Mill Valley, CA climate
Mill Valley has warm winters and cool summers. A typical July afternoon reaches 72°, a January night drops to 43°, and snow is almost unheard of.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Mill Valley feels like
Winter
Spring
Summer
Fall
Mill Valley weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 56° | 43° | 6.8" | 0 | 14 | 0 | 46° – 54° |
| February | 58° | 44° | 6.8" | 0 | 13 | 0 | 47° – 57° |
| March | 61° | 45° | 5.0" | 0 | 12 | 0 | 48° – 58° |
| April | 63° | 46° | 2.3" | 0 | 9 | 0 | 51° – 58° |
| May | 65° | 49° | 1.1" | 0 | 5 | 0 | 53° – 62° |
| June | 70° | 51° | 0.3" | 0 | 4 | 0 | 57° – 63° |
| July | 72° | 53° | 0.0" | 0 | 2 | 0 | 59° – 66° |
| August | 73° | 54° | 0.1" | 0 | 3 | 0 | 61° – 67° |
| September | 73° | 54° | 0.1" | 0 | 3 | 0 | 59° – 68° |
| October | 70° | 51° | 1.7" | 0 | 6 | 0 | 58° – 66° |
| November | 62° | 47° | 3.9" | 0 | 10 | 0 | 48° – 57° |
| December | 56° | 43° | 7.8" | 0 | 15 | 0 | 46° – 54° |
| Year | 65° | 48° | 35.8" | 0.0" | 96 | 0 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in Mill Valley
Mill Valley gets 36 inches of rain and melted snow a year. December is the wettest month and July the driest. Rain or snow falls on about 96 days a year.
A year-round growing season
Heating and cooling a home in Mill Valley
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Mill Valley, 92% of that work is heating and 8% is cooling, so the furnace matters far more than the air conditioner.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
Mill Valley and its neighbors
Mill Valley borders 6 towns with climate data. January nights across them vary by 2.2°. Kentfield has both the coldest January nights (42°) and the hottest July afternoons (74°). Mill Valley’s January low is 43° and its July high 72°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How Mill Valley compares
Compared with every U.S. town and city on TownTapestry, each counted once.
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°). The shift is larger than in 67% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Mill Valley’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. March swings the most: between 1991 and 2020 its average temperature ranged from 48° to 58°. June is the most reliable, staying within 5°.
Common questions about Mill Valley’s climate
What is the coldest month in Mill Valley?
January, with a typical high of 56° and a low of 43°.
What is the hottest month in Mill Valley?
September, with a typical high of 73° and a low of 54°. About 5 days a year reach 90°.
How much snow does Mill Valley get?
Almost none. A normal year brings 0.0 inches.
When is the first frost in Mill Valley?
Frost is uncommon. Only 22% of years see a night at 32° or below.
What is the rainiest month in Mill Valley?
December, with 7.8 inches of rain and melted snow. The year totals 36 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Mill Valley itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Muir Woods, CA (2 mi, snow) and Richmond, CA (9 mi, frost, heat and degree days). Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.