Climate Overview
Kathmandu sits in a fertile bowl at an elevation of approximately 1,400 meters (4,600 feet), creating a temperate, subtropical highland climate. Unlike the sizzling plains of southern Nepal (the Terai) or the frozen peaks of the high Himalayas, Kathmandu stays relatively mild. However, its weather is defined by extreme seasonal shifts in rainfall and air quality, driven primarily by the South Asian monsoon.
Seasonal Trends
- Spring (March to May): This is a period of rapid warming. March begins with crisp mornings (around 10°C / 50°F) and pleasant afternoons. By May, temperatures often climb to 30°C (86°F). This season is characterized by a gradual buildup of "afternoon haze" as dust and pre-monsoon heat gather in the valley.
- Summer / monsoon (June to September): The monsoon typically arrives in mid-June. It is warm (28°C / 82°F) and intensely humid. While it doesn't rain 24/7, heavy downpours—often at night or in the late afternoon—account for about 80% of the city’s annual precipitation. The rain washes away the dust, leaving the valley incredibly lush and green.
- Autumn (October to November): Regarded as the "perfect" season. After the rains clear, the air is scrubbed clean, offering the sharpest views of the Himalayas from the valley rim. Daytime temperatures are a comfortable 20°C–25°C (68°F–77°F), with cool, refreshing evenings.
- Winter (December to February): Winters are dry and sunny but sharply cold at night. While daytime highs reach 18°C (64°F) under clear skies, nighttime lows frequently drop near freezing (3°C / 37°F). Frost is common in the early mornings, though snow in the city center is an extremely rare historical event.
Daily Rhythm and Thermal Behavior
Kathmandu follows a distinct diurnal pattern, especially in the dry season.
- Mornings: Can be misty or foggy, especially in winter. Shadows remain chilly until the sun clears the surrounding hills around 9:00 AM.
- Afternoons: The valley floor heats up quickly. Even in winter, the direct Himalayan sun feels much warmer than the air temperature suggests. In the pre-monsoon spring, afternoons often bring strong "thermal winds" that kick up dust.
- Evenings: As soon as the sun dips behind the mountains (around 5:30 PM to 6:00 PM), the temperature drops rapidly. This "temperature cliff" is a defining feature of the Kathmandu experience.
Specific Weather Phenomena
- Temperature Inversions: During winter, cold air becomes trapped on the valley floor by the surrounding mountains. This prevents smoke and dust from escaping, leading to a visible layer of smog and decreased air quality until the sun warms the ground enough to break the inversion.
- The Valley Fog: In December and January, a thick morning fog often blankets the city, occasionally delaying flights at Tribhuvan International Airport. This fog usually burns off by mid-morning.
- Pre-Monsoon Thunderstorms: In late April and May, the heat often breaks with sudden, violent afternoon thunderstorms accompanied by hail and gusty winds.
Local Experience and Adaptation
Locals live by the sun. In winter, you will see residents sitting outside on "muda" (traditional stools) or rooftops to soak up the afternoon sun—a practice known as gham tapne. Architecture traditionally focuses on keeping heat out during the summer, meaning many older brick buildings feel colder inside than outside during the winter.
What the Weather "Feels Like"
- The Sun’s Power: Due to the altitude and thinner atmosphere, the sun feels intense. A 20°C day in Kathmandu feels warmer than 20°C in London or New York.
- Air Quality Factor: In the dry months (Jan–May), the weather often feels "dusty" or "heavy" due to urban pollution. Conversely, the post-monsoon air (October) feels incredibly light, crisp, and "high-definition."
- Moisture: During the monsoon, the humidity makes the heat feel "sticky," and the dampness can make indoor spaces feel cooler than the actual temperature.