The Subtropical Highland Reality
Mexico City’s climate is defined by two major factors: its tropical latitude and its extreme altitude (approximately 2,240 meters / 7,350 feet). This combination creates a "Subtropical Highland" climate, often described as a perpetual spring. Unlike the sweltering humid heat typically associated with Mexico's coasts, the capital remains temperate year-round, with low humidity and high solar intensity.
Daily Weather Rhythms
In Mexico City, the clock often dictates the weather more than the calendar.
- Morning: Generally crisp and cool. Even in the warmest months, the thin mountain air loses heat rapidly overnight, meaning mornings can feel brisk.
- Mid-day to Afternoon: Solar radiation is intense due to the altitude and thin atmosphere. Temperatures rise sharply, and the sun can feel significantly hotter than the thermometer suggest.
- Evening: As the sun sets, temperatures drop quickly. During the rainy season, the late afternoon (typically between 4:00 PM and 7:00 PM) marks the arrival of predictable, heavy downpours.
The Two Main Seasons
Instead of four distinct seasons, locals experience two primary cycles: the dry season and the wet season.
The Dry Season (November – April)
This is the most stable time of year. Skies are almost universally deep blue and cloudless.
- Early Dry (Winter): November to February sees the coolest temperatures. Nighttime lows can drop to 3°C–6°C (37°F–43°F), while daytime highs reach a pleasant 21°C–23°C (70°F–74°F).
- Late Dry (Spring): March and April are the hottest months of the year. Highs frequently hit 27°C–30°C (81°F–86°F). This is the sunniest period, but also the peak for air pollution as the lack of rain traps pollutants in the valley basin.
The Rainy Season (May – October)
Roughly 75% to 80% of the city's annual rainfall occurs during this window.
- The Rhythm: Mornings remain clear and sunny. In the late afternoon, dark clouds gather rapidly over the surrounding volcanoes, culminating in short, violent thunderstorms and heavy deluges.
- The Impact: These rains are refreshing—they drop the temperature and clear the air of smog—but they can cause localized street flooding. July and September are historically the wettest months.
Microclimates and Variations
Because the city sits in a volcanic basin, topography creates noticeable weather variations:
- The South and West: Neighborhoods like San Ángel, Coyoacán, and Ajusco are closer to the mountains and significantly higher in elevation. These areas receive more rainfall and are consistently 2°C–4°C cooler than the city center.
- The North and East: These flatter, lower-lying areas (near the airport and Teotihuacán) are drier and warmer, often experiencing more wind and dust during the dry season.
- Historical Context: Originally a lake-bed (Lake Texcoco), the city’s drainage has altered its humidity. The “Urban Heat Island” effect is strong in the dense concrete core, making the Zócalo feel warmer at night than more forested areas like Chapultepec.
Local Experience and Phenomena
- Adaptation: Locals often dress in layers to handle the 20-degree temperature swings between dawn and mid-afternoon. Carrying an umbrella in summer is a way of life, not a suggestion.
- Visibility: On the clearest dry-season days, the snow-capped volcanoes Popocatépetl and Iztaccíhuatl are visible from the city. In the rainy season, this visibility vanishes behind thick afternoon cloud banks.
- Altitude Adjustment: The thin air means UV exposure is much higher than at sea level. The "feels like" temperature in the sun is much higher than in the shade, where the air remains cool.
- Pollution & Smog: During the warm-dry transition (March-May), thermal inversions can trap ozone in the valley, leading to "Contingencia Ambiental" days where local outdoor activity is discouraged.