mid-morning to just before noon. After that the shadows flatten and everything looks washed out.
The One Thing Nobody Warns You About
Desert plants look dormant but they're still doing things. Sage, creosote, and other local species release compounds into the air when the temperature drops quickly in the evening. It's not a pollutant issue, but if you have any respiratory sensitivity you might notice it. I used to get these weird throat irritation episodes that I couldn't explain until I read about creosote bushes releasing terpenes after cold fronts pass through. Seems minor until your sinuses are inflamed and you're wondering why you feel terrible on a perfect day. That said, the air quality in Phoenix is generally better in December than any other month. No monsoon dust, no summer ozone peaks. If you're coming for clear air and good visibility, this is the window. Just dress for what's happening at dawn, not what the forecast says at 2pm.
