Climate and average weather in Siena
In Siena, the summers are hot, fairly dry, and clear and the winters are cool, snowy, and partly cloudy.
Over the course of the year, the temperature in Siena typically varies from 2°C to 29°C, and is rarely below -3°C or above 34°C. August is the hottest month of the year, while January is the coldest.
Based on the travel score, the best time of year to visit Siena for warm-weather activities is from early May to late October.
- Hottest
- Aug
- 29°
- Coldest
- Jan
- 2°
- Wettest
- Nov
- 120 mm
- Driest
- Jul
- 31 mm
- Rain / yr
- 855 mm
- 107 wet days
- Daylight
- 8.8–15.2 h
- shortest–longest
- Elevation
- 322 m
- 43.3°N
- Clearest
- Jul
- 27% cloud
- Air quality
- Good
- PM10 18.4 µg/m³ · 2019
Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.
Siena 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 early May to late October.
Temperature through the year
Daily average highs and lows in Siena, from 1991–2020 of climate data. The shaded bands show the range most days fall in — 10th to 90th percentile.
The hot season lasts 3.2 months, from June 9 to September 13, with daily high temperatures above 25°C. The hottest month of the year in Siena is August, with an average high of 29°C and low of 18°C.
The cool season lasts 3.7 months, from November 17 to March 9, with daily high temperatures below 13°C. The coldest month of the year in Siena is January, with an average low of 2°C and high of 9°C.
Days typically run about 9°C warmer than nights, with the widest day–night swing (around 12°C) in July.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | 9 | 10 | 14 | 17 | 22 | 26 | 29 | 29 | 25 | 19 | 14 | 10 |
| Avg low (°C) | 2 | 2 | 4 | 7 | 11 | 15 | 17 | 18 | 14 | 10 | 6 | 3 |
| Avg high (°C) | Avg low (°C) | |
|---|---|---|
| Jan | 9 | 2 |
| Feb | 10 | 2 |
| Mar | 14 | 4 |
| Apr | 17 | 7 |
| May | 22 | 11 |
| Jun | 26 | 15 |
| Jul | 29 | 17 |
| Aug | 29 | 18 |
| Sep | 25 | 14 |
| Oct | 19 | 10 |
| Nov | 14 | 6 |
| Dec | 10 | 3 |
How hot and cold Siena 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 coldest nights, wind chill pulls the feels-like down to about -1°C (around January 27), with roughly 67 freezing days a year (feels-like at or below 0°C), worst in January.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Feels-like high (°C) | 9 | 10 | 14 | 17 | 21 | 26 | 29 | 29 | 24 | 19 | 14 | 10 |
| Air high (°C) | 9 | 10 | 14 | 17 | 22 | 26 | 29 | 29 | 25 | 19 | 14 | 10 |
| Feels-like low (°C) | -1 | -1 | 2 | 6 | 11 | 15 | 17 | 18 | 14 | 10 | 5 | 0 |
| Air low (°C) | 2 | 2 | 4 | 7 | 11 | 15 | 17 | 18 | 14 | 10 | 6 | 3 |
| Feels-like high (°C) | Air high (°C) | Feels-like low (°C) | Air low (°C) | |
|---|---|---|---|---|
| Jan | 9 | 9 | -1 | 2 |
| Feb | 10 | 10 | -1 | 2 |
| Mar | 14 | 14 | 2 | 4 |
| Apr | 17 | 17 | 6 | 7 |
| May | 21 | 22 | 11 | 11 |
| Jun | 26 | 26 | 15 | 15 |
| Jul | 29 | 29 | 17 | 17 |
| Aug | 29 | 29 | 18 | 18 |
| Sep | 24 | 25 | 14 | 14 |
| Oct | 19 | 19 | 10 | 10 |
| Nov | 14 | 14 | 5 | 6 |
| Dec | 10 | 10 | 0 | 3 |
Average hourly temperature in Siena
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 August afternoons, near 29°C, and coldest before dawn in January, near 2°C.
Siena weather by month
Every month at a glance. Click a month for its detailed page.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Snow days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|---|
| Jan | 9° / 2° | 55 | 8.1 | 0.8 | 9.2 | 1.9 |
| Feb | 10° / 2° | 65 | 8.4 | 1.2 | 10.2 | 2.5 |
| Mar | 14° / 4° | 66 | 9 | 0.5 | 11.6 | 4.2 |
| Apr | 17° / 7° | 79 | 11.3 | 0 | 13.2 | 5.4 |
| May | 22° / 11° | 71 | 10.1 | 0 | 14.5 | 6.7 |
| Jun | 26° / 15° | 50 | 7.5 | 0 | 15.1 | 7.4 |
| Jul | 29° / 17° | 31 | 5 | 0 | 14.9 | 6.5 |
| Aug | 29° / 18° | 40 | 6.2 | 0 | 13.8 | 6.3 |
| Sep | 25° / 14° | 92 | 9 | 0 | 12.3 | 7.1 |
| Oct | 19° / 10° | 109 | 10.4 | 0 | 10.8 | 6.2 |
| Nov | 14° / 6° | 120 | 11.6 | 0.1 | 9.5 | 3.8 |
| Dec | 10° / 3° | 79 | 10 | 0.5 | 8.8 | 2.1 |
Chance of rain
How likely it is to rain on a typical day, and how that shifts across the wetter and drier seasons.
Siena gets about 855 mm of precipitation a year. On a typical day the chance of rain is some rain, but that rises and falls sharply with the seasons.
The wetter season lasts 1.9 months, from around Mar 25 to May 22, peaking in April at about 40% chance on a given day. The drier stretch runs the rest of the year, bottoming out around Jul 22.
November is the wettest month by volume, with 120 mm over about 12 wet days; July is the driest, with 31 mm. Some of the cold-season precipitation falls as snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rain on a day (%) | 27 | 30 | 29 | 38 | 33 | 25 | 16 | 20 | 31 | 33 | 38 | 33 |
| Rain days | 8 | 8 | 9 | 11 | 10 | 8 | 5 | 6 | 9 | 10 | 12 | 10 |
| Rain on a day (%) | Rain days | |
|---|---|---|
| Jan | 27 | 8 |
| Feb | 30 | 8 |
| Mar | 29 | 9 |
| Apr | 38 | 11 |
| May | 33 | 10 |
| Jun | 25 | 8 |
| Jul | 16 | 5 |
| Aug | 20 | 6 |
| Sep | 31 | 9 |
| Oct | 33 | 10 |
| Nov | 38 | 12 |
| Dec | 33 | 10 |
Monthly rainfall
Over a full year, Siena collects about 855 mm of rain across 107 wet days — roughly 71 mm in an average month.
It doesn’t fall evenly. November is the wettest month with 120 mm, while July is the driest at just 31 mm. The three wettest months alone bring about 38% of the year’s total, and some of the cold-season precipitation falls as snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rainfall (mm) | 55 | 65 | 66 | 79 | 71 | 50 | 31 | 40 | 92 | 109 | 120 | 79 |
| Rain days | 8 | 8 | 9 | 11 | 10 | 8 | 5 | 6 | 9 | 10 | 12 | 10 |
| Snow days | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| Rainfall (mm) | Rain days | Snow days | |
|---|---|---|---|
| Jan | 55 | 8 | 1 |
| Feb | 65 | 8 | 1 |
| Mar | 66 | 9 | 1 |
| Apr | 79 | 11 | 0 |
| May | 71 | 10 | 0 |
| Jun | 50 | 8 | 0 |
| Jul | 31 | 5 | 0 |
| Aug | 40 | 6 | 0 |
| Sep | 92 | 9 | 0 |
| Oct | 109 | 10 | 0 |
| Nov | 120 | 12 | 0 |
| Dec | 79 | 10 | 1 |
Snow in Siena
Average snowy days through the year, the snow-season span, and estimated snowfall — for ski trips and the perennial 'will there be snow at Christmas?' question.
Siena averages about 3 snowy days a year. Snow season runs roughly Jan 12 to Mar 12 — about 2 months.
January is snowiest, with roughly 0.9 day of snow and an estimated 2 cm of snowfall. Over the year that adds up to an estimated 12 cm of snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Snow days | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| Snowfall (cm) | 2 | 4 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 4 |
| Snow days | Snowfall (cm) | |
|---|---|---|
| Jan | 1 | 2 |
| Feb | 1 | 4 |
| Mar | 1 | 2 |
| Apr | 0 | 0 |
| May | 0 | 0 |
| Jun | 0 | 0 |
| Jul | 0 | 0 |
| Aug | 0 | 0 |
| Sep | 0 | 0 |
| Oct | 0 | 0 |
| Nov | 0 | 0 |
| Dec | 1 | 4 |
Clouds and sunshine
How often the daytime sky is clear, partly cloudy or overcast.
In Siena, 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 May 21 and lasts for 4.4 months, ending around October 1. The clearest month is July, when the sky is clear, mostly clear, or partly cloudy 87% of the time on average.
The cloudier part of the year begins around October 2 and lasts for 7.6 months, ending around May 20. The cloudiest month is November, when it is overcast or mostly cloudy 58% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clearer (%) | 44 | 50 | 53 | 51 | 56 | 73 | 87 | 84 | 68 | 55 | 42 | 45 |
| Cloudier (%) | 56 | 50 | 47 | 49 | 44 | 27 | 13 | 16 | 32 | 45 | 58 | 55 |
| Clearer (%) | Cloudier (%) | |
|---|---|---|
| Jan | 44 | 56 |
| Feb | 50 | 50 |
| Mar | 53 | 47 |
| Apr | 51 | 49 |
| May | 56 | 44 |
| Jun | 73 | 27 |
| Jul | 87 | 13 |
| Aug | 84 | 16 |
| Sep | 68 | 32 |
| Oct | 55 | 45 |
| Nov | 42 | 58 |
| Dec | 45 | 55 |
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 12, brings about 15 h 12 min of light; the shortest, around January 1, only 8 h 48 min — a swing of roughly 6 h 24 min.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight (h) | 9.2 | 10.2 | 11.6 | 13.2 | 14.5 | 15.1 | 14.9 | 13.8 | 12.3 | 10.8 | 9.5 | 8.8 |
| Sunrise (AM) | 7:50 | 7:22 | 6:35 | 5:39 | 4:56 | 4:39 | 4:53 | 5:25 | 6:00 | 6:36 | 7:16 | 7:47 |
| Sunset (PM) | 4:58 | 5:36 | 6:13 | 6:51 | 7:25 | 7:51 | 7:48 | 7:13 | 6:18 | 5:23 | 4:44 | 4:35 |
| Daylight (h) | Sunrise (AM) | Sunset (PM) | |
|---|---|---|---|
| Jan | 9.2 | 7:50 | 4:58 |
| Feb | 10.2 | 7:22 | 5:36 |
| Mar | 11.6 | 6:35 | 6:13 |
| Apr | 13.2 | 5:39 | 6:51 |
| May | 14.5 | 4:56 | 7:25 |
| Jun | 15.1 | 4:39 | 7:51 |
| Jul | 14.9 | 4:53 | 7:48 |
| Aug | 13.8 | 5:25 | 7:13 |
| Sep | 12.3 | 6:00 | 6:18 |
| Oct | 10.8 | 6:36 | 5:23 |
| Nov | 9.5 | 7:16 | 4:44 |
| Dec | 8.8 | 7:47 | 4:35 |
Sunny days
How many genuinely sunny days each month brings — days the sky stays clear or mostly clear — banded into plain-language zones.
Siena averages about 13 sunny days a month — counting the days the sky stays clear or mostly clear — with a clear seasonal swing between 8 and 23 days.
The sunnier stretch runs 3.5 months, from around Jun 9 to Sep 23. The sunniest month is July, with roughly 23 sunny days (bright).
The greyest month is November, down near 8 sunny days — about 64% fewer than the July peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sunny days | 10 | 10 | 12 | 11 | 11 | 16 | 23 | 21 | 15 | 11 | 8 | 10 |
| Sky | Mixed | Mixed | Mixed | Mixed | Mixed | Bright | Bright | Bright | Mixed | Mixed | Mixed | Mixed |
| Sunny days | Sky | |
|---|---|---|
| Jan | 10 | Mixed |
| Feb | 10 | Mixed |
| Mar | 12 | Mixed |
| Apr | 11 | Mixed |
| May | 11 | Mixed |
| Jun | 16 | Bright |
| Jul | 23 | Bright |
| Aug | 21 | Bright |
| Sep | 15 | Mixed |
| Oct | 11 | Mixed |
| Nov | 8 | Mixed |
| Dec | 10 | 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 Siena, how humid it feels changes dramatically over the year.
The more humid part of the year lasts 3.9 months, from around June 5 to October 2. The muggiest month is August, when the air feels humid, muggy or worse about 61% of the time.
The most comfortable stretch runs from around October 3 to June 4, and April is the most comfortable month — the air is dry or comfortable 100% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry (%) | 100 | 100 | 100 | 98 | 75 | 27 | 14 | 10 | 36 | 67 | 93 | 100 |
| Comfortable (%) | 0 | 0 | 0 | 2 | 23 | 42 | 31 | 29 | 33 | 24 | 7 | 0 |
| Humid (%) | 0 | 0 | 0 | 0 | 2 | 27 | 42 | 42 | 26 | 9 | 1 | 0 |
| Muggy (%) | 0 | 0 | 0 | 0 | 0 | 4 | 14 | 19 | 5 | 0 | 0 | 0 |
| Dry (%) | Comfortable (%) | Humid (%) | Muggy (%) | |
|---|---|---|---|---|
| Jan | 100 | 0 | 0 | 0 |
| Feb | 100 | 0 | 0 | 0 |
| Mar | 100 | 0 | 0 | 0 |
| Apr | 98 | 2 | 0 | 0 |
| May | 75 | 23 | 2 | 0 |
| Jun | 27 | 42 | 27 | 4 |
| Jul | 14 | 31 | 42 | 14 |
| Aug | 10 | 29 | 42 | 19 |
| Sep | 36 | 33 | 26 | 5 |
| Oct | 67 | 24 | 9 | 0 |
| Nov | 93 | 7 | 1 | 0 |
| Dec | 100 | 0 | 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 Siena is steady company: average speeds sit near 8 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) | 8 | 9 | 9 | 8 | 8 | 7 | 7 | 7 | 8 | 8 | 8 | 8 |
| Feels | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm |
| Wind speed (km/h) | Feels | |
|---|---|---|
| Jan | 8 | calm |
| Feb | 9 | calm |
| Mar | 9 | calm |
| Apr | 8 | calm |
| May | 8 | calm |
| Jun | 7 | calm |
| Jul | 7 | calm |
| Aug | 7 | calm |
| Sep | 8 | calm |
| Oct | 8 | calm |
| Nov | 8 | calm |
| Dec | 8 | calm |
Best time to visit Siena
To characterize how pleasant the weather is in Siena throughout the year, we compute two travel scores — one for general sightseeing, one for beach and pool weather.
Around mid October, Siena is still near the tail of its best-weather window — great conditions with the peak-season crowds already thinning.
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 Siena for general outdoor tourist activities is from early May to late October, with a peak score in the last week of June.
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) | 1.9 | 2.5 | 4.2 | 5.4 | 6.6 | 7.3 | 6.6 | 6.3 | 7.1 | 6.1 | 3.8 | 2.2 |
| Rating | poor | poor | fair | fair | good | good | good | good | good | good | fair | poor |
| Travel score (0–10) | Rating | |
|---|---|---|
| Jan | 1.9 | poor |
| Feb | 2.5 | poor |
| Mar | 4.2 | fair |
| Apr | 5.4 | fair |
| May | 6.6 | good |
| Jun | 7.3 | good |
| Jul | 6.6 | good |
| Aug | 6.3 | good |
| Sep | 7.1 | good |
| Oct | 6.1 | good |
| Nov | 3.8 | fair |
| Dec | 2.2 | poor |
The beach/pool score favors clear, rainless days with daytime highs between 24°C and 34°C. Based on this score, the best time of year to visit Siena for hot-weather activities is from mid June to mid September, with a peak score in the third week of July.
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 Siena, 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 August (highs near 29°C), the essentials are light clothes and sun protection. In the cold season around January (highs near 9°C), pack a warm layer and rain gear.
In August, Siena sees daytime highs around 29°C and nights near 18°C. Pack light clothes and sun protection. About 6 days see rain.
UV index (midday) in Siena 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 Siena peaks around July 14 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 23 at about 1 (low).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 1 | 3 | 5 | 6 | 6 | 8 | 9 | 7 | 5 | 3 | 2 | 1 |
| Level | Low | Moderate | Moderate | High | High | Very high | Very high | Very high | High | Moderate | Moderate | Low |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 1 | Low |
| Feb | 3 | Moderate |
| Mar | 5 | Moderate |
| Apr | 6 | High |
| May | 6 | High |
| Jun | 8 | Very high |
| Jul | 9 | Very high |
| Aug | 7 | Very high |
| Sep | 5 | High |
| Oct | 3 | Moderate |
| Nov | 2 | Moderate |
| Dec | 1 | Low |
Average hourly UV index in Siena
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 July the burn window is concentrated in the middle of the day: about 8.5 hours a day reach index 3 (protection recommended), and 5.5 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) | 0 | 0 | 5 | 6.5 | 7 | 8.5 | 8.5 | 7.5 | 5.5 | 2 | 0 | 0 |
| UV ≥ 6 (h/day) | 0 | 0 | 0 | 0 | 2 | 5 | 5.5 | 3.5 | 0 | 0 | 0 | 0 |
| UV ≥ 3 (h/day) | UV ≥ 6 (h/day) | |
|---|---|---|
| Jan | 0 | 0 |
| Feb | 0 | 0 |
| Mar | 5 | 0 |
| Apr | 6.5 | 0 |
| May | 7 | 2 |
| Jun | 8.5 | 5 |
| Jul | 8.5 | 5.5 |
| Aug | 7.5 | 3.5 |
| Sep | 5.5 | 0 |
| Oct | 2 | 0 |
| Nov | 0 | 0 |
| Dec | 0 | 0 |
Air quality in Siena 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 Siena is worst in March — around 17 µg/m³ PM2.5 (moderate), and holds fairly steady the rest of the year.
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 14 | 14 | 17 | 16 | 15 | 14 | 12 | 13 | 12 | 13 | 12 | 12 |
| Level | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Good | Moderate | Moderate | Moderate | Good | Moderate |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 14 | Moderate |
| Feb | 14 | Moderate |
| Mar | 17 | Moderate |
| Apr | 16 | Moderate |
| May | 15 | Moderate |
| Jun | 14 | Moderate |
| Jul | 12 | Good |
| Aug | 13 | Moderate |
| Sep | 12 | Moderate |
| Oct | 13 | Moderate |
| Nov | 12 | Good |
| Dec | 12 | Moderate |
Growing season
Siena is mild enough that a frost-free day stays more likely than not even in midwinter. Nights are reliably above freezing from about March 12 to November 21 (255 days); outside that window a hard frost is an occasional risk.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frost-free chance (%) | 69 | 72 | 91 | 99 | 100 | 100 | 100 | 100 | 100 | 100 | 93 | 74 |
| Frost nights | 31 | 28 | 12 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 10 | 31 |
| Frost-free chance (%) | Frost nights | |
|---|---|---|
| Jan | 69 | 31 |
| Feb | 72 | 28 |
| Mar | 91 | 12 |
| Apr | 99 | 0 |
| May | 100 | 0 |
| Jun | 100 | 0 |
| Jul | 100 | 0 |
| Aug | 100 | 0 |
| Sep | 100 | 0 |
| Oct | 100 | 0 |
| Nov | 93 | 10 |
| Dec | 74 | 31 |
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. Siena banks about 1,851 degree days a year, and the running total — which growers use to time plantings and predict maturity — climbs fastest around August.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Growing degree days (°C·days) | 0 | 0 | 2 | 66 | 196 | 313 | 411 | 415 | 278 | 150 | 20 | 0 |
| Growing degree days (°C·days) | |
|---|---|
| Jan | 0 |
| Feb | 0 |
| Mar | 2 |
| Apr | 66 |
| May | 196 |
| Jun | 313 |
| Jul | 411 |
| Aug | 415 |
| Sep | 278 |
| Oct | 150 |
| Nov | 20 |
| Dec | 0 |
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.
Siena receives about 4.1 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 1.4 and 7.1 kWh/m².
The brighter stretch of the year lasts 6.0 months, from around Mar 21 to Sep 19. The brightest month is July, averaging about 6.9 kWh/m² (intense).
The dimmest month is December, down near 1.5 kWh/m² — roughly 79% less than the July peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar energy (kWh/m²) | 1.7 | 2.6 | 3.9 | 5.1 | 6.1 | 6.8 | 7.0 | 6.1 | 4.4 | 2.9 | 1.8 | 1.4 |
| Level | Dim | Moderate | Moderate | Bright | Intense | Intense | Intense | Intense | Bright | Moderate | Dim | Dim |
| Solar energy (kWh/m²) | Level | |
|---|---|---|
| Jan | 1.7 | Dim |
| Feb | 2.6 | Moderate |
| Mar | 3.9 | Moderate |
| Apr | 5.1 | Bright |
| May | 6.1 | Intense |
| Jun | 6.8 | Intense |
| Jul | 7.0 | Intense |
| Aug | 6.1 | Intense |
| Sep | 4.4 | Bright |
| Oct | 2.9 | Moderate |
| Nov | 1.8 | Dim |
| Dec | 1.4 | Dim |
Where is Siena?
Siena sits at 43.3°N, 11.3°E, 322 m above sea level, in Italy. The nearest listed city is Colle di Val d'Elsa, 20 km away.
What Siena looks like
Topography around Siena
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Siena.
Within 3 km, the terrain around Siena has only modest variations in elevation — a maximum elevation change of 199 m around an average of 283 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 520 m; within 80 km, very significant variations in elevation — a maximum elevation change of 1,724 m.
The land around Siena is covered by trees (57%) and grassland (22%) within 3 km, trees (55%) and cropland (24%) within 16 km, and trees (62%) within 80 km.
Italy travel facts
- Travel advisory
- Level 2
- Exercise Increased Caution
- Power plugs
- Type C / F / L
- 230 V · 50 Hz
- Prices
- ≈ 69% of US
- price level, 2025
- GDP per capita
- $43,309
- 2025
- Happiness
- 6.6 / 10
- World Happiness, 2025
- Safe drinking water
- 97%
- of population, 2024
- Homicide rate
- 0.6
- per 100k, 2023
- Road deaths
- 5.3
- per 100k/yr, 2019
- Income group
- High
- World Bank
- English
- Moderate
- EF EPI 513
- 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 Siena (43.3182°, 11.3306°, elevation 322 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).