Climate and average weather in Sơn La
In Sơn La, the summers are humid, hot, wet, and mostly cloudy and the winters are mild and partly cloudy.
Over the course of the year, the temperature in Sơn La typically varies from 12°C to 30°C, and is rarely below 6°C or above 34°C. May is the hottest month of the year, while January is the coldest.
Based on the travel score, the best time of year to visit Sơn La for warm-weather activities is from mid October to late March.
- Hottest
- May
- 30°
- Coldest
- Jan
- 12°
- Wettest
- Jul
- 288 mm
- Driest
- Feb
- 19 mm
- Rain / yr
- 1340 mm
- 154 wet days
- Daylight
- 10.7–13.3 h
- shortest–longest
- Elevation
- 608 m
- 21.3°N
- Clearest
- Mar
- 50% cloud
Sơn La is the old provincial capital of Son La province, Vietnam.
- Density
- 328/km²
- people per km²
Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.
Sơn La weather by month, at a glance
The whole year in one picture — sky, rain, humidity, temperature and travel score. Click any band to jump to its full chart.
Each stripe is one measure across the whole year, stacked so a single day reads top to bottom. The sky band runs overcast grey on top down to clear blue at the base — more blue means sunnier — followed by the rainfall curve, the humidity band, a temperature strip that tints each stretch of the year by how warm its average high is, and the travel-score line at the foot. Scan straight down any date to read that day across every measure at once; the score climbs highest around mid October to late March.
Temperature through the year
Daily average highs and lows in Sơn La, from 1991–2020 of climate data. The shaded bands show the range most days fall in — 10th to 90th percentile.
The hot season lasts 6.0 months, from April 4 to October 4, with daily high temperatures above 28°C. The hottest month of the year in Sơn La is May, with an average high of 30°C and low of 22°C.
The cool season lasts 2.3 months, from December 2 to February 9, with daily high temperatures below 23°C. The coldest month of the year in Sơn La is January, with an average low of 12°C and high of 21°C.
Days typically run about 9°C warmer than nights, with the widest day–night swing (around 11°C) in March.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | 21 | 23 | 27 | 29 | 30 | 30 | 29 | 29 | 29 | 27 | 25 | 22 |
| Avg low (°C) | 12 | 13 | 16 | 19 | 22 | 23 | 23 | 22 | 21 | 19 | 16 | 12 |
| Avg high (°C) | Avg low (°C) | |
|---|---|---|
| Jan | 21 | 12 |
| Feb | 23 | 13 |
| Mar | 27 | 16 |
| Apr | 29 | 19 |
| May | 30 | 22 |
| Jun | 30 | 23 |
| Jul | 29 | 23 |
| Aug | 29 | 22 |
| Sep | 29 | 21 |
| Oct | 27 | 19 |
| Nov | 25 | 16 |
| Dec | 22 | 12 |
How hot and cold Sơn La really feels
The felt-temperature range through the year — heat index on the day's high (summer humidity), wind chill on the night's low (winter wind). The dashed lines are the plain thermometer; the gap is how much hotter or colder it really feels.
On the hottest afternoons, once humidity is folded in, Sơn La feels like about 34°C (around June 5). About 123 days a year carry some heat stress, peaking in June.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Feels-like high (°C) | 21 | 23 | 27 | 30 | 33 | 33 | 33 | 32 | 31 | 28 | 25 | 22 |
| Air high (°C) | 21 | 23 | 27 | 29 | 30 | 30 | 29 | 29 | 29 | 27 | 25 | 22 |
| Feels-like low (°C) | 12 | 13 | 16 | 19 | 22 | 23 | 23 | 22 | 21 | 19 | 16 | 12 |
| Air low (°C) | 12 | 13 | 16 | 19 | 22 | 23 | 23 | 22 | 21 | 19 | 16 | 12 |
| Feels-like high (°C) | Air high (°C) | Feels-like low (°C) | Air low (°C) | |
|---|---|---|---|---|
| Jan | 21 | 21 | 12 | 12 |
| Feb | 23 | 23 | 13 | 13 |
| Mar | 27 | 27 | 16 | 16 |
| Apr | 30 | 29 | 19 | 19 |
| May | 33 | 30 | 22 | 22 |
| Jun | 33 | 30 | 23 | 23 |
| Jul | 33 | 29 | 23 | 23 |
| Aug | 32 | 29 | 22 | 22 |
| Sep | 31 | 29 | 21 | 21 |
| Oct | 28 | 27 | 19 | 19 |
| Nov | 25 | 25 | 16 | 16 |
| Dec | 22 | 22 | 12 | 12 |
Average hourly temperature in Sơn La
A compact picture of the whole year, hour by hour: each column is a day, each row an hour, and the color is the modeled average temperature. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
Read left to right for the day of the year and top to bottom for the hour of the day; the color is the modeled temperature, cool blues through to hot reds on the same scale as the other charts. A vertical slice is a single day's swing — coolest just before dawn, warmest in the mid-afternoon — while a horizontal slice follows one hour across the seasons. The darker overlay marks night and the lighter one the twilight around sunrise and sunset. Colors run warmest on May afternoons, near 30°C, and coldest before dawn in January, near 12°C.
Sơn La weather by month
Every month at a glance. Click a month for its detailed page.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|
| Jan | 21° / 12° | 24 | 4 | 10.8 | 7.3 |
| Feb | 23° / 13° | 19 | 3.6 | 11.3 | 7.9 |
| Mar | 27° / 16° | 50 | 7.1 | 11.8 | 7.1 |
| Apr | 29° / 19° | 72 | 12.8 | 12.5 | 5.2 |
| May | 30° / 22° | 147 | 19.3 | 13 | 3.7 |
| Jun | 30° / 23° | 209 | 23 | 13.3 | 3.2 |
| Jul | 29° / 23° | 288 | 24.5 | 13.2 | 3.4 |
| Aug | 29° / 22° | 283 | 25.3 | 12.7 | 3.4 |
| Sep | 29° / 21° | 150 | 17.5 | 12.1 | 4.4 |
| Oct | 27° / 19° | 49 | 8.3 | 11.5 | 6.6 |
| Nov | 25° / 16° | 27 | 4.5 | 11 | 7.8 |
| Dec | 22° / 12° | 23 | 3.6 | 10.7 | 7.6 |
Chance of rain
How likely it is to rain on a typical day, and how that shifts across the wetter and drier seasons.
Sơn La gets about 1340 mm of precipitation a year. On a typical day the chance of rain is often wet, but that rises and falls sharply with the seasons.
The wetter season lasts 5.4 months, from around Apr 17 to Sep 28, peaking in August at about 84% chance on a given day. The drier stretch runs the rest of the year, bottoming out around Dec 19.
July is the wettest month by volume, with 288 mm over about 25 wet days; February is the driest, with 19 mm.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rain on a day (%) | 13 | 13 | 23 | 42 | 62 | 77 | 80 | 80 | 59 | 27 | 15 | 12 |
| Rain days | 4 | 4 | 7 | 13 | 19 | 23 | 25 | 25 | 18 | 8 | 5 | 4 |
| Rain on a day (%) | Rain days | |
|---|---|---|
| Jan | 13 | 4 |
| Feb | 13 | 4 |
| Mar | 23 | 7 |
| Apr | 42 | 13 |
| May | 62 | 19 |
| Jun | 77 | 23 |
| Jul | 80 | 25 |
| Aug | 80 | 25 |
| Sep | 59 | 18 |
| Oct | 27 | 8 |
| Nov | 15 | 5 |
| Dec | 12 | 4 |
Monthly rainfall
Over a full year, Sơn La collects about 1340 mm of rain across 154 wet days — roughly 112 mm in an average month.
It doesn’t fall evenly. July is the wettest month with 288 mm, while February is the driest at just 19 mm. The three wettest months alone bring about 58% of the year’s total.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rainfall (mm) | 24 | 19 | 50 | 72 | 147 | 209 | 288 | 283 | 150 | 49 | 27 | 23 |
| Rain days | 4 | 4 | 7 | 13 | 19 | 23 | 25 | 25 | 18 | 8 | 5 | 4 |
| Rainfall (mm) | Rain days | |
|---|---|---|
| Jan | 24 | 4 |
| Feb | 19 | 4 |
| Mar | 50 | 7 |
| Apr | 72 | 13 |
| May | 147 | 19 |
| Jun | 209 | 23 |
| Jul | 288 | 25 |
| Aug | 283 | 25 |
| Sep | 150 | 18 |
| Oct | 49 | 8 |
| Nov | 27 | 5 |
| Dec | 23 | 4 |
Clouds and sunshine
How often the daytime sky is clear, partly cloudy or overcast.
In Sơn La, the average share of the sky covered by clouds shows significant seasonal variation over the course of the year.
The clearer part of the year begins around September 25 and lasts for 7.5 months, ending around May 11. The clearest month is March, when the sky is clear, mostly clear, or partly cloudy 61% of the time on average.
The cloudier part of the year begins around May 12 and lasts for 4.5 months, ending around September 24. The cloudiest month is June, when it is overcast or mostly cloudy 92% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clearer (%) | 47 | 58 | 61 | 56 | 31 | 8 | 9 | 16 | 31 | 50 | 54 | 51 |
| Cloudier (%) | 53 | 42 | 39 | 44 | 69 | 92 | 91 | 84 | 69 | 50 | 46 | 49 |
| Clearer (%) | Cloudier (%) | |
|---|---|---|
| Jan | 47 | 53 |
| Feb | 58 | 42 |
| Mar | 61 | 39 |
| Apr | 56 | 44 |
| May | 31 | 69 |
| Jun | 8 | 92 |
| Jul | 9 | 91 |
| Aug | 16 | 84 |
| Sep | 31 | 69 |
| Oct | 50 | 50 |
| Nov | 54 | 46 |
| Dec | 51 | 49 |
Daylight, sunrise and sunset
Hours of daylight through the year, with sunrise and sunset times.
The gold band is daylight — sunrise runs along its lower edge, sunset along the upper — so it widens toward summer and pinches toward winter, with night the dark area above and below. The longest day, around June 8, brings about 13 h 18 min of light; the shortest, around January 1, only 10 h 42 min — a swing of roughly 2 h 36 min.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight (h) | 10.8 | 11.3 | 11.8 | 12.5 | 13.0 | 13.3 | 13.2 | 12.7 | 12.1 | 11.5 | 11.0 | 10.7 |
| Sunrise (AM) | 6:49 | 6:41 | 6:19 | 5:50 | 5:30 | 5:26 | 5:34 | 5:46 | 5:55 | 6:04 | 6:21 | 6:39 |
| Sunset (PM) | 5:39 | 5:57 | 6:09 | 6:19 | 6:31 | 6:43 | 6:45 | 6:31 | 6:02 | 5:34 | 5:19 | 5:22 |
| Daylight (h) | Sunrise (AM) | Sunset (PM) | |
|---|---|---|---|
| Jan | 10.8 | 6:49 | 5:39 |
| Feb | 11.3 | 6:41 | 5:57 |
| Mar | 11.8 | 6:19 | 6:09 |
| Apr | 12.5 | 5:50 | 6:19 |
| May | 13.0 | 5:30 | 6:31 |
| Jun | 13.3 | 5:26 | 6:43 |
| Jul | 13.2 | 5:34 | 6:45 |
| Aug | 12.7 | 5:46 | 6:31 |
| Sep | 12.1 | 5:55 | 6:02 |
| Oct | 11.5 | 6:04 | 5:34 |
| Nov | 11.0 | 6:21 | 5:19 |
| Dec | 10.7 | 6:39 | 5:22 |
Sunny days
How many genuinely sunny days each month brings — days the sky stays clear or mostly clear — banded into plain-language zones.
Sơn La averages about 7 sunny days a month — counting the days the sky stays clear or mostly clear — with a clear seasonal swing between 1 and 13 days.
The sunnier stretch runs 7.3 months, from around Sep 27 to May 7. The sunniest month is March, with roughly 12 sunny days (mixed).
The greyest month is June, down near 1 sunny days — about 92% fewer than the March peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sunny days | 10 | 11 | 13 | 10 | 5 | 1 | 1 | 2 | 5 | 8 | 10 | 11 |
| Sky | Mixed | Mixed | Mixed | Mixed | Gloomy | Gloomy | Gloomy | Gloomy | Gloomy | Mixed | Mixed | Mixed |
| Sunny days | Sky | |
|---|---|---|
| Jan | 10 | Mixed |
| Feb | 11 | Mixed |
| Mar | 13 | Mixed |
| Apr | 10 | Mixed |
| May | 5 | Gloomy |
| Jun | 1 | Gloomy |
| Jul | 1 | Gloomy |
| Aug | 2 | Gloomy |
| Sep | 5 | Gloomy |
| Oct | 8 | Mixed |
| Nov | 10 | Mixed |
| Dec | 11 | Mixed |
Humidity comfort
Share of days at each humidity comfort level, based on the dew point — the measure that tracks how muggy it actually feels.
Humidity comfort is graded by the dew point — the temperature at which the air would be fully saturated — because it tracks how muggy it actually feels far better than relative humidity does. A low dew point feels dry and crisp; a high one feels sticky and oppressive no matter the reading on a humidity gauge.
In Sơn La, how humid it feels changes dramatically over the year.
The more humid part of the year lasts 7.2 months, from around March 24 to October 29. The muggiest month is June, when the air feels humid, muggy or worse about 100% of the time.
The most comfortable stretch runs from around October 30 to March 23, and January is the most comfortable month — the air is dry or comfortable 93% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry (%) | 59 | 47 | 19 | 2 | 0 | 0 | 0 | 0 | 0 | 4 | 23 | 53 |
| Comfortable (%) | 34 | 35 | 26 | 10 | 2 | 0 | 0 | 0 | 1 | 9 | 31 | 34 |
| Humid (%) | 7 | 16 | 39 | 28 | 8 | 1 | 0 | 0 | 6 | 25 | 30 | 11 |
| Muggy (%) | 0 | 1 | 15 | 50 | 40 | 7 | 2 | 3 | 30 | 47 | 16 | 1 |
| Oppressive (%) | 0 | 0 | 0 | 9 | 50 | 92 | 97 | 97 | 63 | 15 | 1 | 0 |
| Miserable (%) | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| Dry (%) | Comfortable (%) | Humid (%) | Muggy (%) | Oppressive (%) | Miserable (%) | |
|---|---|---|---|---|---|---|
| Jan | 59 | 34 | 7 | 0 | 0 | 0 |
| Feb | 47 | 35 | 16 | 1 | 0 | 0 |
| Mar | 19 | 26 | 39 | 15 | 0 | 0 |
| Apr | 2 | 10 | 28 | 50 | 9 | 0 |
| May | 0 | 2 | 8 | 40 | 50 | 0 |
| Jun | 0 | 0 | 1 | 7 | 92 | 0 |
| Jul | 0 | 0 | 0 | 2 | 97 | 1 |
| Aug | 0 | 0 | 0 | 3 | 97 | 0 |
| Sep | 0 | 1 | 6 | 30 | 63 | 0 |
| Oct | 4 | 9 | 25 | 47 | 15 | 0 |
| Nov | 23 | 31 | 30 | 16 | 1 | 0 |
| Dec | 53 | 34 | 11 | 1 | 0 | 0 |
Wind
Average wind speed through the year, banded into plain-language speed zones so a number reads as 'breezy' or 'calm' without knowing the scale.
This is the average sustained wind speed at the standard 10 metres above open ground — the steady flow a weather station reports, not the sharper gusts that come and go, which can run half again as fast. It's the number that says whether a place is generally breezy or calm.
Wind in Sơn La is steady company: average speeds sit near 5 km/h — calm — in every month of the year, with no meaningful windy or calm season.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wind speed (km/h) | 6 | 6 | 6 | 5 | 5 | 4 | 4 | 4 | 4 | 5 | 5 | 6 |
| Feels | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm |
| Wind speed (km/h) | Feels | |
|---|---|---|
| Jan | 6 | calm |
| Feb | 6 | calm |
| Mar | 6 | calm |
| Apr | 5 | calm |
| May | 5 | calm |
| Jun | 4 | calm |
| Jul | 4 | calm |
| Aug | 4 | calm |
| Sep | 4 | calm |
| Oct | 5 | calm |
| Nov | 5 | calm |
| Dec | 6 | calm |
Hazard calendar for Sơn La
When the seasonal hazards worth planning around — the rainy season, tropical-cyclone risk and dust haze — are active through the year.
Sơn La's monsoon runs May–September, when most of the year's rain falls.
Best time to visit Sơn La
To characterize how pleasant the weather is in Sơn La throughout the year, we compute two travel scores — one for general sightseeing, one for beach and pool weather.
Around late October, Sơn La is still near the start of its best-weather window — great conditions with the peak-season crowds not yet at full swing.
Inferred from the travel-score curve; month-by-month visitor numbers are a planned addition.
The travel score favors clear, rainless days with daytime highs between 18°C and 28°C. Based on this score, the best time of year to visit Sơn La for general outdoor tourist activities is from mid October to late March, with a peak score in the third week of February.
The travel score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Travel score (0–10) | 7.3 | 7.8 | 7.1 | 5.2 | 3.7 | 3.2 | 3.4 | 3.4 | 4.5 | 6.6 | 7.7 | 7.6 |
| Rating | good | ideal | good | fair | fair | poor | poor | poor | fair | good | ideal | ideal |
| Travel score (0–10) | Rating | |
|---|---|---|
| Jan | 7.3 | good |
| Feb | 7.8 | ideal |
| Mar | 7.1 | good |
| Apr | 5.2 | fair |
| May | 3.7 | fair |
| Jun | 3.2 | poor |
| Jul | 3.4 | poor |
| Aug | 3.4 | poor |
| Sep | 4.5 | fair |
| Oct | 6.6 | good |
| Nov | 7.7 | ideal |
| Dec | 7.6 | ideal |
The beach/pool score favors clear, rainless days with daytime highs between 24°C and 34°C. Based on this score, the best times of year to visit Sơn La for hot-weather activities run from mid February to early May and again from late September to late November, with a peak score in the second week of March.
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
What to pack for Sơn La, by month
Month by month, what's worth putting in the bag — from the temperature range, rain chance, sun and wind. Tap a month for a quick packing note.
For a warm-season trip around May (highs near 30°C), the essentials are light clothes, rain gear and sun protection. In the cold season around January (highs near 21°C), pack a light layer.
In May, Sơn La sees daytime highs around 30°C and nights near 22°C. Pack light clothes and rain gear. Worth having: sun protection. About 19 days see rain.
UV index (midday) in Sơn La by month
Clear-sky midday UV index through the year, shaded by the WHO exposure levels — how much sun protection each month calls for.
Under clear skies, the midday UV index in Sơn La peaks around June 20 at about 13 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 18 at about 6 (high).
The index reaches 3 or more — the level where the WHO recommends sun protection — every month of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 7 | 9 | 11 | 9 | 11 | 14 | 13 | 13 | 9 | 9 | 8 | 6 |
| Level | Very high | Very high | Extreme | Very high | Extreme | Extreme | Extreme | Extreme | Very high | Very high | Very high | High |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 7 | Very high |
| Feb | 9 | Very high |
| Mar | 11 | Extreme |
| Apr | 9 | Very high |
| May | 11 | Extreme |
| Jun | 14 | Extreme |
| Jul | 13 | Extreme |
| Aug | 13 | Extreme |
| Sep | 9 | Very high |
| Oct | 9 | Very high |
| Nov | 8 | Very high |
| Dec | 6 | High |
Average hourly UV index in Sơn La
Modeled clear-sky UV for every hour of every day — when in the day sun protection actually matters.
The whole year hour by hour: each column is a day, each row an hour, and the color is the modeled clear-sky UV index — the midday peak scaled down as the sun sits lower in the sky. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
UV falls off far faster than brightness as the sun drops, so even in June the burn window is concentrated in the middle of the day: about 9 hours a day reach index 3 (protection recommended), and 7 hours reach 6 or more. Mornings and late afternoons stay comparatively gentle year round.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV ≥ 3 (h/day) | 6 | 6.5 | 7.5 | 7.5 | 8 | 9 | 8.5 | 8.5 | 7.5 | 7 | 6 | 5.5 |
| UV ≥ 6 (h/day) | 3 | 4.5 | 5.5 | 5 | 6 | 7 | 6.5 | 6.5 | 5 | 4.5 | 3.5 | 1.5 |
| UV ≥ 3 (h/day) | UV ≥ 6 (h/day) | |
|---|---|---|
| Jan | 6 | 3 |
| Feb | 6.5 | 4.5 |
| Mar | 7.5 | 5.5 |
| Apr | 7.5 | 5 |
| May | 8 | 6 |
| Jun | 9 | 7 |
| Jul | 8.5 | 6.5 |
| Aug | 8.5 | 6.5 |
| Sep | 7.5 | 5 |
| Oct | 7 | 4.5 |
| Nov | 6 | 3.5 |
| Dec | 5.5 | 1.5 |
Air quality in Sơn La by month
Average fine-particle pollution (PM2.5) through the year — so you can see which months the air is worst, not just the yearly average.
Air quality in Sơn La is worst in April — around 151 µg/m³ PM2.5 (very unhealthy), about 12.9× the cleanest month (August, 12 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 32 | 38 | 67 | 151 | 58 | 14 | 12 | 12 | 16 | 23 | 26 | 31 |
| Level | Moderate | Poor | Unhealthy | Very unhealthy | Unhealthy | Moderate | Good | Good | Moderate | Moderate | Moderate | Moderate |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 32 | Moderate |
| Feb | 38 | Poor |
| Mar | 67 | Unhealthy |
| Apr | 151 | Very unhealthy |
| May | 58 | Unhealthy |
| Jun | 14 | Moderate |
| Jul | 12 | Good |
| Aug | 12 | Good |
| Sep | 16 | Moderate |
| Oct | 23 | Moderate |
| Nov | 26 | Moderate |
| Dec | 31 | Moderate |
Growing season
Sơn La is frost-free year round — even the coldest nights rarely reach freezing, so there is no start or end to the growing season.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frost-free chance (%) | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 |
| Frost nights | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Frost-free chance (%) | Frost nights | |
|---|---|---|
| Jan | 100 | 0 |
| Feb | 100 | 0 |
| Mar | 100 | 0 |
| Apr | 100 | 0 |
| May | 100 | 0 |
| Jun | 100 | 0 |
| Jul | 100 | 0 |
| Aug | 100 | 0 |
| Sep | 100 | 0 |
| Oct | 100 | 0 |
| Nov | 100 | 0 |
| Dec | 100 | 0 |
Growing degree days
Growing degree days tally heat above 10°C: each day adds however many degrees its average temperature runs over that threshold, and cold days add nothing. Sơn La banks about 4,548 degree days a year, and the running total — which growers use to time plantings and predict maturity — climbs fastest around June.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Growing degree days (°C·days) | 196 | 230 | 354 | 425 | 495 | 491 | 494 | 488 | 453 | 405 | 304 | 213 |
| Growing degree days (°C·days) | |
|---|---|
| Jan | 196 |
| Feb | 230 |
| Mar | 354 |
| Apr | 425 |
| May | 495 |
| Jun | 491 |
| Jul | 494 |
| Aug | 488 |
| Sep | 453 |
| Oct | 405 |
| Nov | 304 |
| Dec | 213 |
Solar energy
Average daily shortwave solar energy reaching the ground, banded into brightness zones so the number means something at a glance.
Solar energy is how much sunlight actually reaches the ground each day, measured in kilowatt-hours per square metre (kWh/m²) — the combined effect of how long the sun is up, how high it climbs, and how much cloud gets in the way. It's the raw fuel a solar panel has to work with: for scale, 1 kWh/m² a day is dim and wintry, while 7+ is desert-bright.
Sơn La receives about 4.2 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 3.1 and 5.4 kWh/m².
The brighter stretch of the year lasts 7.3 months, from around Feb 24 to Oct 2. The brightest month is April, averaging about 5.2 kWh/m² (bright).
The dimmest month is December, down near 3.2 kWh/m² — roughly 39% less than the April peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar energy (kWh/m²) | 3.1 | 3.9 | 4.8 | 5.3 | 5.1 | 4.6 | 4.4 | 4.4 | 4.4 | 3.9 | 3.5 | 3.2 |
| Level | Moderate | Moderate | Bright | Bright | Bright | Bright | Bright | Bright | Bright | Moderate | Moderate | Moderate |
| Solar energy (kWh/m²) | Level | |
|---|---|---|
| Jan | 3.1 | Moderate |
| Feb | 3.9 | Moderate |
| Mar | 4.8 | Bright |
| Apr | 5.3 | Bright |
| May | 5.1 | Bright |
| Jun | 4.6 | Bright |
| Jul | 4.4 | Bright |
| Aug | 4.4 | Bright |
| Sep | 4.4 | Bright |
| Oct | 3.9 | Moderate |
| Nov | 3.5 | Moderate |
| Dec | 3.2 | Moderate |
Where is Sơn La?
Sơn La sits at 21.3°N, 103.9°E, 608 m above sea level, in Vietnam. The nearest listed city is Ít Ong, 24 km away.
Topography around Sơn La
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Sơn La.
Within 3 km, the terrain around Sơn La has significant variations in elevation — a maximum elevation change of 348 m around an average of 674 m above sea level; within 16 km, very significant variations in elevation — a maximum elevation change of 1,404 m; within 80 km, extreme variations in elevation — a maximum elevation change of 2,830 m.
The land around Sơn La is covered by trees (59%) within 3 km, trees (69%) and grassland (21%) within 16 km, and trees (68%) and grassland (27%) within 80 km.
Vietnam travel facts
- Travel advisory
- Level 1
- Exercise Normal Precautions
- Power plugs
- Type A / B / C / F
- 220 V · 50 Hz
- Prices
- ≈ 29% of US
- price level, 2025
- GDP per capita
- $5,066
- 2025
- Happiness
- 6.4 / 10
- World Happiness, 2025
- Safe drinking water
- 59%
- of population, 2024
- Homicide rate
- 1.5
- per 100k, 2011
- Road deaths
- 30.6
- per 100k/yr, 2019
- Income group
- Upper middle
- World Bank
- English
- Moderate
- EF EPI 500
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Sơn La (21.3256°, 103.9188°, elevation 608 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).