Modesto has a Warm Bsh climate classification. It has mild winters with moderate rainfall and long, hot, dry summers. Average January temperatures range from 56 °F (13 °C) in the day to 40 °F (4 °C) at night. Most of the rainfall occurs during the winter and the annual total is 13.2 in (340 mm). The city does not have a full storm sewer system, and many streets flood during winter rain storms.
Average July temperatures range from 95 °F (35 °C) in the day to 63 °F (17 °C) at night. During the summer months there can be multiple days in a row with high temperatures exceeding 100 °F (38 °C). This can pose health risks for people with weak constitutions or who ignore the dangers of heat stroke. Onshore breezes (known locally as the “delta breeze”) moderate these high temperatures somewhat, with cooler air coming in after 8 or 9 pm on summer nights.