California Mosquito Forecast

California stretches far enough north-to-south that its mosquito season isn't uniform. Areas near Chula Vista warm earlier and stay active longer, while cooler conditions up around Sacramento squeeze activity into the peak summer months. Pressure is on the lighter side overall, but local conditions, shown on the map above, decide any given day.

Tap any city on the map above, or open the full California map →

When is mosquito season in California?

California's mosquito season runs from April through October. Activity ramps up once overnight lows hold above about 50°F, and surges in the two to three days after rain, when fresh standing water triggers a new hatch. Long dry spells keep a lid on numbers between rain events. The season also shifts within the state, running earlier and longer toward Chula Vista and shorter and later up around Sacramento.

Where are mosquitoes worst in California?

Within California, the most consistent pressure tends to land around Los Angeles, San Diego, and San Jose. In a dry state, the standing water mosquitoes need is concentrated in cities (irrigation, lawns, retention ponds, stormwater), so the metros read higher than the open country around them. Anywhere near rivers, marshes, lakes, or recent flooding will read higher than the surrounding area, exactly the kind of local detail the live map above is built to show.

How the California forecast works

MosquitoCast estimates California's mosquito activity from live weather (temperature, humidity, wind, and recent rainfall) layered on the area's long-term rainfall climate, elevation, and terrain, and refreshed every day from NOAA's forecast data. It's the same model nationwide, so the reading for California is directly comparable to anywhere else in the country.