Which part of California? It's a big place, with forests, coastal scrub, lowland deserts, mountains, highland deserts.
Tourists to California mostly stay in coastal areas. Within 5 miles of the coast, the temperatures will be very nice in May, June. Daytime highs about 20-22 deg. C. Nighttime lows about 15-16 deg. C in the south, and a little colder in the North.
From about 10 miles inland and before you hit mountains: greater temperature fluctuations than in coastal areas, but still quite pleasant.
Mountains: about the same as described above in the south, but colder as you go north.
Deserts: much hotter in the day, and a bit colder at night. Cooler again at night, in the highland deserts (north of Death Valley), and hotter during the day in Death Valley itself.
One thing to be aware of about the coastal areas in May-June... you may not get much sunshine. SoCal locals call this "April gloom followed by May doom". There's a strong inversion layer leading to low level clouds near the coast this time of year. Residents may not see the sun at all from about late March to mid June -- or even later.
Conversely, especially in the south, you just might get a Santa Ana -- hot easterly winds and lots of sunshine.
Tourists to California mostly stay in coastal areas. Within 5 miles of the coast, the temperatures will be very nice in May, June. Daytime highs about 20-22 deg. C. Nighttime lows about 15-16 deg. C in the south, and a little colder in the North.
From about 10 miles inland and before you hit mountains: greater temperature fluctuations than in coastal areas, but still quite pleasant.
Mountains: about the same as described above in the south, but colder as you go north.
Deserts: much hotter in the day, and a bit colder at night. Cooler again at night, in the highland deserts (north of Death Valley), and hotter during the day in Death Valley itself.
One thing to be aware of about the coastal areas in May-June... you may not get much sunshine. SoCal locals call this "April gloom followed by May doom". There's a strong inversion layer leading to low level clouds near the coast this time of year. Residents may not see the sun at all from about late March to mid June -- or even later.
Conversely, especially in the south, you just might get a Santa Ana -- hot easterly winds and lots of sunshine.