Vientiane weather by month — averages, rainfall & climate trends
Capital of Laos since the days of the Lan Xang kingdom, Vientiane spreads along the banks of the Mekong, where the golden stupa of Pha That Luang has watched the monsoon arrive for centuries. Average temperatures and rainfall by month, a climate graph, today's conditions versus the long-term average, and how the climate has shifted since 1940 — all on one page for Vientiane, Laos.
Today vs average
−3.5°Cmuch cooler than usual
How it’s changed
Right now
What it's doing today vs the historical average for this date.
Right now
25.8°
28°24°31°24°
32°25°30°25°
30°25°31°25°33°25°On this date — July 20
Cooler than usual · 3.5°C below the average high
- Record high: 35.6° · 1998
- Record low: 23.0° · 1985
- One year ago: 33.3°
Every July 20 in history — coldest to hottest
Dots show daily highs (top) and lows (bottom) for each July 20 on record (n = 87). Outlined dots are today's forecast.
Area we sample
Each city's history comes from one ERA5 grid cell — about 28 km across, shown by the dashed box. Near mountains or coasts, conditions can vary across the cell.
Location & data
Historical weather for Vientiane is sampled from the ECMWF ERA5 reanalysis at 17.97°N, 102.60°E, with daily records since 1940.
- Coordinates
- 17.97°N, 102.60°E
- Time zone
- Asia/Vientiane
- Period
- 1940–2026
- Data source
- ERA5 (ECMWF)
Last 30 days
20 of the last 31 days were warmer than the historical average for that date. Average difference: +0.5°C.
Each bar is one day, from morning low to afternoon high. Warm-colored bars are days whose mean ran above average; cool bars ran below. The dot inside the bar is the daily mean. The shaded band is the typical 10–90% range expected for that date. Average = the day's mean temperature averaged across every year of record (1940–2026) for that calendar date.
This date over the years
One dot per year — the mean temperature on this calendar date. Dots are warmer or cooler than the long-term average (dashed line); the shaded band is the typical 10–90% range, and the highlighted dot is today's forecast. Based on ERA5 reanalysis — modelled estimates, not station readings.
Weather by month
Average temperatures and rainfall for each month — what a typical year looks like, from the full record.Climate overview
Vientiane occupies the low-lying Vientiane Plain beside the Mekong, with Thailand just across the river. Its climate is tropical and driven by the monsoon: rain falls mainly between May and October, the months from November through February are dry and relatively cool, and March and April bring dry heat. Across the country the monsoon breaks at roughly the same time, though its onset shifts from one year to the next.
Flooding comes mostly between August and November, when storms spinning out of the South China Sea swell the Mekong, and Lao floods tend to rise and fall quickly, fed by heavy rain over the mountains. The flood of 1966 is still remembered among the country's worst, and in 1995 a large share of the Vientiane Plain sat under water for weeks. Dry years cut the other way, with rainfall sometimes falling well short of what rice cultivation needs, and climate-driven drought, compounded by dams upstream, is now straining the river itself.
The warmest month is April, with a daily mean around 28.8°C and typical afternoon highs of 34.6°C. At the other extreme, January averages 22.1°C, with typical overnight lows of 16.2°C.
Vientiane picks up roughly 1996 mm a year, with a peak of 397 mm in August and as little as 6 mm in December.
Over the full record (since 1940), the annual mean temperature in Vientiane has risen by 1.8°C between its first decade and its last. Days above 30°C have grown noticeably more frequent — from around 205 a year in the first decade to about 300 in the last.
Climate graph (climograph)
April is the warmest month, January the coolest — a yearly swing of 7°C. Wettest month: August (~397 mm). Whole year averages ~1996 mm of rain.
Bars = average monthly rainfall (right axis). Lines = average daily high and low (left axis). Average = each month's value averaged across every year of record (1940–2026).
Monthly wind
Average daily peak wind at 10 m, by month.
Monthly solar energy
Average daily incoming solar energy in megajoules per square metre — a measured proxy for how sunny the month is.
Vientiane month by month — what to expect
Typical conditions for each month, averaged across the full record (since 1940). Daylight is the time from sunrise to sunset. Record high/low are the most extreme values in the ERA5 dataset (modelled since 1940), so they can differ from official weather-station readings.
| Month | Avg high | Avg low | Rain | Daylight | Record high | Record low |
|---|---|---|---|---|---|---|
| January | 28.7° | 16.2° | 12 mm | 11.0 h | 36.7° (2005) | 4.6° (1955) |
| February | 31.2° | 18.3° | 17 mm | 11.4 h | 38.5° (1973) | 9.8° (2016) |
| March | 33.8° | 21.5° | 43 mm | 11.9 h | 41.2° (2023) | 10.7° (1986) |
| April | 34.6° | 24.1° | 93 mm | 12.4 h | 43.0° (2024) | 16.9° (2015) |
| May | 32.8° | 24.8° | 270 mm | 12.8 h | 43.0° (2023) | 19.6° (1976) |
| June | 32.1° | 25.2° | 334 mm | 13.1 h | 40.0° (2023) | 21.0° (1967) |
| July | 31.5° | 25.0° | 340 mm | 13.0 h | 39.3° (2015) | 21.9° (1984) |
| August | 31.2° | 24.8° | 397 mm | 12.6 h | 36.9° (2021) | 22.4° (1976) |
| September | 31.1° | 24.4° | 340 mm | 12.1 h | 36.7° (2018) | 20.6° (1966) |
| October | 30.8° | 23.1° | 119 mm | 11.6 h | 36.6° (2019) | 15.2° (1994) |
| November | 29.8° | 20.2° | 24 mm | 11.1 h | 36.5° (2017) | 10.1° (1983) |
| December | 28.2° | 16.6° | 6 mm | 10.9 h | 35.3° (2023) | 5.7° (1999) |
How it has changed
Year-by-year signals from 1940 to today.Climate stripes
Annual mean shifted from 1940–1949 to 2016–2025 by +1.8°C.
Each vertical stripe is one year. Color encodes how much that year's annual mean differed from the long-term average. Average = each year's annual mean compared to the average of all years (1940–2026). cooler ← → warmer
Annual mean temperature
Long-term trend: +0.22°C per decade.
One point per year — the temperature averaged across the whole year. The dashed line is the least-squares long-term trend. Based on ERA5 reanalysis — modelled estimates, not station readings.
Seasonal warming
Sep–Nov is warming fastest: +0.28°C per decade.
Each faint line is one three-month period's average per year; the bold dashed line is its long-term trend. Different parts of the year often warm at different rates. Based on ERA5 reanalysis — modelled estimates, not station readings.
Hot days vs frost days
Days ≥ 30°C per year: 206.1 early in the record → 298.0 recently. Frost days: 0 → 0.
Thin lines are raw yearly counts; thick lines are the smoothed trend that removes year-to-year noise. The hot-day threshold is auto-picked per city so the line actually moves. Average = a centered 5-year rolling average to smooth weather noise.
Yearly hot & cold extremes
All-time high in 2024, all-time low in 1955: 43.0°C / 4.6°C.
One point per year — the single hottest and coldest day recorded that year.
Annual rainfall
~1996 mm/year on average. Last decade ran −9% vs that average. Long-term trend: −4 mm per decade.
One bar per year of total rainfall. Dashed line is the long-term average. Average = the average annual rainfall across every year of record (1940–2026).
Day-by-day grid
Each tiny square is one calendar day across the full record — ~30,000 days per city. Use the mode switch above the chart: Anomaly colors each day by how far it ran from the historical average for that date (red = warmer, blue = cooler), Daily mean temp shows the absolute mean temperature for the day (useful to see seasons and heatwaves), and Precipitation shows daily rainfall (useful to spot wet/dry seasons and droughts). Average = the long-term average for that calendar date (1940–2026).