Vallejo (CA) Temperature by Month
Vallejo, California, United States of America has an average annual maximum temperature of 21°C (70°F), ranging from 14°C (57°F) in December to 27°C (81°F) in September. Below you'll find a full monthly breakdown and a comparison with cities worldwide.
Vallejo Monthly Temperatures
With significant temperature fluctuations, Vallejo enjoys distinct seasons year-round. Nighttime lows range from 12°C (54°F) in September to 4°C (39°F) in December.
The chart below illustrates the average maximum day and minimum night temperatures in Vallejo by month:
Temperatures tend to bottom out between 4 AM and 6 AM, then climb to their daily peak around 3 PM. September, the warmest month, sees 270 hours of sunshine.
The chart below shows the average temperature throughout the year:
Temperature: Vallejo vs the United States of America
The map below shows the annual temperature across the United States of America. You can also select individual months if you want to compare a specific time of year.
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Vallejo vs World: Temperature Compared
Vallejo's average annual maximum temperature is 21°C (70°F). To put that in context, here's how it compares to a few well-known destinations:
Lisbon, Portugal averages 21°C (70°F) annually — warm summers, mild winters, and rain mainly in the cooler months.
Reykjavík, Iceland averages 9°C (48°F) a year — mild summers by Icelandic standards, but cold winters and frequent wind.
Osaka, Japan averages 22°C (72°F) annually, with hot humid summers, mild winters, and pleasant spring and autumn seasons.
Adelaide, Australia averages 21°C (70°F) a year, with warm summers, mild winters, and relatively low rainfall year-round.
What Does the Temperature Feel Like in Vallejo?
Temperature alone doesn't tell the whole story — humidity plays a big role in how warm or cold it actually feels. High humidity in summer makes the heat feel more intense, particularly once temperatures climb above 25°C. In winter, the same humidity can make cold air feel sharper than the thermometer suggests.
In Vallejo, December is the coolest month, with average highs of 14°C (57°F) and humidity around 78% — considered high. In September, the warmest month, temperatures average 27°C (81°F) with 73% humidity — conditions that feel high. For a full picture, see our humidity page.
Climate temperature data is typically calculated as a 30-year average. This smooths out year-to-year variability and gives a more reliable picture of what a place is actually like, rather than what happened in any single unusual year.
The readings come from a range of sources — land-based weather stations, ocean buoys, ships, and satellites. That data is collected by weather services around the world, then pooled, quality-checked, and averaged to produce the climate records you see here.
For cities and regions with significant elevation, altitude is one of the biggest factors shaping local temperatures. As a rule of thumb, temperatures fall by around 6°C for every 1,000 metres gained — so a city at 2,000 metres will typically be around 12°C cooler than a city at sea level in the same region. Higher ground also tends to see more dramatic day-to-night temperature swings, since thinner air loses heat faster after sunset.
For more on Vallejo's weather — including monthly rainfall, sunshine hours, and humidity — visit our Vallejo climate page.
