Siwan climate
Siwan (Bihar, India) has a monsoon-influenced humid subtropical climate (Köppen Cwa). The average temperature over the year is 26 °C79 °F, and about 1,012 mm40 in of precipitation falls in an average year.
Temperature by month
Precipitation by month
Siwan climate table
| Month | High °C°F | Low °C°F | Mean °C°F | Precip. mmin |
|---|---|---|---|---|
| Jan | 2373 | 846 | 1560 | 110.4 |
| Feb | 2882 | 1253 | 2068 | 140.6 |
| Mar | 3594 | 1763 | 2679 | 100.4 |
| Apr | 40104 | 2475 | 3290 | 160.6 |
| May | 42107 | 2882 | 3594 | 522.0 |
| Jun | 40103 | 2985 | 3594 | 1556.1 |
| Jul | 3493 | 2780 | 3087 | 29011 |
| Aug | 3290 | 2679 | 2985 | 2349.2 |
| Sep | 3188 | 2476 | 2882 | 1797.1 |
| Oct | 3187 | 2068 | 2578 | 461.8 |
| Nov | 2781 | 1458 | 2169 | 10.0 |
| Dec | 2374 | 949 | 1661 | 30.1 |
| Year | 42107 | 846 | 2679 | 1,01240 |
“Year” row: highest monthly high, lowest monthly low, annual mean and annual total.
| Month | Humid. | Cloud | Solar | Daylight |
|---|---|---|---|---|
| Jan | 50% | 38% | 2.9 | 10:40 |
| Feb | 43% | 27% | 4.3 | 11:14 |
| Mar | 31% | 25% | 5.7 | 11:56 |
| Apr | 25% | 33% | 6.4 | 12:45 |
| May | 33% | 42% | 6.4 | 13:25 |
| Jun | 49% | 62% | 5.5 | 13:46 |
| Jul | 77% | 80% | 4.6 | 13:38 |
| Aug | 83% | 76% | 4.9 | 13:03 |
| Sep | 84% | 61% | 4.6 | 12:16 |
| Oct | 73% | 24% | 4.5 | 11:29 |
| Nov | 62% | 15% | 3.7 | 10:49 |
| Dec | 56% | 29% | 2.8 | 10:30 |
Humid. = average relative humidity at 2 m; cloud = average cloud amount; solar = average daily solar energy reaching the ground in kWh/m² (all-sky); daylight in hours:minutes, calculated for the 15th of each month.
What the climate of Siwan is like
The warmest month is May, with an average high of 42 °C107 °F and a low of 28 °C82 °F. The coldest is January, when highs average 23 °C73 °F and lows 8 °C46 °F. Seasons are strongly marked: the warmest month is on average 19.4 °C34.8 °F warmer than the coldest.
It is wet, with about 1,012 mm40 in of precipitation per year. The wettest three-month stretch is July–September, which brings 70% of the annual total. Months with less than 20 mm0.8 in on average: November–April. The wettest month is July (290 mm11 in), the driest is November (1 mm0.0 in).
Relative humidity ranges from 25% in April to 84% in September. The clearest skies (lowest average cloud amount, 15%) are typical of November. Average wind speed near the ground ranges from 4 km/h (3 mph) in November to 10 km/h (6 mph) in June. Daylight lasts from about 10.5 hours in December to 13.8 hours in June.
Best time to visit Siwan
Based on these averages, the most comfortable months for sightseeing and outdoor activities are November–February: average highs of 23 °C73 °F to 28 °C82 °F with 1 mm0.0 in to 14 mm0.6 in of precipitation per month.
The most challenging month is July, which is hot, with average highs of 34 °C93 °F, very wet (290 mm11 in) and humid (77% relative humidity).
Comfort score: months are ranked by how close they come to an average high of 21–28 °C (70–82 °F), lows above 5 °C (41 °F), little precipitation and moderate humidity. The best-ranked months of each place are recommended, even where none meets all of these. These are general rules of thumb applied to long-term averages.
What to pack for Siwan
- Winter (December–February) — highs 2373 to 28 °C82 °F, lows 846 to 12 °C53 °F, about 9 mm0.4 in of precipitation a month. Pack light summer clothes such as T-shirts, shorts or light dresses and an extra layer for the cooler mornings and evenings.
- Spring (March–May) — highs 3594 to 42 °C107 °F, lows 1763 to 28 °C82 °F, about 26 mm1.0 in of precipitation a month. Pack very light, breathable clothing, a sun hat and plenty of water.
- Summer (June–August) — highs 3290 to 40 °C103 °F, lows 2679 to 29 °C85 °F, about 226 mm8.9 in of precipitation a month. Pack very light, breathable clothing, a sun hat and plenty of water and a good rain jacket or umbrella and quick-drying shoes.
- Autumn (September–November) — highs 2781 to 31 °C88 °F, lows 1458 to 24 °C76 °F, about 75 mm3.0 in of precipitation a month. Pack light summer clothes such as T-shirts, shorts or light dresses.
How Siwan compares
Compared with Chapra, about 63 km to the southeast, Siwan has practically the same average temperature and receives a similar amount of precipitation.
Of the 382 places in India covered by World Climates, Siwan is the 203rd warmest by annual mean temperature and the 177th wettest by annual precipitation. See all of them on the India climate page.
Places in other countries with the most similar temperature and rainfall pattern: Janakpur (Nepal, Cwa), Birgañj (Nepal, Cwa) and Lahan (Nepal, Cwa).
Nearby places
- Chapra 63 km · 26 °C79 °F · 1,041 mm41 in
- Bettiah 66 km · 26 °C78 °F · 1,239 mm49 in
- Mothihari 73 km · 26 °C78 °F · 1,134 mm45 in
- Kushinagar 74 km · 26 °C79 °F · 1,084 mm43 in
- Arrah 80 km · 26 °C79 °F · 968 mm38 in
- Mau 85 km · 26 °C79 °F · 952 mm37 in
- Bagaha 101 km · 26 °C78 °F · 1,239 mm49 in
- Birgañj 103 km · 26 °C79 °F · 1,219 mm48 in
Frequently asked questions
What is the warmest month in Siwan?
May is the warmest month in Siwan, with an average high of 42 °C (107 °F) and an average low of 28 °C (82 °F).
What is the coldest month in Siwan?
January is the coldest month, with an average high of 23 °C (73 °F) and an average low of 8 °C (46 °F).
When does it rain the most in Siwan?
July is the wettest month with about 290 mm (11.4 in) of precipitation; November is the driest with about 1 mm (0.0 in).
What is the best time to visit Siwan?
Judging by long-term averages, the most comfortable months are November–February.
About this data
All figures are 25-year averages (January 2001 – December 2025) from the NASA POWER project. Temperature, humidity, wind and precipitation come from the MERRA-2 reanalysis (precipitation is the bias-corrected MERRA-2 product), cloud and solar values from CERES satellite data. They describe a grid cell of roughly 50–70 km, not a single weather station, so they can differ from airport records — most of all on coasts, in mountains and for rainfall. Average highs and lows are the monthly mean temperature plus/minus half of the average daily temperature range. Counts of rainy days are not part of this dataset.