CONTENTS:
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. Average winter temperatures are about 3/5 °C (37/41 °F), but every so often cold air masses coming from Alaska can arrive here. Here are the average temperatures in Seattle.
Average temperatures - Seattle
SeattleJanFebMarAprMayJunJulAugSepOctNovDec
SeattleJFMAMJJASOND
Min (°C)3346911131311842
Max (°C)8101215182124252115118
Min (°F)373739434852555552463936
Max (°F)465054596470757770595246

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. While rain is frequent, snow is rare: on average, 15 centimetres (6 inches) of snow per year fall. Here is the average precipitation.
Average precipitation - Seattle
SeattleJanFebMarAprMayJunJulAugSepOctNovDecYear
SeattleJFMAMJJASONDY
Prec. (mm)140909570504020224090165135950
Prec.(in)5.53.53.72.821.60.80.91.63.56.55.337.4
Days18151714129558131818152

At Seattle, the sea is cold all year round, as can be seen in the following table.
Sea temperature - Seattle
SeattleJanFebMarAprMayJunJulAugSepOctNovDec
SeattleJFMAMJJASOND
Sea (°C)8881012131414131198
Sea (°F)464646505455575755524846

Proceeding south, the west coast remains cool even in northern California, and down to 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 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 wind blows from inland.
Average temperatures - San Francisco
San FranciscoJanFebMarAprMayJunJulAugSepOctNovDec
San FranciscoJFMAMJJASOND
Min (°C)567810111212121086
Max (°C)131516181921222223211814
Min (°F)414345465052545454504643
Max (°F)555961646670727273706457

In San Francisco the sea is cold all year round, and its temperature varies little between winter and summer.
Sea temperature - San Francisco
San FranciscoJanFebMarAprMayJunJulAugSepOctNovDec
San FranciscoJFMAMJJASOND
Sea (°C)121212121212131414141413
Sea (°F)545454545454555757575755

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, down to the border with Mexico. This happens because along the coast of California a cool current flows, making the climate mild and hindering the formation of clouds, although it can generate some coastal fogs. But away from the coast, in summer the heat becomes more intense. For example, in the Sacramento Valley the summer temperatures are considerably higher than in the coast: in July and August, highs in cities like Redding, Stockton, Fresno, Bakersfield are around 32/34 °C (93/97 °F), while on the coast they do not go above 20 °C (68 °F)!
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 (75 °F) in Santa Barbara (on the coast to the west of Los Angeles); it rises to 28 °C (82 °F) already in downtown Los Angeles, to 33 °C (91 °F) in Pomona, 40 kilometres (25 miles) to the east, in fact still in the Los Angeles conurbation, which is very extended, to 36 °C (97 °F) in San Bernardino, 45 kilometres (30 miles) more to the east, and to as high as 42 °C (108 °F) in Palm Springs, 70 km (45 miles) to the south-east, and located in the desert.
Here are the average temperatures of downtown Los Angeles.
Average temperatures - Los Angeles
Los AngelesJanFebMarAprMayJunJulAugSepOctNovDec
Los AngelesJFMAMJJASOND
Min (°C)9101112141618181715119
Max (°C)202021232426282928262320
Min (°F)485052545761646463595248
Max (°F)686870737579828482797368

On the coast near Los Angeles, the sea is very cool even in summer, however, it reaches 18 °C (64 °F) in September.
Sea temperature - Los Angeles
Los AngelesJanFebMarAprMayJunJulAugSepOctNovDec
Los AngelesJFMAMJJASOND
Sea (°C)141414141415171718171615
Sea (°F)575757575759636364636159

In Los Angeles, the sun shines 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 (64/68 °F).

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 occur 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 as mild as the smaller islands of the Mediterranean, while in summer they are cool, with highs around 20 °C (68 °F), although in this season sometimes the sky is overcast, because cloud banks can form over 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 (95 miles) 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: this is the most typical type of desert, with sunshine for most of the year, low rainfall, around 100 mm (4 in) 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 (280 feet) below sea level; these valleys have a mild winter, with highs around 18/20 °C (64/68 °F) and lows around 3/5 °C (37/41 °F), and a long torrid summer, with average highs around 42/46 °C (108/115 °F). Death Valley is the hottest place in North America, and one of the hottest in the world: here the highest recorded temperature is an incredible 56.7 °C (134 °F)!
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 (2,100 ft) above sea level, winter is mild during the day, around 13/15 °C (55/59 °F), but with possible slight frosts at night. Snow is very rare, though in winter the mountains surrounding the city are often covered with snow. Summer is hot, with highs generally around 40 °C (104 °F).
Average temperatures - Las Vegas
Las VegasJanFebMarAprMayJunJulAugSepOctNovDec
Las VegasJFMAMJJASOND
Min (°C)46101319242726221584
Max (°C)141721263237403934271914
Min (°F)394350556675817972594639
Max (°F)57637079909910410293816657

Every so often, during summer some thunderstorms may break out, but for the rest the sun always shines: in Las Vegas there are even 3,820 hours of sunshine per year, more than in Los Angeles (3,250 hours), and in San Francisco (3,060 hours).

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 (4 and 10 in) per year, and it experiences a summer maximum, due to a bit of moist air coming from the Gulf of California, which creates a kind of "little summer monsoon". This is the area where the saguaro, the giant cactus, is found. Let there be 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 (1,100 feet) 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 (64/68 °F), while summer is scorchingly hot, around 40/42 °C (104/108 °F) during the day, and 26/27 °C (79/81 °F) at night. Phoenix is famous in the United States for being a very hot city. The sun almost always shines (even 3,876 hours per year), but in summer, from July to September, every so often a thunderstorm breaks out, and the wind can cause sandstorms.
In Tucson, located further south, almost 800 metres (2,600 feet) above sea level, the peak of summer rainfall is even more visible: on average, 55 mm (2.2 in) of rain fall in July, 60 mm (2.4 in) in August and 30 mm (1.2 in) in September. The maximum temperature is highest in June, 38 °C (100 °F) on average, while later it drops slightly, to 37.5 °C (99.5 °F) in July, and to 36.5 °C (97.5 °F) in August, when, however, relative humidity slightly increases.
Continuing east, in south-eastern Arizona, in 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 (2,00 and 5,000 feet) makes the climate cooler: in winter, lows are around freezing (0 °C or 32 °F) or a few degrees below, while highs range between 15 °C and 18 °C (59 and 64 °F), but sometimes during cold waves it may even snow; spring can be windy, and in summer highs hover around 35 °C (95 °F). 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 (3,900 feet) above sea level on the border with Mexico, and Roswell, New Mexico, at 1,100 metres (3,600 feet). Here are the average temperatures in El Paso.
Average temperatures - El Paso
El PasoJanFebMarAprMayJunJulAugSepOctNovDec
El PasoJFMAMJJASOND
Min (°C)-125101519212016104-1
Max (°C)151822273236353431262015
Min (°F)303641505966706861503930
Max (°F)596472819097959388796859

Rainfall in El Paso is scarce, around 250 millimetres (10 inches) per year, but you can notice the summer maximum. Here is the average rainfall.
Average precipitation - El Paso
El PasoJanFebMarAprMayJunJulAugSepOctNovDecYear
El PasoJFMAMJJASONDY
Prec. (mm)1012761225405040151220247
Prec.(in)0.40.50.30.20.511.621.60.60.50.89.7
Days43223489653453


East of the Pacific coast, two mountain ranges, both parallel to the coast, the Cascade Range in the north and the 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, which cross the central-western United States from north to south. In addition to the highest peaks and ranges, there is a wide area of plateaus and high altitude valleys, where the climate features are quite similar: winter cold and summer heat; remarkable difference in temperature between night and day; low precipitation; 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 snowfalls and strong northern winds.
Proceeding from north to south, at a given altitude, the climate becomes progressively warmer, while there are also some local differences (even as regards precipitation), depending on altitude and slope exposure. In general, the southern highlands are the driest, but there are "rain shadow" areas even in the north.

Plateaus area

In the states of Washington and Oregon, which as we have seen are mild and rainy along the coast, the bulk of precipitation coming from the ocean is released on the 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. Total precipitation is scarce, though is 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 (2,300 feet) above sea level, lies in this area, and has an average temperature in January of -1,5 °C, and in July of 21 °C (70 °F).
Average temperatures - Spokane
SpokaneJanFebMarAprMayJunJulAugSepOctNovDec
SpokaneJFMAMJJASOND
Min (°C)-4-303710141393-1-5
Max (°C)1491419232928231450
Min (°F)252732374550575548373023
Max (°F)343948576673848273574132

Precipitation in Spokane amounts to 420 mm (16.5 in) per year, with a minimum in summer. On average, 1 metre and 17 centimetres (46 inches) 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, and the same applies to inches). Here is the average precipitation.
Average precipitation - Spokane
SpokaneJanFebMarAprMayJunJulAugSepOctNovDecYear
SpokaneJFMAMJJASONDY
Prec. (mm)453540354030151515306060420
Prec.(in)1.81.41.61.41.61.20.60.60.61.22.42.416.5
Days1310121010854581413112

Further to the east, in Eureka, northern Montana, located at 920 metres (3,020 feet) above sea level, winter is colder: the average in January is -5 °C (23 °F), while in July it's 19.5 °C (67 °F). Precipitation amounts to 375 mm (14.5 in), with a maximum due to afternoon thunderstorms in May and June. In a year, 125 cm (50 in) of snow fall, from late October to April.
In the far north-east of California, in Alturas, at 1,300 metres (4,250 feet) above sea level, the average goes from -1°C (30 °F) in January, to 18 °C (64 °F) in July. In summer, the temperature range is truly remarkable: it goes from 7 °C (44.5 °F) at night to 31 °C (88 °F) during the day! Here the annual precipitation is 308 mm (12 in), with a minimum in summer. On average, 78 cm (30.7 in) of snow per year fall.
Further to the north-east, in Boise, Idaho, at 865 metres (2,840 feet) above sea level, the average temperature goes from -1°C (30 °F) in January, to 24 °C (75 °F) in July, so summer begins to be quite hot. Here only 300 mm (12 in) of rain per year fall, of which 53 cm (21 in) 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 we find a steppe climate. It's the case of Reno, located at 1,350 metres in the north-west of the state, where the average temperature of January is 1.5 °C (34.5 °F), and that of July is 23 °C (73 °F), but with wide temperature range, so that lows are around 13 °C (55.5 °F) and highs around 33 °C (91 °F); annual precipitation amounts to only 180 millimetres (7 inches) per year, with a minimum in summer. From November to April it can snow, with a total of 62 cm (24.5 in) of snow per year.
East of Nevada, in Utah, we find Salt Lake City, located at 1,300 metres (4,250 feet) above sea level, near the Great Salt Lake. Here the average temperature goes from -1.5 °C (29.5 °F) in January to 26 °C (79 °F) in July: therefore summer is hot, with some torrid days, and also sunny. Annual precipitation is not so scarce: 410 mm (16 in), with a maximum in spring and a minimum in summer. Between November and April, a lot of snow falls: a metre and a half (60 in) on average. This city is located in a valley, and during winter, in periods of calm weather, pollutants accumulate in the air, due to cold air stagnation.
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 (8,500 ft), is the second snowiest place in the United States, with its 13 metres (42.5 feet) of snow per year.

Salt Lake City

Let us now move to the north-east, in the state of Wyoming, where we find Cheyenne, at an altitude of as high as 1,870 metres (6,135 feet), which has an average of -2 °C (28 °F) in January, and of 20.5 °C (69 °F) in July. Here, too, precipitation is around 400 mm (16 in) 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 (60 in) 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 frequently shines throughout the year.
South of Wyoming, in Colorado, we find Denver, which is located at 1,600 metres (5,250 feet) 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 of January is -0.5 °C (31 °F), and that of July is 23 °C (73 °F), but with cool or mild nights and hot or even torrid days.
Average temperatures - Denver
DenverJanFebMarAprMayJunJulAugSepOctNovDec
DenverJFMAMJJASOND
Min (°C)-8-7-31611151493-4-8
Max (°C)781216222832312619116
Min (°F)181927344352595748372518
Max (°F)454654617282908879665243

Even here precipitation is around 360 mm (14 in) 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 (53 in) per year. The sun shines frequently, totalling about 3,100 hours per year. Here is the average precipitation.
Average precipitation - Denver
DenverJanFebMarAprMayJunJulAugSepOctNovDecYear
DenverJFMAMJJASONDY
Prec. (mm)101025455550554525251510365
Prec.(in)0.40.411.82.222.21.8110.60.414.4
Days45699889755480

Denver

South of Colorado, we find New Mexico, whose main city, Albuquerque is located at 1,600 metres (5,250 feet) of altitude. Here we are at the edge of the Chihuahuan Desert, so that rainfall is scarce, 240 mm (9.5 in) per year, with a maximum between July and September, due to the influence of the "little summer monsoon", which affects Arizona and New Mexico, and of which we have already spoken. Here is the average precipitation.
Average precipitation - Albuquerque
AlbuquerqueJanFebMarAprMayJunJulAugSepOctNovDecYear
AlbuquerqueJFMAMJJASONDY
Prec. (mm)101015151515404025251515240
Prec.(in)0.40.40.60.60.60.61.61.6110.60.69.4
Days44534489654461

The average of January is 2.5 °C (36.5 °F), that of July is 26 °C (79 °F). During winter, only 24 cm (9.5 in) of snow fall. Spring is windy, with possible storms of sand and dust, with little rainfall. The sun shines for most of the year.
Average temperatures - Albuquerque
AlbuquerqueJanFebMarAprMayJunJulAugSepOctNovDec
AlbuquerqueJFMAMJJASOND
Min (°C)-3-126111619181481-3
Max (°C)8111621263132312721138
Min (°F)273036435261666457463427
Max (°F)465261707988908881705546

Between Utah and Arizona, we find the Monument Valley, at 1,600 metres (5,250 feet) 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 (8 in) per year, but at times thunderstorms can break out, which may take tourists by surprise, 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 (6,900 ft) 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 (7,900 ft), 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 (2,300 feet) above sea level, the climate is very different, and is similar to that of Las Vegas: desert, and torrid for many months, with mild winters.

Grand Canyon

In Arizona, above 2,000 metres (6,500 feet), we find cities such as Flagstaff and Williams, which have a climate similar to the upper part (south side) of the Grand Canyon: the average of January is around freezing, that of July is around 20 °C (68 °F); snowfalls 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 (55 feet) of snow per year!
At the highest altitudes, above 2,000 metres (6,500 feet), 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 (7,900 ft), 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 (-58 °F). In the summer months, the temperature is pleasant during the day, around 20/24 °C (68/75 °F), but it's still cold at night (a few degrees above freezing). Precipitation, about 500 millimetres (20 inches) per year, is well distributed over the seasons, and occurs in the form of snow for several months. Here are the average temperatures.
Average temperatures - Yellowstone
YellowstoneJanFebMarAprMayJunJulAugSepOctNovDec
YellowstoneJFMAMJJASOND
Min (°C)-18-18-150-4143-1-5-11-16
Max (°C)-5-2261116222216101-4
Min (°F)00532253439373023123
Max (°F)232836435261727261503425

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.

Aspen

As regards Sierra Nevada, we can mention the Yosemite National Park, which has different climates depending on altitude: at higher altitudes (the highest peaks are around 4,000 metres or 13,100 feet high) the climate is typically mountainous, while at medium-high altitudes, around 2,000 metres (6,500 feet), the climate is that of the aforementioned plateaus (winter is cold and snowy, summer has hot days and cool nights, with some afternoon thunderstorms), while at the park entrances, around 1,200/1,500 metres (3,900/4,900 ft) above sea level, the climate is slightly milder: cold in winter, with rain and snow even abundant but also with some mild days, and hot and sunny in summer, when nights are still cool.
Here are the average temperatures of Yosemite Village, at an elevation of 1,200 metres (3,900 feet).
Average temperatures - Yosemite
YosemiteJanFebMarAprMayJunJulAugSepOctNovDec
YosemiteJFMAMJJASOND
Min (°C)-2-11371114131150-2
Max (°C)9111418222732322822138
Min (°F)283034374552575552413228
Max (°F)485257647281909082725546

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


See also:
United States Centre and East.
Alaska
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