San Francisco weather by month — averages, rainfall & climate trends
Wrapped in fog and cooled by the Pacific, San Francisco has one of the mildest, most even climates in North America — cool, grey summers that cheerfully defy the California stereotype. Average temperatures and rainfall by month, a climate graph, today's conditions versus the long-term average, and how the climate has shifted since 1940 — all on one page for San Francisco, United States.
Today vs average
−0.1°Cabout average
How it’s changed
Right now
What it's doing today vs the historical average for this date.
Right now
18.2°
19°12°20°12°
25°13°23°17°21°15°21°14°23°14°On this date — July 20
About average
- Record high: 23.8° · 2024
- Record low: 10.6° · 1982
- One year ago: 15.6°
Every July 20 in history — coldest to hottest
Dots show daily highs (top) and lows (bottom) for each July 20 on record (n = 87). Outlined dots are today's forecast.
Area we sample
Each city's history comes from one ERA5 grid cell — about 28 km across, shown by the dashed box. Near mountains or coasts, conditions can vary across the cell.
Location & data
Historical weather for San Francisco is sampled from the ECMWF ERA5 reanalysis at 37.77°N, 122.42°W, with daily records since 1940.
- Coordinates
- 37.77°N, 122.42°W
- Time zone
- America/Los Angeles
- Period
- 1940–2026
- Data source
- ERA5 (ECMWF)
Last 30 days
13 of the last 31 days were warmer than the historical average for that date. Average difference: +0.3°C.
Each bar is one day, from morning low to afternoon high. Warm-colored bars are days whose mean ran above average; cool bars ran below. The dot inside the bar is the daily mean. The shaded band is the typical 10–90% range expected for that date. Average = the day's mean temperature averaged across every year of record (1940–2026) for that calendar date.
This date over the years
One dot per year — the mean temperature on this calendar date. Dots are warmer or cooler than the long-term average (dashed line); the shaded band is the typical 10–90% range, and the highlighted dot is today's forecast. Based on ERA5 reanalysis — modelled estimates, not station readings.
Weather by month
Average temperatures and rainfall for each month — what a typical year looks like, from the full record.Climate overview
San Francisco occupies the tip of a hilly peninsula between the Pacific Ocean and San Francisco Bay, giving it a warm-summer Mediterranean climate (Köppen Csb) that is unusually cool and even for California. Every month is mild and summers in particular stay cool: warm, moist ocean air meeting cold water welling up along the coast condenses into the persistent fog and low cloud that pour through the Golden Gate on summer afternoons. Sharp microclimates mean fog-bound western districts can be markedly cooler than sunnier, sheltered neighbourhoods only a few kilometres away.
The fog is driven by heat in California's interior valleys, which forms a low-pressure zone that draws cool Pacific air in through the Golden Gate. Rain is confined almost entirely to the winter half of the year, in classic Mediterranean fashion, leaving the city's summers dry as well as cool.
The warmest month is September, with a daily mean around 16.2°C and typical afternoon highs of 20.1°C. The coolest month is January, when daily means fall to about 10.0°C and overnight lows sit around 7.7°C. Freezing temperatures almost never occur.
San Francisco picks up roughly 556 mm a year, with a peak of 106 mm in January and as little as 2 mm in July. Rain falls on only around 60 days in a typical year.
The record here starts in 1940, and since then the annual mean in San Francisco has climbed 0.7°C from the first ten years to the last ten. You can follow the shift year by year in the charts above.
Climate graph (climograph)
September is the warmest month, January the coolest — a yearly swing of 6°C. Wettest month: January (~106 mm). Whole year averages ~556 mm of rain.
Bars = average monthly rainfall (right axis). Lines = average daily high and low (left axis). Average = each month's value averaged across every year of record (1940–2026).
Monthly wind
Average daily peak wind at 10 m, by month.
Monthly solar energy
Average daily incoming solar energy in megajoules per square metre — a measured proxy for how sunny the month is.
San Francisco month by month — what to expect
Typical conditions for each month, averaged across the full record (since 1940). Daylight is the time from sunrise to sunset. Record high/low are the most extreme values in the ERA5 dataset (modelled since 1940), so they can differ from official weather-station readings.
| Month | Avg high | Avg low | Rain | Daylight | Record high | Record low |
|---|---|---|---|---|---|---|
| January | 13.1° | 7.7° | 106 mm | 9.7 h | 21.8° (1962) | -0.5° (1949) |
| February | 14.1° | 8.6° | 101 mm | 10.6 h | 21.1° (1986) | -0.5° (1989) |
| March | 14.7° | 9.3° | 83 mm | 11.7 h | 24.5° (1972) | 3.4° (1966) |
| April | 15.6° | 9.9° | 41 mm | 13.0 h | 28.1° (2022) | 4.7° (1976) |
| May | 16.7° | 11.0° | 18 mm | 14.0 h | 31.0° (2008) | 7.1° (1950) |
| June | 18.2° | 12.1° | 5 mm | 14.6 h | 31.0° (2019) | 8.6° (1999) |
| July | 18.9° | 12.8° | 2 mm | 14.4 h | 27.8° (1959) | 9.7° (1955) |
| August | 19.3° | 13.4° | 3 mm | 13.5 h | 31.4° (1968) | 9.8° (1955) |
| September | 20.1° | 13.6° | 5 mm | 12.2 h | 35.3° (2017) | 9.6° (1950) |
| October | 19.1° | 12.6° | 27 mm | 11.0 h | 33.2° (1987) | 6.8° (1946) |
| November | 16.0° | 10.3° | 65 mm | 9.9 h | 26.6° (1949) | 3.7° (1952) |
| December | 13.4° | 8.2° | 100 mm | 9.4 h | 20.4° (2020) | -2.3° (1990) |
How it has changed
Year-by-year signals from 1940 to today.Climate stripes
Annual mean shifted from 1940–1949 to 2016–2025 by +0.7°C.
Each vertical stripe is one year. Color encodes how much that year's annual mean differed from the long-term average. Average = each year's annual mean compared to the average of all years (1940–2026). cooler ← → warmer
Annual mean temperature
Long-term trend: +0.08°C per decade.
One point per year — the temperature averaged across the whole year. The dashed line is the least-squares long-term trend. Based on ERA5 reanalysis — modelled estimates, not station readings.
Seasonal warming
Dec–Feb is warming fastest: +0.14°C per decade.
Each faint line is one three-month period's average per year; the bold dashed line is its long-term trend. Different parts of the year often warm at different rates. Based on ERA5 reanalysis — modelled estimates, not station readings.
Hot days vs frost days
Days ≥ 25°C per year: 5.7 early in the record → 6.1 recently. Frost days: 0 → 0.
Thin lines are raw yearly counts; thick lines are the smoothed trend that removes year-to-year noise. The hot-day threshold is auto-picked per city so the line actually moves. Average = a centered 5-year rolling average to smooth weather noise.
Yearly hot & cold extremes
All-time high in 2017, all-time low in 1990: 35.3°C / -2.3°C.
One point per year — the single hottest and coldest day recorded that year.
Annual rainfall
~556 mm/year on average. Last decade ran +4% vs that average. Long-term trend: +3 mm per decade.
One bar per year of total rainfall. Dashed line is the long-term average. Average = the average annual rainfall across every year of record (1940–2026).
Day-by-day grid
Each tiny square is one calendar day across the full record — ~30,000 days per city. Use the mode switch above the chart: Anomaly colors each day by how far it ran from the historical average for that date (red = warmer, blue = cooler), Daily mean temp shows the absolute mean temperature for the day (useful to see seasons and heatwaves), and Precipitation shows daily rainfall (useful to spot wet/dry seasons and droughts). Average = the long-term average for that calendar date (1940–2026).