Map from Google - Yosemite

The climate in the Yosemite National Park, located in California, along the mountain range of Sierra Nevada and about 250 kilometres (155 miles) east of San Francisco, varies mainly with altitude, and has significant temperature differences between night and day. In general, however, winter is cold, and summer is the sunniest and driest season.

Precipitation follows a Mediterranean pattern, therefore has a maximum in winter and a minimum in summer, especially at medium-low and medium altitudes, while at higher altitudes in summer some afternoon downpours or thunderstorms can break out. In quantity, precipitation varies with altitude and slope aspect: it generally increases with altitude, but it's also more abundant along the western slopes. At Yosemite Village, in the valley of the same name and at 1,200 metres (3,900 feet) of altitude, 930 millimetres (36.5 inches) of rain (or snow) per year fall, with a pronounced minimum in summer, when the rains are very rare. Here is the average precipitation.
Average precipitation - Yosemite Vill.
Yosemite Vill.JanFebMarAprMayJunJulAugSepOctNovDecYear
Prec. (mm)1651701307040151031555115140930

In the few areas located under 1,000 metres (3,300 feet), such as El Portal, a village located in a valley at 600 metres (2,000 feet) above sea level, winter is mild enough, given that the average temperature in January is 7.5 °C (45.5 °F), although it can get cold at night, with some night frosts; summer is hot and dry, with hot days, averaging around 33/34 °C (91/93 °F), but with peaks over 40 °C (104 °F). The rainfall in this secluded valley is scarce, around 290 mm (11.5 in) per year.
Here are the average temperatures in El Portal.
Average temperatures - El Portal
El PortalJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)356812141717141163
Max (°C)121518222731343331251712
Min (°F)374143465457636357524337
Max (°F)545964728188939188776354

Between 1,000 and 1,500 metres (3,300 and 4,900 feet), where there are the main towns, which are usually located in inland valleys, like Wawona, winter gets colder: during the night the temperatures often drop below freezing (0 °C or 32 °F), and heavy snowfalls are possible; the temperature can drop to -15/-20 °C in the worst moments. In summer, it's hot during the day, with highs often above 30 °C (86 °F), but the nights remain cool: the daily temperature range is remarkable. Sometimes in mid-summer there can be very hot days, with peaks of 40 °C (104 °F) and more, while in other situations at night the temperature can approach the freezing point.
Here are the average temperatures of Yosemite Village, situated at 1,200 metres (3,900 feet) above sea level.
Average temperatures - Yosemite Vill.
Yosemite Vill.JanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)-2-11371114131150-2
Max (°C)9111418222732322822138
Min (°F)283034374552575552413228
Max (°F)485257647281909082725546

At high altitudes, at about 2,000 metres (6,500 feet), winter is definitely cold, often snowy and frosty, and in summer it can be hot during the day, but the nights remain cool (or even cold).
Here are the average temperatures of Lee Vining, located east of the park, near Mono Lake, at 2,000 metres (6,500 feet) of altitude.
Average temperatures - Lee Vining
Lee ViningJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)-7-6-4-12610961-3-6
Max (°C)571015202529282419116
Min (°F)192125303643504843342721
Max (°F)414550596877848275665243

At even higher altitudes, winter gets really cold, with night temperatures several degrees below freezing and the coldest records about -30 °C (-22 °F), while summer is mild during the day and cold at night, with possible slight frosts even in July and August.
Here are the average temperatures at Ellery Lake, at almost 3,000 metres (9,800 ft) above sea level.
Average temperatures - Ellery Lake
Ellery LakeJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)-12-12-10-7-31652-2-7-10
Max (°C)224710152020161063
Min (°F)101014192734434136281914
Max (°F)363639455059686861504337

On the highest peaks, at around 4,000 metres (13,100 ft), there are glaciers along the north-facing slopes, like the Lyell Glacier and the Maclure Glacier. The highest peaks are located in the eastern part of the park, and are Mount Lyell, 3,997 metres (13,113 feet) high, and Mount Dana, 3,979 metres (13,054 feet) high.

Sequoia in Yosemite

When to go

The best time to visit the Yosemite National Park, is summer, from June to September. July and August are the warmest months, or the least cold at high altitudes. In June and September the temperature is lower by a few degrees, but there are also fewer tourists. Given that the temperatures vary depending on the altitude and the hour of day, it is advisable to dress in layers, to protect yourself from the sun (which in summer is very strong, especially in the mountains) with hat and sunglasses, but also from the cold of the night and of high altitudes, with warmer clothes.

Waterfalls are fed by the melting of the snow, so they reach their peak in spring and early summer, ie in May and June, and then decrease during the summer, and stay at a low level in autumn. In August, some waterfalls may be dry.

The streets located at higher elevations, such as the Tioga Road, which passes around 3,000 metres (9,800 ft) in the Tioga Pass, are usually opened in June, because until May they are impassable due to snow (although there are variations from year to year depending on the amount of snow).

Waterfall in Yosemite

In October the first snowfalls occur at high altitudes; then the snow line decreases gradually during autumn.
In winter the road in Yosemite Valley is open, but snow chains are often necessary. In this period you can explore the nature in silence, or even do skiing and cross country skiing in the Badger Pass Ski Area, one of the few ski areas within America's national parks.

Curiosity: to the east of Yosemite National Park, the landscape becomes semi-desert; not far away there is the ghost town of Bodie, at 2,500 metres (8,200 ft) above sea level, and Mono Lake, a very salty and alkaline lake, at 2,000 metres (6,500 feet) above sea level. Both are accessible from Tioga Road, when it is not closed due to snow (hence usually from June to September).