Spring is the prime time. From late February through April the almond orchards around Modesto come into bloom, an unforgettable sight if you have not seen the sea of pink and white blossom that covers the valley. April and May have warm but not yet brutal afternoons.
Summer is hot — daytime highs of 35–40°C (95–105°F) from late June through early September are normal. The dry heat is bearable in shade and at the pool, but sightseeing outside is best confined to mornings and evenings. Autumn through the harvest months of September and October is good for farm-stand visits and the wine-country day trips into the Sierra foothills.
Winter is mild and damp. The Central Valley fog — tule fog — can blanket the area for days at a time from December into February and is dense enough to close highways. Plan inside-activities and avoid driving at night during the worst of it.