San Jose weather by month — averages, rainfall & climate trends
The capital of Silicon Valley gets some of the sunniest, driest weather on the California coast, thanks to a wall of mountains that strips out the rain before it reaches the valley floor. 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 Jose, United States.
Today vs average
+0.6°Cabout average
How it’s changed
Right now
What it's doing today vs the historical average for this date.
Right now
22.2°
29°16°
28°14°36°16°31°18°33°17°33°17°36°17°On this date — July 20
About average
- Record high: 35.8° · 1960
- Record low: 10.1° · 1949
- One year ago: 24.7°
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 Jose is sampled from the ECMWF ERA5 reanalysis at 37.34°N, 121.89°W, with daily records since 1940.
- Coordinates
- 37.34°N, 121.89°W
- Time zone
- America/Los Angeles
- Period
- 1940–2026
- Data source
- ERA5 (ECMWF)
Last 30 days
5 of the last 31 days were warmer than the historical average for that date. Average difference: −0.5°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 Jose lies at the southern end of the Santa Clara Valley, hemmed in by hills on three sides. The Santa Cruz Mountains to the west cast a long rain shadow over the city, leaving it noticeably drier than the coast just beyond and giving it close to 300 sunny days in a typical year. Its climate is warm-summer Mediterranean (Köppen Csb): warm, rainless summers and cool, damp winters, with the year's rain packed into a few months.
Whatever rain arrives comes almost entirely in winter, and the valley has long lived with extended dry spells and recurring drought. The sharpest recent shock landed on 16 August 2020, when an unusual siege of dry thunderstorms threw hundreds of lightning strikes at parched hillsides and ignited some of the largest wildfires the region had ever recorded.
August brings the year's peak warmth: daily means of 20.1°C, with afternoons typically reaching 27.8°C. At the other extreme, January averages 10.1°C, with typical overnight lows of 6.5°C. Freezing temperatures almost never occur.
In total, San Jose averages about 631 mm of precipitation a year; January is usually the wettest month (119 mm) and July the driest (1 mm). A typical year sees rain on just 55 days or so.
Comparing the record's first decade with its most recent one, San Jose now averages 1.2°C warmer than it did in the 1940s. The count of days past 30°C has eased from roughly 50 a year to about 30 over the record.
Climate graph (climograph)
August is the warmest month, January the coolest — a yearly swing of 10°C. Wettest month: January (~119 mm). Whole year averages ~631 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 Jose 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 | 15.2° | 6.5° | 119 mm | 9.7 h | 26.1° (2014) | -2.5° (1949) |
| February | 16.6° | 7.5° | 118 mm | 10.6 h | 28.3° (1987) | -1.3° (1989) |
| March | 17.8° | 8.3° | 101 mm | 11.7 h | 30.3° (2015) | 0.3° (1966) |
| April | 20.0° | 9.3° | 51 mm | 13.0 h | 33.9° (1996) | 2.6° (1976) |
| May | 22.4° | 10.9° | 20 mm | 14.0 h | 36.3° (1951) | 4.0° (1952) |
| June | 25.6° | 12.7° | 4 mm | 14.6 h | 40.9° (2000) | 6.0° (1962) |
| July | 27.9° | 14.2° | 1 mm | 14.3 h | 41.3° (1972) | 8.7° (1977) |
| August | 27.8° | 14.6° | 2 mm | 13.4 h | 41.5° (1950) | 8.8° (1955) |
| September | 27.5° | 14.7° | 5 mm | 12.2 h | 42.9° (1950) | 7.1° (1950) |
| October | 24.3° | 12.6° | 29 mm | 11.0 h | 39.6° (2024) | 3.8° (1946) |
| November | 19.0° | 9.2° | 72 mm | 10.0 h | 32.6° (1949) | 0.4° (2010) |
| December | 15.4° | 7.0° | 110 mm | 9.4 h | 26.9° (1958) | -3.9° (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 +1.2°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: +0.14°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: +0.24°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 ≥ 30°C per year: 48.8 early in the record → 31.7 recently. Frost days: 2 → 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 1950, all-time low in 1990: 42.9°C / -3.9°C.
One point per year — the single hottest and coldest day recorded that year.
Annual rainfall
~631 mm/year on average. Last decade ran +9% vs that average. Long-term trend: +7 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).