Siwan has a warm subtropical climate with warm summers and mild winters.
Temperatures peak in May and drop to their lowest in January, while rainfall is highest during summer months.
Humidity remains relatively low throughout the year, especially in autumn, creating warm and dry conditions.
| Month | 🌤️ | High | Low | Avg | Humid % | Rain (mm) | Wind (m/s) | Solar (kWh/m²) |
|---|---|---|---|---|---|---|---|---|
| January | ☀️ | 28.2°C | 4.9°C | 16.6°C | 48% | 10 | 1.6 | 3.20 |
| February | ☀️ | 33.6°C | 7.1°C | 20.4°C | 39% | 12 | 1.9 | 4.60 |
| March | 🌞 | 40.2°C | 11.8°C | 26.0°C | 28% | 9 | 2.2 | 5.82 |
| April | 🔥 | 44.2°C | 18.7°C | 31.5°C | 23% | 13 | 2.4 | 6.53 |
| May | 🔥 | 45.8°C | 23.7°C | 34.7°C | 31% | 43 | 2.5 | 6.51 |
| June | ☔ | 45.1°C | 26.4°C | 35.7°C | 47% | 139 | 2.8 | 5.76 |
| July | 🌧️ | 38.7°C | 25.5°C | 32.1°C | 75% | 287 | 2.7 | 4.75 |
| August | 🌧️ | 35.1°C | 24.7°C | 29.9°C | 83% | 245 | 2.3 | 4.80 |
| September | 🌧️ | 33.9°C | 22.1°C | 28.0°C | 84% | 175 | 2.0 | 4.60 |
| October | 🌞 | 33.2°C | 15.6°C | 24.4°C | 72% | 48 | 1.3 | 4.62 |
| November | ☀️ | 31.0°C | 10.2°C | 20.6°C | 59% | 4 | 1.2 | 3.94 |
| December | ☀️ | 27.7°C | 6.1°C | 16.9°C | 53% | 6 | 1.4 | 3.12 |
Showing average climate conditions across 45 years (1981–2025)
🧥 Light layers are sufficient — this Mild Winter stays cool without prolonged hard freezes.
🌤️ Limit midday outdoor exposure and stay hydrated — this is an intense Hot Summer.
☔ Heavy Rainfall expected — carry rain gear and plan outdoor activities around these months.
Monthly averages · 1981–2025 climate normals · °C
Temperatures rise steadily from spring, peak in May, and gradually decline through autumn into winter.
These seasonal patterns offer comfortable conditions year-round, with warm summers and mild winters.
Monthly rainfall · 1981–2025 seasonal trends · mm/month
Monthly averages · 1981–2025
💧 Humidity peaks at 84% in September · annual avg 53%
The warmest year in Siwan's recorded history was 2023 (avg: 27.5°C), while the coldest was 2020 (avg: 24.9°C).
Average annual high/low · Last 10 years · °C
Total annual precipitation · Last 10 years · mm/year
| Year | Min Temp | Avg Temp | Max Temp | Rainfall (mm) | Avg Humidity | Avg Wind |
|---|---|---|---|---|---|---|
2025 | 17.2°C | 26.7°C | 36.1°C | 982 | 59% | 2.1 m/s |
2024 | 17.3°C | 27.2°C | 37.1°C | 796 | 55% | 2.1 m/s |
2023 | 17.8°C | 27.5°C | 37.1°C | 685 | 53% | 2.1 m/s |
2022 | 16.9°C | 26.5°C | 36.2°C | 754 | 60% | 2.1 m/s |
2021 | 16.2°C | 25.7°C | 35.1°C | 1317 | 63% | 2.0 m/s |
2020 | 15.4°C | 24.9°C | 34.5°C | 1288 | 65% | 1.9 m/s |
2019 | 16.5°C | 26.7°C | 37.0°C | 911 | 57% | 2.1 m/s |
2018 | 17.5°C | 27.4°C | 37.2°C | 659 | 49% | 2.1 m/s |
2017 | 17.0°C | 27.1°C | 37.3°C | 804 | 53% | 1.9 m/s |
2016 | 17.6°C | 27.4°C | 37.3°C | 827 | 53% | 2.0 m/s |
Showing 1 to 10 of 45 years
Based on 45 years of data (1981–2025), May is typically the hottest month in Siwan, Bihar, with average high temperatures around 45.8°C.
January is the coldest month in Siwan, with average low temperatures around 4.9°C.
July receives the most rainfall with approximately 287 mm, while November is the driest with 4 mm.
The highest recorded temperature was 48.5°C in May 1998. This is part of the historical record spanning 1981–2025.
The lowest recorded temperature was 1.3°C in January 2013.
This page covers 45 years of climate data from 1981 to 2025. As new data is added to the database the page automatically reflects the updated coverage.
Siwan receives the most sunlight in April with an average solar radiation of 6.53 kWh/m²/day. This solar radiation data, sourced from NASA POWER, is useful for solar energy planning and agriculture in Bihar.
All climate data is sourced from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite and model data. It provides monthly averages for temperature, precipitation, humidity, wind speed, and solar radiation.
All weather data is sourced from NASA POWER (Prediction of Worldwide Energy Resources), a NASA project providing solar and meteorological data for renewable energy, building efficiency, and agricultural research.
