Bihar Weather Forecast & Climate Summary
Bihar sits on the Gangetic plain between the Himalaya and the Chota Nagpur plateau, and its defining weather risk isn't just local rainfall — it's the seasonal flooding of Himalaya-fed rivers like the Kosi, whose shifting course has earned it the name 'Sorrow of Bihar'. For live interactive rainfall, wind and satellite maps over Bihar, open VayuMet.
Geography & Seasonal Cycle
The Ganga runs west to east through the middle of the state, dividing it into a north Bihar plain fed by fast, sediment-heavy rivers descending from the Nepal Himalaya (Kosi, Gandak, Bagmati, Kamla) and a comparatively drier south Bihar plain extending toward the Chota Nagpur plateau fringe.
Winter (December-February) is cold with persistent fog, part of the broader Indo-Gangetic fog belt. Pre-monsoon summer (March-June) is hot, with the loo affecting south and west Bihar. The monsoon (June-September) is generally reliable given Bihar's Gangetic-plain position, but north Bihar's flood season effectively runs through the same months, driven by combined local rainfall and Himalayan snowmelt/rainfall runoff. Post-monsoon (October-November) is a short, dry transition.
Weather Systems by Season
The Kosi's high sediment load and history of shifting its channel make it one of India's most flood-prone rivers; the 2008 embankment breach near the Nepal border caused one of the most significant river-flood disasters in recent Indian history.
Depressions and lows moving along the Gangetic plain are Bihar's main monsoon rain driver, generally giving the state more reliable rainfall than the more northwesterly parts of the Indo-Gangetic belt.
Bihar shares the broader Gangetic plain's severe winter fog problem, regularly disrupting road, rail and flight schedules.
South and west Bihar experience the loo's scorching, dry heat ahead of monsoon onset.
Frequencies cited from published IMD/IITM climatology where a source is named inline; day-count figures in the table below are computed directly from the 1951–2025 IMD daily archive.
Seasonal Weather Data
The table below is a state-wide average across Bihar's 38 districts, built from IMD's real 1991-2020 gridded rainfall/temperature normals and 1951-2025 daily archives (not a forecast). North Bihar's flood-prone plain and the drier south differ from this average — use the district climatology tool linked below for any single district's own figures.
| Season | Rainfall (mm) | Rain days | Mean Max / Min (°C) | Typical Hottest / Coldest (°C) | Sky (Sunny·Partly·Overcast days) |
|---|---|---|---|---|---|
| Winter Jan–Feb | 21.1 | 5.9 | 23.7 / 11.8 | 28.2 / 9.1 | 35.5·23.5·0.0 |
| Pre-Monsoon (Summer) Mar–May | 83.1 | 18.0 | 34.7 / 21.9 | 37.5 / 15.2 | 43.9·48.1·0.0 |
| Monsoon (SW) Jun–Sep | 837.1 | 89.6 | 33.4 / 26.3 | 37.5 / 24.5 | 4.2·102.4·15.4 |
| Post-Monsoon Oct–Dec | 56.9 | 10.1 | 27.8 / 17.0 | 32.8 / 10.0 | 61.1·30.9·0.0 |
State figures are a simple average across 38 member districts (IMD Pune 1991–2020 normal; day-count and sky figures from real 1951–2025 daily archives — see District Climatology tool for any single district's own numbers, which can differ substantially from this state average).
Recorded Extremes (IMD 1951–2025 Gridded Data)
- Highest maximum temperature recorded (Jamui): 45.4°C — 19 May 1972
- Lowest minimum temperature recorded (Aurangabad): 0.3°C — 5 Jan 1955
- Highest 24-hour rainfall recorded (Samastipur): 600 mm — 4 Aug 2005
- Highest monthly rainfall recorded (Saharsa): 1664 mm — Jul 2004
Computed directly from the real IMD 1951–2025 daily gridded archive — not a forecast, and not the same as a single-station record. IMD's gridded temperature is 1°×1° (~111 km/cell) and rainfall is 0.25°×0.25° (~25 km/cell); both are spatial analyses of many station observations; a famous single-station record (e.g. a specific town's all-time hottest day) will typically read higher than the grid-cell value shown here, since one station reading isn't smoothed over a ~25–111 km box. "Place" is the nearest district to the grid cell where the extreme occurred, not necessarily the exact spot.
Notable Historical Events
- 2008 Kosi flood: A major embankment breach that displaced millions and reshaped the river's course (Kusaha, near the Nepal border, and downstream north Bihar districts, August 2008) — Government of Bihar / national disaster assessment
Risk Profile
Monsoon (Jun-Sep). North Bihar's Himalaya-fed rivers — the Kosi, Gandak and Bagmati — pose some of the most severe and recurring flood risk in India, driven partly by rainfall and snowmelt across the border in Nepal.
Pre-monsoon (Apr-Jun). South and west Bihar see recurring loo-driven heatwave conditions.
Winter (Dec-Jan). Persistent winter fog is a major transport and public-health hazard across the state.
Occasional, south Bihar. The south Bihar plateau fringe is somewhat less monsoon-reliable than the rest of the state and can see localised drought in weak-monsoon years.
Bihar Weather Highlights
- The Kosi river's tendency to shift its course dramatically, combined with a heavy Himalayan sediment load, has earned it the name 'Sorrow of Bihar' — the 2008 embankment breach was one of India's most significant river-flood disasters.
- Much of Bihar's flood risk originates outside its own borders, in Himalayan rainfall and snowmelt over Nepal, making it a genuinely transboundary hydrological problem rather than a purely local-rainfall one.
- Bihar sits within the severe Indo-Gangetic winter fog belt, a recurring transport disruption every cold season.
All 38 Districts
Click a district on the District Climatology tool or search it on the 10-day forecast page for its own normals — the grid below is the full current list (India's Local Government Directory codes, cross-checked against the latest state reorganisation).