Mill Valley, United States experiences average highs of 19°C (66°F) and lows of 10°C (50°F) throughout the year. The climate is relatively dry, with only 4 rainy days per month on average. Sunshine is abundant, averaging about 10 hours per day. Average highs have stayed broadly stable across the available records.
Mill Valley, United States Weather & Climate 2026
Monthly climate averages for Mill Valley, United States. Based on 10-year ERA5 reanalysis data.
Climate Overview
Drier season: May–Oct 
Wetter season: Jan–Dec At-a-Glance Climate Summary
Live Weather & Air Quality
Key figures
Climate Score
7.8/10
Best: June, July, August, September, October
UV Index
6
High
Temperature 19°C / 10°C
Feels Like 18°C / 9°C
Rainy Days 4
Rainfall 48 mm
Sunshine 10 h
Humidity 76%
Wind Speed 18 km/h
Dew Point 10°C
Hottest Month
23°C
September
Avg Low14°C
Rain0days
Coldest Month
7°C
January
Avg High14°C
Rain11days
Driest Month
0days
June
Avg High22°C
Avg Low12°C
Windiest Month
22 km/h
May (Gusts 42)
Sea Temperature
12°C – 17°C
Warmest water: September (
16.8°C
)
Worst Time to Visit
Consider avoiding January, February, March, December due to less favorable weather conditions.
Sun Position
Sunrise 05:49
Daylight 14.8h
Sunset 20:35
Live conditions—
Mill Valley on the map · live conditions
Mill Valley, United States
- Continent
- Americas
- Country
- United States
- City
- Mill Valley
- Population
- 14.4K
- Elevation
- 24 m
- Coordinates
- 37.91°, -122.54°
Seasonal Breakdown
Spring
Mar–May
Avg High 17°C
Avg Low 9°C
Rain 6 days/mo
Summer
Jun–Aug
Avg High 22°C
Avg Low 13°C
Rain 0 days/mo
3/3 best months
Autumn
Sep–Nov
Avg High 21°C
Avg Low 12°C
Rain 3 days/mo
2/3 best months
Winter
Dec–Feb
Avg High 14°C
Avg Low 7°C
Rain 9 days/mo
Climate Charts
Based on historical averages (2016–2025)
Monthly Temperatures
HighLowShaded bands show the typical range across the available yearly records.
Line chart showing monthly temperatures. Jan: 14°C / 7°C . Feb: 15°C / 7°C . Mar: 16°C / 8°C . Apr: 18°C / 9°C . May: 19°C / 11°C . Jun: 22°C / 12°C . Jul: 22°C / 13°C . Aug: 23°C / 14°C . Sep: 23°C / 14°C . Oct: 22°C / 12°C . Nov: 17°C / 9°C . Dec: 14°C / 7°C .
Monthly Rainfall
Rainfall
Bar chart showing monthly rainfall. Jan: 123 mm. Feb: 105 mm. Mar: 100 mm. Apr: 28 mm. May: 15 mm. Jun: 1 mm. Jul: 0 mm. Aug: 0 mm. Sep: 3 mm. Oct: 30 mm. Nov: 59 mm. Dec: 108 mm.
Monthly Humidity
Humidity
Line chart showing monthly humidity. Jan: 83%. Feb: 77%. Mar: 78%. Apr: 75%. May: 73%. Jun: 71%. Jul: 76%. Aug: 77%. Sep: 75%. Oct: 71%. Nov: 77%. Dec: 82%.
Monthly Wind Speed
Wind SpeedGusts
Bar chart showing monthly wind speed. Jan: 17 km/h . Feb: 19 km/h . Mar: 20 km/h . Apr: 21 km/h . May: 22 km/h . Jun: 21 km/h . Jul: 19 km/h . Aug: 19 km/h . Sep: 18 km/h . Oct: 16 km/h . Nov: 15 km/h . Dec: 16 km/h .
Sunshine
Sunshine
Sunshine: Jan: 7h. Feb: 8h. Mar: 9h. Apr: 11h. May: 12h. Jun: 13h. Jul: 13h. Aug: 12h. Sep: 11h. Oct: 9h. Nov: 8h. Dec: 6h.
Sea Temperature
Sea Temperatureswim
Line chart showing monthly sea temperature. Jan: 12°C . Feb: 12°C . Mar: 12°C . Apr: 13°C . May: 14°C . Jun: 15°C . Jul: 15°C . Aug: 16°C . Sep: 17°C . Oct: 17°C . Nov: 14°C . Dec: 12°C .
UV Index
UV Index
Bar chart showing monthly UV index. Jan: UV 3. Feb: UV 4. Mar: UV 5. Apr: UV 7. May: UV 8. Jun: UV 8. Jul: UV 8. Aug: UV 7. Sep: UV 6. Oct: UV 5. Nov: UV 3. Dec: UV 3.
Monthly Daylight Hours
Daylight12h reference
Monthly Dew Point & Comfort
Dew Point Dry Comfortable Humid Muggy Oppressive
Climate Trends
Average highs have stayed broadly stable across the available records. Average rainfall is trending drier by about 17 mm.
2016 to 2025
Avg high Avg rainfall
Climate summary
| Last 12 months | All years | |
|---|---|---|
| Hottest month | Aug 2025 · 23°C | Sep · 23°C |
| Coldest month | Jan 2025 · 6°C | Jan · 7°C |
| Wettest month | Feb 2025 · 157 mm | Jan · 123 mm |
| Windiest month | May 2025 · 23 km/h | May · 22 km/h |
Month-by-Month Weather Table
January
Fair 
February
Fair March
Fair April
Good May
Good June best
Excellent July best
Excellent August best
Excellent September best
Excellent October best
Excellent November
Good December
Fair | Month | Temp | Feels Like | Rain | Sun | Humidity | UV | Status | Details |
|---|---|---|---|---|---|---|---|---|
| January | 14°C / 7°C | 12°C / 5°C | 11days (123 mm) Wet | 6.5h Fair | 83% Humid | 2.8 Moderate | Fair | View Details |
| February | 15°C / 7°C | 13°C / 5°C | 7days (105 mm) Good | 8.2h Good | 77% Humid | 3.7 Moderate | Fair | View Details |
| March | 16°C / 8°C | 14°C / 6°C | 11days (100 mm) Wet | 9.2h Good | 78% Humid | 5.2 High | Fair | View Details |
| April | 18°C / 9°C | 17°C / 7°C | 4days (28 mm) Good | 11h Excellent | 75% Muggy | 6.8 High | Good | View Details |
| May | 19°C / 11°C | 19°C / 9°C | 2days (15 mm) Excellent | 12.4h Excellent | 73% Muggy | 7.8 Very High | Good | View Details |
| June best | 22°C / 12°C | 22°C / 11°C | 0days (1 mm) Excellent | 13.2h Excellent | 71% Muggy | 7.9 Very High | Excellent | View Details |
| July best | 22°C / 13°C | 22°C / 12°C | 0days (0 mm) Excellent | 13h Excellent | 76% Humid | 8 Very High | Excellent | View Details |
| August best | 23°C / 14°C | 23°C / 13°C | 0days (0 mm) Excellent | 12.1h Excellent | 77% Humid | 7.4 Very High | Excellent | View Details |
| September best | 23°C / 14°C | 23°C / 13°C | 0days (3 mm) Excellent | 11.1h Excellent | 75% Muggy | 6.3 High | Excellent | View Details |
| October best | 22°C / 12°C | 21°C / 11°C | 3days (30 mm) Excellent | 9.3h Good | 71% Muggy | 4.8 Moderate | Excellent | View Details |
| November | 17°C / 9°C | 16°C / 8°C | 6days (59 mm) Good | 7.8h Good | 77% Humid | 3.3 Moderate | Good | View Details |
| December | 14°C / 7°C | 12°C / 5°C | 9days (108 mm) Wet | 6.3h Fair | 82% Humid | 2.5 Moderate | Fair | View Details |
Compare Nearby City Climates
Frequently Asked Questions
The best months to visit Mill Valley are June, July, August, September, October, when temperatures are comfortable and rainfall is at its lowest. This is based on 10-year climate averages for Mill Valley, scoring temperature, rainfall, humidity, and sunshine hours.
The hottest month in Mill Valley is September, with average daytime highs of 23°C (74°F). Plan outdoor activities for early morning or late afternoon if visiting during this period.
The coldest month in Mill Valley is January, with average overnight lows of 7°C (45°F). Pack warm layers and expect shorter daylight hours during this period.
The wettest month in Mill Valley is January, averaging 123mm of precipitation across 11 rainy days. An umbrella or waterproof jacket is essential.
The rainy season in Mill Valley runs through January, March, with the heaviest rainfall in January. Based on 10-year averages for Mill Valley.
Mill Valley receives approximately 120 sunshine hours per year. The sunniest month is June with around 13 hours. Based on climate data for Mill Valley.
The least favorable months to visit Mill Valley are January, February, March, December, primarily due to less favorable weather conditions. For the best conditions, consider June, July, August, September, October instead.
The annual average UV index in Mill Valley is 6, classified as high. Standard sun protection (sunscreen, hat) is recommended during prolonged outdoor exposure.
Average humidity in Mill Valley is 76%, classified as humid. Humidity levels are generally comfortable and should not affect outdoor activities for most people.
Sea temperatures in Summer average 14°C (57°F), which most swimmers will find too cold without a wetsuit.
Average wind speeds in Mill Valley are 18 km/h (11 mph). The windiest month is May with peak winds reaching 22 km/h (13 mph) (gusts up to 42 km/h / 26 mph).
Mill Valley averages 8 clear-sky days per month with overall cloud cover around 46%. The clearest skies occur in October.
The annual average dew point in Mill Valley is 10°C (50°F), which feels pleasant with low humidity. Outdoor activities are comfortable year-round from a humidity standpoint.
Mill Valley has a Warm-Summer Mediterranean climate, classified as Csb under the Köppen system. Temperate climates have mild winters and warm summers, with rainfall spread across the year and four distinct seasons.
The 'feels like' temperature in Mill Valley ranges from 9°C (48°F) to 18°C (64°F) on average. The 'feels like' temperature closely matches the actual temperature throughout most of the year.
Yes, June is a great time to visit Mill Valley. It earns a climate score of 9.2/10 with Excellent.
For June in Mill Valley, pack Sunscreen (SPF 30+), Sunglasses, Comfortable walking shoes. With average highs of 22°C (71°F) and 0 rainy days, these essentials will keep you comfortable.
Data Source
Climate data derived from ERA5 reanalysis (ECMWF), averaged over 2016–2025. Sea surface temperature from marine reanalysis data. Climate scores and seasonal estimates are computed by WorldStats.
Last updated: