Portola Valley, CA climate
Portola Valley has warm winters and pleasant summers. A typical July afternoon reaches 80°, a January night drops to 41°, and snow is almost unheard of.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Portola Valley feels like
Winter
Spring
Summer
Fall
Portola 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 | 57° | 41° | 7.4" | 0 | 9 | 0 | 46° – 54° |
| February | 58° | 41° | 7.2" | 0 | 9 | 0 | 45° – 55° |
| March | 61° | 41° | 5.5" | 0 | 9 | 0 | 47° – 56° |
| April | 64° | 42° | 2.7" | 0 | 5 | 0 | 49° – 56° |
| May | 69° | 46° | 1.1" | 0 | 3 | 0 | 53° – 62° |
| June | 75° | 49° | 0.3" | 0 | 1 | 0 | 59° – 65° |
| July | 80° | 53° | 0.0" | 0 | 0 | 0 | 64° – 70° |
| August | 80° | 54° | 0.1" | 0 | 0 | 0 | 65° – 71° |
| September | 79° | 54° | 0.1" | 0 | 1 | 0 | 63° – 71° |
| October | 73° | 50° | 1.6" | 0 | 3 | 0 | 59° – 68° |
| November | 63° | 44° | 3.8" | 0 | 6 | 0 | 47° – 57° |
| December | 57° | 40° | 7.4" | 0 | 9 | 0 | 45° – 53° |
| Year | 68° | 46° | 37.0" | 0.0" | 55 | 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 Portola Valley
Portola Valley gets 37 inches of rain and melted snow a year. January is the wettest month and July the driest. Rain or snow falls on about 55 days a year.
About 275 frost-free days a year
In half of years the last 32° night comes by March 21 and the first one by December 15. That leaves about 275 frost-free days for gardens, longer than 93% of U.S. towns.
Heating and cooling a home in Portola Valley
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Portola Valley, 83% of that work is heating and 17% 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.
Portola Valley and its neighbors
Portola Valley borders 3 towns with climate data. January nights across them vary by 1.6°. Ladera has both the coldest January nights (40°) and the hottest July afternoons (81°). Portola Valley’s January low is 41° and its July high 80°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How Portola 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 Portola Valley averaged 1.8° warmer than the 1900s. The biggest change is in August (+2.3°). The shift is larger than in 89% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Portola 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 47° to 56°. August is the most reliable, staying within 6°.
Common questions about Portola Valley’s climate
What is the coldest month in Portola Valley?
December, with a typical high of 57° and a low of 40°.
What is the hottest month in Portola Valley?
August, with a typical high of 80° and a low of 54°. About 13 days a year reach 90°.
How much snow does Portola Valley get?
Almost none. A normal year brings 0.0 inches.
When is the first frost in Portola Valley?
In half of years the first 32° night comes by December 15, and the last spring frost by March 21.
What is the rainiest month in Portola Valley?
January, with 7.4 inches of rain and melted snow. The year totals 37 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Portola Valley itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Redwood City, CA (8 mi, snow) and Skyline Ridge Preserve, CA (4 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.