Photo: Pi.1415926535 · CC BY-SA 3.0Foster City’s winters are milder and less snowy than most of the U.S.
A typical July afternoon reaches 72°, a January night drops to 44°, and snow is almost unheard of.
A year in Foster City at a glance
Each month’s typical high and low, and what it brings.
What stands out about Foster City’s climate
Compared with towns across the U.S., with Foster City’s place in California beside it.
What a year in Foster City 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 San Francisco International Airport, 7 miles from the town’s center, at about the same height.
The 2023 USDA map puts Foster City’s center in zone 10a: the coldest night of a typical winter, averaged over 1991–2020, reaches about 32°. Plant labels use the zone; frost dates tell you when to plant.
90° days by month
Average days at 90° or more
About 19 inches of rain a year
December is the wettest month and July the driest. Rain falls on about 63 days a year. Snow is rare: about 0.0" in a normal year at Oakland Museum, CA, so most winters see none.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Foster City
93% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from December through February.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at San Francisco International Airport.
Living with Foster City’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 9, so tender plants can often stay out through winter.
Months with highs of 62–84° and lows of 40° or more: March, April, May, June, July, August, September, October and November. 9.0 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Foster City from natural hazards, river flooding is the largest share (58%); heat waves, cold waves, winter storms and ice storms together are 1%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Foster City and its neighbors
Belmont has the coldest January nights next door (42°, 3° colder) and Hayward the hottest July afternoons (78°, 7° 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 Foster City’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 |
|---|---|---|---|---|
| Foster City, CA | 44° | 72° | 19" | 0.0" |
| Sequim, WA | 34° | 71° | 18" | 1.4" |
| Makawao, HI | 53° | 75° | 23" | 0.0" |
| Cedar Mill, OR | 36° | 81° | 39" | 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 Foster City averaged 1.6° warmer than the 1900s. The biggest change is in January (+2.2°).
A bigger shift than in 68% 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 Foster City compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Foster City’s place among California’s.
Foster City weather by month
Highs, lows and precipitation from NOAA’s grid at Foster City’s center; snow, wet days and snow on the ground from Oakland Museum, CA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 59° | 44° | 3.7" | 0.0" | 10 | 0 | 49° – 55° |
| February | 61° | 46° | 3.7" | 0.0" | 10 | 0 | 50° – 58° |
| March | 63° | 48° | 2.8" | 0.0" | 10 | 0 | 50° – 60° |
| April | 65° | 49° | 1.4" | 0.0" | 6 | 0 | 53° – 60° |
| May | 68° | 52° | 0.6" | 0.0" | 4 | 0 | 56° – 65° |
| June | 71° | 54° | 0.2" | 0.0" | 1 | 0 | 59° – 65° |
| July | 72° | 56° | 0.0" | 0.0" | 0 | 0 | 61° – 67° |
| August | 72° | 57° | 0.0" | 0.0" | 0 | 0 | 62° – 67° |
| September | 73° | 56° | 0.1" | 0.0" | 1 | 0 | 61° – 68° |
| October | 71° | 53° | 0.9" | 0.0" | 3 | 0 | 59° – 67° |
| November | 64° | 48° | 1.8" | 0.0" | 7 | 0 | 50° – 59° |
| December | 59° | 44° | 3.8" | 0.0" | 11 | 0 | 48° – 56° |
| Year | 66° | 50° | 19.0" | 0.0" | 63 | 0 |
How much a month can swing
A normal is an average. March swings the most: from 1991 to 2020 its average ranged from 50° to 60°. August is the most reliable, staying within 6°.
Where Foster City’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 Foster City’s center.
- Snow: Oakland Museum, CA.
- Frost, freezing nights, 90° and 100° days, heating and cooling: San Francisco International Airport, 7 miles from the town’s center, at about the same height; 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 Foster City’s climate
What is the weather like in Foster City?
A typical July afternoon reaches 72°, a January night drops to 44°, and snow is almost unheard of. Milder January nights than 93% of U.S. towns; cooler July afternoons than all but 107 U.S. towns.
How cold does it get in Foster City in winter?
December nights average 44°. A night at 32° or below comes in only some winters (0.2 a year on average). In the coldest December of the last 30 years the month averaged 48°.
How much snow does Foster City get?
About 0.0 inches in a normal winter at Oakland Museum, CA, so most winters see none.
How hot does it get in Foster City?
July, with a typical high of 72° and a low of 56°. About 4 days a year reach 90° (San Francisco International Airport).
When is the first and last frost in Foster City?
Most years have no frost at all: a 32° night comes in about 12% of winters at San Francisco International Airport, usually in December or January.
What growing zone is Foster City in?
Zone 10a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 32°.
What is the best time of year to visit Foster City?
By one simple rule (highs of 62–84° and lows of 40° or more), March, April, May, June, July, August, September, October and November. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Foster City getting warmer?
Yes: 1991–2020 averaged 1.6° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 68% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Foster City.
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.