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Climate - United States West

Temperature, rainfall, prevailing weather conditions, when to go, what to pack

See also the US version (°F - inches - feet)

Flag - United States West

Map - United States West

1- West Coast (San Francisco, Los Angeles)
2- Deserts (Las Vegas, Phoenix)
3- Plateus (Salt Lake City, Grand Canyon)
4- Rocky Mountains

Coastal area

In the north-western states (Washington, Oregon), the weather is cool and rainy along the west coast and along the west-facing slopes, in cities like Seattle, Portland, Eugene. The average winter temperatures are about 3/5 °C, but every so often cold air masses coming from Alaska can arrive even here. Here are the average temperatures in Seattle.
Seattle average temperatures
Seattle J F M A M J J A S O N D
Min (°C) 3 3 4 6 9 11 13 13 11 8 4 2
Max (°C) 8 10 12 15 18 21 24 25 21 15 11 8

Rainfall is most abundant from November to January, and in any case is common for most of the year, except in summer: in July and August, the weather is pleasant and quite sunny, with cool nights and some morning fogs. In Seattle, there are about 2,000 hours of sunshine per year. If the rain is frequent, snow is rare: on average, 15 centimetres of snow per year fall. Here is the average precipitation.
Average precipitation Seattle
Seattle J F M A M J J A S O N D Year
Prec. (mm) 140 90 95 70 50 40 20 22 40 90 165 135 950
Days 18 15 17 14 12 9 5 5 8 13 18 18 152

At Seattle, the sea is cold all year, as can be seen in the following table.
Sea temperature Seattle
Seattle J F M A M J J A S O N D
Sea (°C) 8 8 8 10 12 13 14 14 13 11 9 8

Proceeding south, the west coast remains cool even in northern California, and even in San Francisco, but winter becomes progressively milder, and even cold spells become more rare.
In San Francisco and in the cities located in the bay of the same name, the climate is mild, rainy in the winter months, and sunny in the remainder of the year. Summer is particularly cool, often foggy in the morning, and the temperatures are similar to those of London. But luckily, in the late morning the sun comes out, and it usually shines for the rest of the day. Sometimes, however, even in San Francisco it can get hot, when the winds blow from inland.
San Francisco average temperatures
San Francisco J F M A M J J A S O N D
Min (°C) 5 6 7 8 10 11 12 12 12 10 8 6
Max (°C) 13 15 16 18 19 21 22 22 23 21 18 14

In San Francisco the sea is cold all year round, and its temperature varies little between winter and summer.
Sea temperature San Francisco
San Francisco J F M A M J J A S O N D
Sea (°C) 12 12 12 12 12 12 13 14 14 14 14 13

Continuing south along the coast of California, the temperature continues to rise, and the climate becomes milder, very pleasant, spring-like and sunny all year round, up to the border with Mexico. This happens because in the sea of California a cool current flows, making the climate mild and discouraging the formation of clouds, although it can generate some coastal fogs. But away from the coast, the summer heat quickly becomes more intense. For example, the Sacramento Valley has summer temperatures considerably higher than the coast: in July and August, the maxima in cities like Redding, Stockton, Fresno, Bakersfield are around 34/36 °C, while on the coast they do not go above 20 °C!
Going further south, in the Los Angeles area, the climate is pleasantly warm for most of the year: this is perhaps one of the finest climates in the world, even though it only applies to the coast and the surrounding areas. The maximum temperature in July is 24 °C in Santa Barbara (on the coast west of Los Angeles), while it rises to 28 °C already in downtown Los Angeles, to 33 °C in Pomona (40 kilometres to the east, in fact still in the Los Angeles conurbation, which is very extended), 36 °C in San Bernardino (45 kilometres more to the east), and even 42 °C in Palm Springs, 70 km to the south-east, already in full desert.
Here are the average temperatures of downtown Los Angeles.
Los Angeles average temperatures
Los Angeles J F M A M J J A S O N D
Min (°C) 9 10 11 12 14 16 18 18 17 15 11 9
Max (°C) 20 20 21 23 24 26 28 29 28 26 23 20

On the coast near Los Angeles, the sea is very cool in the summer, however, it reaches 18 °C in September.
Sea temperature Los Angeles
Los Angeles J F M A M J J A S O N D
Sea (°C) 14 14 14 14 14 15 17 17 18 17 16 15

In Los Angeles, the sunshine is guaranteed throughout the year, except during the brief periods of bad weather which can occur in winter: movies and television drama series filmed in Hollywood, in which the sun always shines, do not lie. It rains (not much) from mid-November to mid-April, and almost never in the rest of the year. In winter, the maximum temperatures are very mild, around 18/20 °C.

Los Angeles

The only disturbing element in the climate of this region is represented by the Santa Ana, a hot and very dry wind which can affect the coastal regions of Southern California. This wind is often accompanied by dust and is also capable of generating fires. More frequent in autumn and winter, it can show up in all seasons, and usually lasts a few days.
The islands off California (Channel Island, Santa Catalina, San Clemente, etc.) are very mild, sunny and semi-desert: in winter they are mild as the smaller islands of the Mediterranean, while in summer they are cool, with highs around 20 °C, and sometimes the sky is overcast because of the formation of cloud layers above the sea.

Deserts area
In the United States there are four desert areas, contiguous to each other. The northernmost is the Great Basin, an area that covers most of Nevada and western Utah, but having cold winters it will be discussed later, along with the highlands. Here, on the contrary, we will deal with the hot deserts.
As we have seen, about 150 kilometres south-east of Los Angeles, we find Palm Springs, a desert city, torrid in summer. The desert that extends through south-eastern California, southern Nevada and south-western Arizona is called Mojave Desert: the most typical type of desert, with the sunshine for most of the year, low rainfall, around 100 mm per year or less, concentrated in winter, and virtually absent in summer. The warmest areas of the desert are the valleys that lie around sea level or even below, such as Death Valley, a depression at 85 metres below sea level; these valleys have a mild winter, with highs around 18/20 °C and lows around 3/5 °C, and a long hot summer, with average highs around 42/46 °C. Death Valley is the hottest place in North America, and one of the hottest in the world: its highest recorded temperature is an incredible 57 °C!
At higher altitudes, the weather remains hot during summer, but it's more bearable, while winter nights can be cold. In Las Vegas, Nevada, at 650 metres above sea level, winter is mild during the day, around 13/15 °C, but with possible freezing cold at night. Snow is very rare, though the mountains surrounding the city are often covered with snow during winter. Summer is hot, with highs generally around 40 °C.
Las Vegas average temperatures
Las Vegas J F M A M J J A S O N D
Min (°C) 4 6 10 13 19 24 27 26 22 15 8 4
Max (°C) 14 17 21 26 32 37 40 39 34 27 19 14

Every so often, during summer some thunderstorms may break out, but for the rest the sun always shines. The sun is guaranteed in all seasons: in Las Vegas there are even 3,820 hours of sunshine per year, compared with 3,250 hours of the already sunny Los Angeles and 3,060 hours of San Francisco.

Las Vegas

Further south, between the south-eastern tip of California and the southwestern part of Arizona, we find the Sonoran Desert. Here the rainfall is slightly higher, between 100 and 250 mm per year, and it experiences a summer maximum, due to a bit of moist air coming from the Gulf of California, creating a kind of "little summer monsoon". This is the area where the saguaro, the giant cactus, is found. Let us make no mistake, the weather is still sunny for most of the year, but we cannot exclude some thunderstorms, sometimes even strong, in summer.
Phoenix, Arizona, at 340 metres above sea level, is located at the edge of the area. Here winter is mild, with cold nights but spring-like days, around 18/20 °C, while summer is scorchingly hot, around 40/42 °C during the day, and 26/27 °C at night. Phoenix is famous in the United States to be a very hot city. The sun always shines (even 3,876 hours a year), but in summer, from July to September, every so often a thunderstorm breaks out, and the wind can create sandstorms.
In Tucson, located further south, almost 800 metres above sea level, the peak of summer rainfall is even more visible: on average, 55 mm of rain fall in July, 60 mm in August and 30 mm in September. The maximum temperature is highest in June, 38 °C on average, while it drops slightly in July, to 37.5 °C, and in August to 36.5 °C, when, however, the relative humidity slightly increases.
Continuing east, in south-eastern Arizona, southern New Mexico and in the western part of Texas, we find the Chihuahuan Desert. Of course, the sun shines even here for most of the year, but the higher altitude, on average between 600 and 1,500 metres makes the climate cooler: during winter the minimum temperatures are around freezing or a few degrees below, while the maxima range between 15 °C and 18 °C, but sometimes during cold waves it may even snow; spring can be windy, and in summer the maxima hover around 35 °C. Here too there's a peak of rainfall in summer, between July and September, due to thunderstorm cells coming from the Gulf of California, which can sometimes cause floods. Two cities that are located in this climatic zone are El Paso, Texas, at 1,200 metres above sea level on the border with Mexico, and Roswell, New Mexico, at 1,100 metres. Here are the average temperatures in El Paso.
El Paso average temperatures
El Paso J F M A M J J A S O N D
Min (°C) -1 2 5 10 15 19 21 20 16 10 4 -1
Max (°C) 15 18 22 27 32 36 35 34 31 26 20 15

Rainfall in El Paso is scarce, around 250 millimetres per year, but you can notice the summer maximum. Here is the average rainfall.
Average precipitation El Paso
El Paso J F M A M J J A S O N D Year
Prec. (mm) 10 12 7 6 12 24 39 51 38 16 12 20 247
Days 4 3 2 2 3 4 8 9 6 5 3 4 53

East of the Pacific coast, two mountain ranges, both parallel to the coast, Cascade Range in the north and Sierra Nevada in the south, isolate the interior of the continent from maritime influences. East of these mountain chains we find the huge area of the Rocky Mountains, crossing the central-western United States from north to south. In addition to the highest peaks and ranges, there is a wide area of high altitude plateaus and valleys, where the climate features are quite similar: winter cold and summer heat; remarkable difference in temperature between night and day; low rainfall; limpid air; some summer thunderstorms; sudden increases in temperature due to the Chinook, the warm wind coming down from the mountains, which is able to melt the snow in a short time; intense cold waves in winter, with snowfall and strong northern winds.
Proceeding from north to south, at a given altitude, the climate becomes progressively warmer, to which must be added some differences (even as regards precipitation), depending on altitude and slope exposure. In general, the southern highlands are the driest, but there are areas of "rain shadow" even in the north.

Plateaus area

In the states of Washington and Oregon, which as we have seen have mild and rainy coasts, the bulk of precipitation coming from the ocean occurs in the mountain range known as Cascade Range.
To the east of this mountain range, there is an arid plateau, where the climate is continental, with wide temperature range between day and night. The total precipitation is scarce, though more abundant in winter, with possible heavy snowfalls. Strong waves of frost may occur in winter, and also some heat waves in summer; the latter are less frequent than in the centre-south. Spokane, Washington, 700 metres above sea level, lies in this area, and has an average temperature in January of -1,5 °C, and in July of 21 °C.
Spokane average temperatures
Spokane J F M A M J J A S O N D
Min (°C) -4 -3 0 3 7 10 14 13 9 3 -1 -5
Max (°C) 1 4 9 14 19 23 29 28 23 14 5 0

Precipitation in Spokane amounts to 420 mm per year, with a minimum in summer. On average, 1 metre and 17 centimetres of snow per year fall, and the snowy period runs from November to early April (of course it takes several centimetres of melted snow to have one cm of rain). Here is the average precipitation.
Average precipitation Spokane
Spokane J F M A M J J A S O N D Year
Prec. (mm) 46 34 41 33 41 32 16 15 17 30 58 58 421
Days 13 10 12 10 10 8 5 4 5 8 14 13 112

Further to the east, in Eureka, northern Montana, sitting at 920 metres above sea level, winter gets colder: the average in January is -5 °C, while in July it's 19.5 °C. Rainfall amounts to 375 mm, with a maximum due to afternoon thunderstorms in May and June. In a year, 125 cm of snow fall, from late October to April.
In the far north-east of California, in Alturas, at 1,300 metres above sea level, the average goes from -1 °C in January to 18 °C in July. In summer, the temperature range is truly remarkable: it goes from 7 °C at night to 31 °C during the day! Here the annual precipitation is 308 mm, with a minimum in summer. On average, 78 cm of snow per year fall.
Further to the north-east, in Boise, Idaho, at 865 metres above sea level, the average temperature goes from -1 °C in January to 24 °C in July, so summer begins to be quite hot. Here only 300 mm of rain per year fall, of which 53 cm of snow in the cold half of the year, with a minimum of rainfall in summer.
East of California, in Nevada, rainfall is very low, so that in general, this state is regarded as desert. But while cities such as Las Vegas have a warm climate, at higher altitudes the climate is steppic. It's the case of Reno, located at 1,350 metres in the north-west of the state, where the average temperature in January is 1.5 °C, and in July is 23 °C, but with wide temperature range, so that lows are 13 °C and highs 33 °C; the annual rainfall amounts to only 180 millimetres per year, with a minimum in summer. From November to April it can also snow, with a total of 62 cm of snow per year.
East of Nevada, in Utah, we find Salt Lake City, located at 1,300 metres above sea level, near the Great Salt Lake. Here the average temperature goes from -1.5 °C in January to 26 °C in July: summer is therefore hot, with some torrid days, and also sunny. The annual precipitation is not so scarce: 410 mm, with a maximum in spring and a minimum in summer. Between November and April, a lot of snow falls: a metre and a half on average. This city is located in a valley, and during winter, in periods of calm weather, accumulation of pollutants occurs, due to stagnation of cold air.
East of the city, there are snowy mountains, where the ski resort of Park City is found. Alta, at an elevation of 2,600 metres, is the second snowiest place in the United States, with its 13 metres of snow per year.

Salt Lake City

Let's now move to the north-east, in the state of Wyoming, where we find Cheyenne, at an altitude of even 1,872 metres, which has an average of -2 °C in January, and of 20.5 °C in July. Here, too, precipitation is around 400 mm per annum, with a maximum from May to August (mostly due to afternoon thunderstorms) and a minimum in winter. However, from late October to early May, snow falls (especially in March and April, when precipitation is higher than in winter), totalling 150 cm on average. Being this city on the eastern slope of the Rocky Mountains, the Chinook blows frequently, bringing warm and dry conditions. Hence, waves of frost can be intense but do not last long. The sun is frequent throughout the year.
South of Wyoming, in Colorado, we find Denver, which is located at 1,600 metres and has similar characteristics (sunshine, dry air, frequent Chinook, intense but short cold waves, wide temperature range between day and night), but it is a bit milder: the average in January is -0.5 °C, and that of July is 23 °C, but with cool or mild nights and hot or even torrid days.
Denver average temperatures
Denver J F M A M J J A S O N D
Min (°C) -8 -7 -3 1 6 11 15 14 9 3 -4 -8
Max (°C) 7 8 12 16 22 28 32 31 26 19 11 6

Even here precipitation is around 360 mm per year, with a summer maximum, still because of thunderstorms. Snow falls from October to April, and amounts to about 1 metre and 35 cm per year. The sun shines frequently, about 3,100 hours per year. Here is the average precipitation.
Average precipitation Denver
Denver J F M A M J J A S O N D Year
Prec. (mm) 10 9 23 43 54 50 55 43 24 26 16 9 363
Days 4 5 6 9 9 8 8 9 7 5 5 4 80


South of Colorado, we find New Mexico, whose main city, Albuquerque is located at 1,600 metres of altitude. Here we are at the edge of the Chihuahuan Desert, so that rainfall is scarce, 240 mm per year, with a maximum between July and September, due to the influence of the "little summer monsoon" that affects Arizona and New Mexico, and of which we have already spoken. Here is the average precipitation.
Average precipitation Albuquerque
Albuquerque J F M A M J J A S O N D Year
Prec. (mm) 10 12 15 16 13 17 38 40 27 26 15 13 240
Days 4 4 5 3 4 4 8 9 6 5 4 4 61

The January average is 2.5 °C, that of July is 26 °C. During winter, just 24 cm of snow fall. Spring is windy, with possible storms of sand and dust, and a little rainy. The sun shines for most of the year.
Albuquerque average temperatures
Albuquerque J F M A M J J A S O N D
Min (°C) -3 -1 2 6 11 16 19 18 14 8 1 -3
Max (°C) 8 11 16 21 26 31 32 31 27 21 13 8

Between Utah and Arizona, we find the Monument Valley, at 1,600 metres of altitude. Here winter is cold, with an average in January around freezing, and summer is warm, with hot days, given that highs are around 30/33 °C, and cool nights. The rainfall amount is practically desert, being lower than 200 mm per year, but at times thunderstorms can break out, which may take by surprise tourists, creating sudden streams in the valleys.

Monument Valley

In the Grand Canyon, Arizona, the climate varies with altitude. The south side is located at 2,100 metres above sea level, and has a cold and snowy winter (but there may also be periods of good weather, with sunshine during the day and freezing temperatures at night) and a warm summer, when days can be hot, but nights remain cool. Between July and September, some thunderstorms may break out in the afternoon, sometimes intense. The north side is located at an even higher altitude, around 2,400 metres, so it's even colder, and is covered by a coniferous forest. But at the bottom, inside the deep gorges where the river Colorado flows, about 700 metres above sea level, the climate is very different, and is similar to that of Las Vegas: hot and desert for many months, with mild winters.

Grand Canyon

In Arizona, above 2,000 metres, we find cities such as Flagstaff and Williams, which have a climate similar to the upper part (south side) of the Grand Canyon: the January average is around freezing, that of July is around 20 °C, snowfall may occur, sometimes heavy, in winter, while there's a lot of sunshine for most of the year, and some afternoon thunderstorms in summer.

We have already dealt with the mountain areas in which the climate is continental: here we will deal with the areas where the climate is definitely Alpine, due to the altitude.
As mentioned, in the state of Washington, the mild and moist Pacific currents discharge moisture on the western slopes of the Cascade Range. Mount Rainier is the snowiest place in the United States, with 17 metres of snow per year!
At the highest altitudes, above 2,000 metres, even in Arizona there are forests and ski resorts (such as the Apache National Forest and the Sunrise Park Resort).
The Yellowstone National Park, Wyoming, which has an average altitude of 2,400 metres, is cold for most of the year. The temperature remains below freezing for months, and snowfalls are abundant. The coldest records are spectacular, below -50 °C. In the summer months, the temperature is pleasant during the day, around 20/24 °C, but it's still cold at night (a few degrees above freezing). Precipitation, about 500 millimetres a year, is well distributed over the seasons, and occurs in the form of snow for several months a year. Here are the average temperatures.
Yellowstone average temperatures
Yellowstone J F M A M J J A S O N D
Min (°C) -18 -18 -15 0 -4 1 4 3 -1 -5 -11 -16
Max (°C) -5 -2 2 6 11 16 22 22 16 10 1 -4

In the Rocky Mountains, we find ski resorts like Vail and Aspen in Colorado, the aforementioned Park City, Utah, or those of the Sierra Nevada in California.


Speaking of Sierra Nevada, we can mention the Yosemite National Park, which has different climates depending on altitude: at higher altitudes (the highest peaks are almost 4,000 metres high) the climate is typically mountainous, while at medium-high altitudes, around 2,000 metres, the climate is that of the aforementioned plateaus (winter is cold and snowy, summer has warm days and cool nights, with some afternoon thunderstorms), while at the park entrances, around 1,200/1,500 metres above sea level, the climate is slightly milder: cold in winter, with rain and snow even abundant but also with some mild days, and warm and sunny in summer, when nights are still cool.
Here are the average temperatures of Yosemite Village, at an elevation of 1,200 metres.
Yosemite average temperatures
Yosemite J F M A M J J A S O N D
Min (°C) -2 -1 1 3 7 11 14 13 11 5 0 -2
Max (°C) 9 11 14 18 22 27 32 32 28 22 13 8

The rainfall in the park is much more abundant along the western side, and has a Mediterranean pattern, with a rainy (and snowy) season from mid-October to mid-May, and a dry summer.

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