Photo: SWENOWENSON · CC BY-SA 4.0Mill Valley has some of the coolest summers among U.S. towns
January nights here settle around 43°. A year here swings 30° from midwinter lows to midsummer highs. Winters are mild: January nights here are milder than in 92% of U.S. towns. Homes need heating from December to January, the months averaging under 50°.
A year in Mill Valley at a glance
Each month’s typical high and low, and what it brings.
What stands out about Mill Valley’s climate
Compared with towns across the U.S., with Mill Valley’s place in California beside it.
What a year in Mill Valley feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
Frost is rare
Frost and day counts come from NOAA’s station at Richmond, CA, 9 miles from the town’s center, 220 ft lower.
The 2023 USDA map puts Mill Valley’s center in zone 10a: the coldest night of a typical winter, averaged over 1991–2020, reaches about 31°. Plant labels use the zone; frost dates tell you when to plant.
90° days by month
Average days at 90° or more
About 36 inches of rain a year
December is the wettest month and July the driest. Rain falls on about 96 days a year. Snow is rare: about 0.0" in a normal year at Muir Woods, CA, so most winters see none.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Mill Valley
92% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from November through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Richmond, CA.
Living with Mill Valley’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
Zone 10a. Frost comes about 1 winter in 5, so tender plants can often stay out through winter.
Months with highs of 62–84° and lows of 40° or more: April, May, June, July, August, September and October. 23 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Mill Valley from natural hazards, earthquakes are the largest share (53%); heat waves, cold waves, winter storms and ice storms together are 1%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Mill Valley and its neighbors
Kentfield has the coldest January nights next door (42°, 1° colder) and Kentfield the hottest July afternoons (74°, 2° warmer). Differences under a degree are within what the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Mill Valley’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Mill Valley, CA | 43° | 72° | 36" | 0.0" |
| Mukilteo, WA | 36° | 74° | 35" | 3.0" |
| Makawao, HI | 53° | 75° | 23" | 0.0" |
| West Haven-Sylvan, OR | 36° | 80° | 44" | 3.6" |
| Nantucket, MA | 26° | 76° | 44" | 25" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Mill Valley averaged 1.5° warmer than the 1900s. The biggest change is in January (+2.2°).
A bigger shift than in 56% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Mill Valley compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Mill Valley’s place among California’s.
Mill Valley weather by month
Highs, lows and precipitation from NOAA’s grid at Mill Valley’s center; snow, wet days and snow on the ground from Muir Woods, CA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 56° | 43° | 6.8" | 0.0" | 14 | 0 | 46° – 54° |
| February | 58° | 44° | 6.8" | 0.0" | 13 | 0 | 47° – 57° |
| March | 61° | 45° | 5.0" | 0.0" | 12 | 0 | 48° – 58° |
| April | 63° | 46° | 2.3" | 0.0" | 9 | 0 | 51° – 58° |
| May | 65° | 49° | 1.1" | 0.0" | 5 | 0 | 53° – 62° |
| June | 70° | 51° | 0.3" | 0.0" | 4 | 0 | 57° – 63° |
| July | 72° | 53° | 0.0" | 0.0" | 2 | 0 | 59° – 66° |
| August | 73° | 54° | 0.1" | 0.0" | 3 | 0 | 61° – 67° |
| September | 73° | 54° | 0.1" | 0.0" | 3 | 0 | 59° – 68° |
| October | 70° | 51° | 1.7" | 0.0" | 6 | 0 | 58° – 66° |
| November | 62° | 47° | 3.9" | 0.0" | 10 | 0 | 48° – 57° |
| December | 56° | 43° | 7.8" | 0.0" | 15 | 0 | 46° – 54° |
| Year | 65° | 48° | 35.8" | 0.0" | 96 | 0 |
How much a month can swing
A normal is an average. March swings the most: from 1991 to 2020 its average ranged from 48° to 58°. June is the most reliable, staying within 5°.
Where Mill Valley’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Mill Valley’s center.
- Snow: Muir Woods, CA (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: Richmond, CA, 9 miles from the town’s center, 220 ft lower; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Mill Valley’s climate
What is the weather like in Mill Valley?
A typical July afternoon reaches 72°, a January night drops to 43°, and snow is almost unheard of. Milder January nights than 92% of U.S. towns; cooler July afternoons than all but 103 U.S. towns.
How cold does it get in Mill Valley in winter?
January nights average 43°. A night at 32° or below comes in only some winters (0.3 a year on average). In the coldest January of the last 30 years the month averaged 46°.
How much snow does Mill Valley get?
About 0.0 inches in a normal winter at Muir Woods, CA, so most winters see none.
How hot does it get in Mill Valley?
July, with a typical high of 72° and a low of 53°. About 5 days a year reach 90° (Richmond, CA).
When is the first and last frost in Mill Valley?
Most years have no frost at all: a 32° night comes in about 22% of winters at Richmond, CA, usually in December or January.
What growing zone is Mill Valley in?
Zone 10a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 31°.
What is the best time of year to visit Mill Valley?
By one simple rule (highs of 62–84° and lows of 40° or more), April, May, June, July, August, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Mill Valley getting warmer?
Yes: 1991–2020 averaged 1.5° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 56% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Mill Valley.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.