Climate - United States

Index

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• Introduction
• West Coast - Seattle, San Francisco, Los Angeles
• Deserts - Las Vegas, El Paso
• Plateaus - Denver
• Rocky Mountains - Yellowstone
• Center-east: continental climate - Duluth, Fargo, Chicago
• Center-east: semi-continental climate - Cincinnati, New York, Boston, Washington
• Center-east: warm temperate climate - Dallas, Atlanta
• Center-east: Gulf of Mexico and Florida - Houston, Orlando, Miami
• Center-east: hurricanes
• Center-east: tornadoes

Introduction

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Being a huge country, the contiguous United States is home to a wide variety of climates. However, in general it has a continental climate, with cold winters (often frigid) and hot summers (sometimes very hot), with a different season duration depending on latitude and distance from the sea. There are, however, some exceptions: on the west coast overlooking the Pacific Ocean, the climate is cool and damp in the northern part and Mediterranean in the southern part; on the coast of the Gulf of Mexico, the climate is mild in winter and hot and muggy in summer, while in Florida, it is almost tropical; the mountainous areas are cold in winter and cool to cold even in summer; and finally, there are deserts which are mild in winter and scorchingly hot in summer.
Since there are no obstacles to cold air masses from Canada, almost all of the country can experience sudden cold waves in winter, but they have different intensity and duration depending on area. Cold spells last a few days in the south, where the temperature drops a few degrees below freezing (0 °C or 32 °F) in winter, while they are intense and sometimes long in inland areas, in the highlands and in the north-east. Heat waves in summer can be intense as well, especially in inland areas. In general, the western half of the country is more arid than the eastern one, with the exception of the north-central coast of the Pacific, which is rainy.
While the Western United States are mostly occupied by mountains and plateaus, with vast arid and desert areas, the central-eastern part is mostly flat or covered by hills and low mountains, and its climate is generally more humid and rainy. Given the vastness of the territory, the climatic differences are remarkable here as well.
In the central-eastern part, clashes of air masses are remarkable and frequent, making the climate unstable in most of the territory, and meteorological phenomena may be violent (storms, hail, blizzards, tornadoes). Air masses coming from Canada are cold and dry (but pick up moisture when passing over the Great Lakes), while those from the Gulf of Mexico are warm and moist.
The Great Plains experience higher temperature variations, but are also less humid and rainy than the East Coast, especially in winter.

West Coast

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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, and Eugene. Average temperatures in winter are about 3/5 °C (37/41 °F), but every so often, cold air masses from Alaska can arrive here.
Here are the average temperatures in Seattle, located in the northwest, in the state of Washington, 150 km (90 mi) south of the Canadian border.

Rainfall is most abundant from November to January, though it's common for most of the year, except in summer. In fact, in July and August, the weather is pleasant and quite sunny, with cool nights and some morning fogs. While rain in Seattle is frequent, snow is rare: on average, 15 centimeters (6 inches) of snow fall per year. Here is the average precipitation.

Near Seattle, the sea is cold all year round, and ranges from 8 °C (46.5 °F) in January to 13.5 °C (56 °F) in August.
Proceeding south, the west coast remains cool even in northern California and down to San Francisco, but winter becomes progressively milder, and cold spells become rarer.
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, the sun comes out in late morning, and it usually shines for the rest of the day. Sometimes, however, it can get hot even in San Francisco, when the wind blows from inland.

Near San Francisco too, the sea is cold all year round, in fact its temperature reaches a maximum of 14/14.5 °C (57/58 °F) from August to October.
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 a cool current flows along the coast of California, which is able to make the climate mild and to hinder rain cloud formation, although it can generate low clouds and coastal fogs. But away from the coast, the heat in summer is more intense. For example, the summer temperatures are considerably higher in the Sacramento Valley than on the coast: in July and August, highs in cities like Redding, Stockton, Fresno, Bakersfield are around 35/37 °C (95/99 °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. In winter, the maximum temperatures are very mild, around 20/21 °C (69/71 °F). In July, the average maximum temperature is 23.5 °C (74.5 °F) in Santa Barbara (on the coast to the west of Los Angeles) and it's already 29 °C (84 °F) in downtown Los Angeles, while 40 kilometers (25 miles) to the east, in Pomona, still in the Los Angeles conurbation (which is very extended), it reaches 33 °C (91 °F). In San Bernardino, 45 km (30 mi) more to the east, the average reaches 36 °C (97 °F), while in Palm Springs, 70 km (45 miles) to the south-east, and located in the desert, it is as high as 42 °C (108 °F).
Here are the average temperatures of downtown Los Angeles.

On the coast near Los Angeles, the sea is very cool even in summer, however, it reaches 18.5 °C (65 °F) in August and September.

In Los Angeles, the sun shines throughout the year, except during the short periods of bad weather which can occur in winter: movies and tv series filmed in Hollywood, where 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.

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 it's 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 the coas of California (Channel Islands) 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 22 °C (72 °F). In addition, owing to the cool current, cloud banks can form above the sea in summer, so the sky can be overcast.

South of Los Angeles, and near the border with Mexico, we find San Diego, where the climate is similar to that of the L.A. coast.

The deserts

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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 since it has cold winters, it will be discussed later, along with the highlands. Here, on the contrary, we will talk about the hot deserts.
As previously mentioned, about 150 kilometers (95 miles) south-east of Los Angeles, we find Palm Springs, a desert city, scorchingly hot 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 hottest areas of the desert are the valleys that lie around sea level or even below, such as Death Valley, a depression at 85 meters (280 feet) below sea level. Here, there's a mild winter, with highs around 19/20 °C (66/68 °F) and lows around 5 °C (41 °F), and a long, scorching summer, with average highs around 42/47 °C (108/117 °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 54.4 °C (130 °F)!
At higher altitudes, the weather remains hot in summer, but it's more bearable, while winter nights can be cold. In Las Vegas, Nevada, at 650 meters (2,100 ft) above sea level, winter is mild during the day, around 14/15 °C (57/59 °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).

Every so often, a thunderstorm may break out during summer, but for the rest, the sun almost always shines: in Las Vegas, there are as many as 3,820 hours of sunshine per year, even 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 there's a maximum in summer due to 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 meters (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 40/41 °C (105/107 °F) during the day. Phoenix is famous in the United States for being a very hot city. The sun almost always shines (up to 3,875 hours per year), but in summer, from July to September, every so often, a thunderstorm can break out, and the wind can cause sandstorms.
In Tucson, Arizona, located further south, at almost 800 meters (2,600 feet) above sea level, the peak of the rainfall in summer is even more evident: on average, 55 mm (2.2 in) of rain fall in July, 50 mm (2 in) in August and 35 mm (1.4 in) in September. The maximum temperature is highest in June, 38.5 °C (101 °F) on average, while later it drops slightly, to 38 °C (100 °F) in July and to 37 °C (99 °F) in August, when, however, the humidity slightly increases.
Continuing east, in south-eastern Arizona, southern New Mexico and the westernmost 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 meters (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 can even snow; spring can be windy, and in summer, highs hover around 35 °C (95 °F). Here, too, there's a peak in the 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 meters (3,900 feet) above sea level on the border with Mexico, and Roswell, New Mexico, at 1,100 meters (3,600 feet).
Here are the average temperatures in El Paso.

Rainfall in El Paso is scarce, around 225 millimeters (9 inches) per year, but you can notice the maximum in summer. Here is the average rainfall.

The plateaus

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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 valleys at high altitude, where the climatic characteristics 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, the climate becomes progressively warmer, while there are also some local differences (as regards to precipitation as well) depending on altitude and slope exposure. In general, the southern highlands are the driest, but there are "rain shadow" areas also in the north.



In the states of Washington and Oregon, which, as we said before, 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 it 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 center-south.
In this area we find the cities of Spokane (located in the state of Washington), Eureka (Montana), Alturas (California), Boise (Idaho), Reno, (Nevada).
East of Nevada, in Utah, we find Salt Lake City, located at 1,300 meters (4,250 feet) above sea level, near the Great Salt Lake. Here, the average temperature ranges from -0.5 °C (31.5 °F) in January to 27.5 °C (81 °F) in July; therefore, summer is hot, with some scorching days, and also sunny.

Annual precipitation is not so scarce: 395 mm (15.5 in), with a maximum in spring and a minimum in summer. Between November and April, a lot of snow falls: 145 cm (55 in) on average. This city is located in a valley, and during winter, in periods of calm weather, pollutants accumulate in the air because of 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 meters (8,500 ft), is the second snowiest place in the United States, with its 13 meters (42.5 feet) of snow per year.



North-east of Utah, in the state of Wyoming we find Cheyenne, at an altitude of as high as 1,870 meters (6,135 feet), where the average temperature ranges from -2 °C (28 °F) in December to 21 °C (70 °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 that this city lies 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 meters (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 monthly average temperature ranges from -0.5 °C (31 °F) in December to 24 °C (75 °F) in July, when, however, nights are mild to cool and days are hot and sometimes scorching.
South of Colorado, we find New Mexico, whose largest city, Albuquerque is located at 1,600 meters (5,250 feet) of altitude. Here, we are at the edge of the Chihuahuan Desert, in fact, rainfall is scarce, 225 mm (9 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.
Between Utah and Arizona, we find the Monument Valley, at 1,600 meters (5,250 feet) of altitude. Here, winter is cold, with an average in January around freezing. In contrast, summer is hot during the day, with maximum temperatures around 30/33 °C (86/91 °F), and cool nights. Precipitation is practically at desert levels, in fact, it is 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.



In the Grand Canyon, Arizona, the climate varies with altitude. The south side is located at 2,100 meters (6,900 ft) above sea level, and has cold, snowy winters (but there may also be periods of good weather, with sunshine during the day and freezing temperatures at night) and warm summers, 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 meters (7,900 ft), so it's even colder, and it's covered by a coniferous forest. But at the bottom, inside the deep gorges where the river Colorado flows, about 700 meters (2,300 feet) above sea level, the climate is very different, and it is similar to that of Las Vegas: desert and scorchingly hot for many months, with mild winters.



In Arizona, above 2,000 meters (6,500 feet), we find cities such as Flagstaff and Williams, where the climate is similar to the upper part (south side) of the Grand Canyon: the average temperature is around freezing in January and around 20 °C (68 °F) in July; snowfalls can occur, sometimes heavy, in winter, while there's a lot of sunshine for most of the year, and some afternoon thunderstorms in summer.

Rocky Mountains

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We have already talked about the parts of the mountain areas in which the climate is continental: here, we will talk about the areas where there is a cold mountain climate (Alpine) because of the altitude.
As mentioned, in the state of Washington, the mild Pacific currents release moisture as precipitation on the western slopes of the Cascade Range. Mount Rainier is the snowiest place in the United States, with 17 meters (55 feet) of snow per year!
At the highest altitudes, above 2,000 meters (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 meters (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 millimeters (20 inches) per year, is evenly spread over the seasons, and occurs in the form of snow for several months. Here are the average temperatures in Yellowstone Lake.

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



As regards to the Sierra Nevada, we can mention the Yosemite National Park, which has different climates depending on altitude, and the Sequoia National Park.

Center-east: continental climate

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The central-eastern part of the United States where the climate is continental can be divided into two.
In the northernmost part (which includes the northernmost part of Montana, North Dakota, Minnesota, Wisconsin and Michigan, the north-east of the state of New York, and the northern part of Vermont, New Hampshire and Maine), the climate is continental with long, cold, snowy winters and moderately warm summers. The average daily temperature in January is several degrees below freezing, from -15 °C (5 °F) to -5 °C (23 °F), while in July, it doesn't reach 20 °C (68 °F). Summer is a fairly rainy season because of afternoon thunderstorms in the west, and also because of the weather disturbances that can affect the areas of the Great Lakes and the east. However, the sun frequently shines. During summer, intense heat waves can occur, with peaks above 35 °C (95 °F), but they only last a few days.
Here are the average temperatures in Duluth (Minnesota). As you can see, the summer is not very warm.

In Duluth, precipitation amounts to 790 millimeters (31 inches) per year, with a minimum in winter, when there are frequent snowfalls, though generally not abundant, and a maximum in summer. Near Duluth, Lake Superior approaches the freezing point in winter (but on colder winters, a thick layer of ice forms), while in summer, although it warms up considerably, it remains very cool, if not cold, for swimming.
In this area, precipitation is fairly scarce in the western part, where it's inferior to 500 millimeters (20 inches) per year, mainly because of the relatively dry winter, while it's more abundant in the Great Lakes region and in the north-east. As a consequence, snowfalls (which typically occur from late October to mid-April) are relatively less abundant in the west, where they amount to about 70 cm (27.5 in) per year in North Dakota, while they are definitely abundant around the Great Lakes and in the north-east: typically, they range from 150 to 250 cm (60 to 100 in), but they can even surpass 3 meters (120 in) in the Upper Peninsula.
In the area of the Great Lakes, winter snowfalls are more abundant along the coasts exposed to the north and west (because of a phenomenon called lake-effect snow, whereby cold winds, initially dry, pick up moisture over the lakes, and bring snowfall on the leeward shores). In Houghton, northern Michigan, on the shores of Lake Superior, snowfall amounts to 5 meters and 30 cm (208 inches) per year; in L'Anse, a little more to the south and 500 meters (1,600 feet) above sea level, it almost reaches 6 meters (20 feet) per year!
In the northeast, Mount Washington New Hampshire, 1,917 meters (6,289 feet) high, is constantly affected by disturbances generated by the clash between warm and cold air masses, and receives no less than 7 meters (23 feet) of snow per year.
Being that the climate of this area is inhospitable, no large cities are found.



More to the south (in the band which in the southern part extends to the north of Nebraska, Iowa, Illinois, Indiana, Ohio, Pennsylvania, Connecticut and Massachusetts), the climate is still continental: winter is still cold and snowy, but summer is warm to hot, with averages in July equal to or higher than 20 °C (68 °F). During summer, thunderstorms can occur in the afternoon, though they are generally less intense and frequent than in the central and southern regions. Winter temperatures are very low: the average in January hovers between -15 °C and -3 °C (5 and 27 °F).
Here too, the western part, that of the Great Plains, is more arid than the central and eastern part.
During winter, cold air outbreaks from Canada are accompanied by furious gusts of blizzard, and the temperature can drop below -30 °C (-22 °F). Snowy landscapes and sub-freezing temperatures even during the day are the norm for weeks.
Snowfall is more abundant in the Great Lakes area and in the east, where it ranges from 150 to 250 cm (60 to 100 in) per year, while it drops below 1 meter (3.3 feet) in the westernmost states (Montana, North and South Dakota).
During summer, there may be intense heat waves, with higher temperature but lower humidity in the west, where highs can exceed 40 °C (104 °F), and more sultry and uncomfortable heat in the Great Lakes and in the east; anyway, they generally last a few days.
In Fargo, North Dakota, the average in January is -12.7 °C (9.1 °F), like in northern Sweden. The temperature drops below -18 °C (0 °F) for 50 days a year on average. Summer is warm: the average in July is 21.5 °C (70.5 °F), although nights remain typically cool. Precipitation amounts to 610 mm (24 in) per year, with a minimum in winter and a maximum in early summer due to afternoon thunderstorms. Snowfall amounts to 130 cm (51 in) per year. Here is the average temperatures.

With an average January temperature of -9 °C (16 °F), Minneapolis, Minnesota, is colder than Moscow, Russia. In a typical year, from November to April, 130 cm (50 in) of snow fall. In the worst periods, the temperature can plunge to -35 °C (-31 °F). On the other hand, summer is quite hot: the average in July is 23.5 °C (74.5 °F). Precipitation, about 805 mm (31.5 in), is scarcer in winter and more abundant in summer, when it occurs mainly in the form of thunderstorm.
Further south, in Des Moines, Iowa, the average temperature ranges from -5.3 °C (22.5 °F) in January to 24.5 °C (76 °F) in July. On average, 94 cm (37 in) of snow fall each year.
On the coast of Lake Michigan, Chicago, known as the "Windy City", has cold winters, with freezing periods due to outbreaks of cold air from the Canadian Arctic region, but also some milder periods. The average in January is -3 °C (26.5 °F), but the temperature drops below -18 °C (0 °F) for an average of 4 nights per year. Snowfall amounts to about one meter (40 in) per year. Summers are warm to hot and humid, with thunderstorms in the afternoon, and also with possible heat waves. The daily average in July is 25 °C (77 °F). During summer, the temperature exceeds 32 °C (90 °F) for 21 days on average.

The climate of cities such as Indianapolis (Indiana), Detroit (Michigan) and Cleveland (Ohio), is similar to that of Chicago.
The coast of the state of New York overlooking Lake Erie and Lake Ontario has similar temperatures, but it's particularly snowy on account of the aforementioned lake-effect snow. In Buffalo, nearly 2 meters (6.5 feet) of snow fall per year. The temperatures are similar to those of Chicago, but summer is a bit less hot because of the cooling effect of the lake, which here is more evident. The Niagara Falls, a few kilometers (or miles) away from Buffalo, also belong to this climate zone.
Along the east coast, in Portland, Maine, the average ranges from -4.5 °C (24 °F) in January to 21.5 °C (70.5 °F) in July. Annual precipitation is abundant, and amounts to 1,200 mm (47 in), well distributed throughout the year, though with a relative minimum in summer. Here, 175 cm (69 in) of snow fall per year.

Center-east: semi-continental climate

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In this band (which includes Kansas, the north of Oklahoma, Arkansas and Tennessee, Missouri, the south of Illinois and Indiana, Kentucky, West Virginia, the south of Pennsylvania and New York, New Jersey, Delaware, Massachusetts, Connecticut, Rhode Island, Virginia, and District of Columbia), the climate is continental, but is more forgiving in winter, while it becomes definitely hot in summer. Winter is still cold, with an average in January ranging from -3 °C to 4 °C (26.5 to 39 °F); there can be cold waves, but they alternate with mild periods. Summer is hot and sunny, especially in the western part, while it's a bit milder in the area of the Appalachian Mountains and along the east coast. Summer is a fairly rainy season, mainly because of afternoon thunderstorms, but in the central and eastern part, some weather fronts may also pass. In summer, heat waves can occur, sometimes intense, and unlike in the north of the country, they can be persistent.

In this area, several large cities are found.

Kansas City is located in the Great Plains of the Midwest, near the geometric center of the United States. Here, winter is cold, and the average in January is -0.5 °C (31 °F). Summer is definitely hot, with an average in July of 27 °C (81 °F), and muggy too. The amount of sunshine is great: 2,800 hours per year. Precipitation amounts to 1,000 mm (40 in) per year, and it's most abundant in late spring and summer, when it often occurs in the form of thunderstorm. On average, 28 cm (11 in) of snow fall per year.
Further east, the climate of St. Louis (Missouri) and Cincinnati (Ohio) is similar to that of Kansas City.
Here is average temperature in Cincinnati.

Here is the average precipitation in Cincinnati.

The Appalachian Mountains are very snowy in winter, at least on the north-western slopes: snowfall is abundant especially on the north-facing elevations of West Virginia, where it amounts to about 150 cm (60 in) per year, and it's less abundant on those of Virginia, where it amounts to 50 cm (20 in) per year. The altitude tempers a bit the summer heat in the cities located at low-mountain elevations.

On the east coast, the proximity to the sea makes the climate a bit more temperate, but it must be said that the prevailing currents come from inland, so the climate is still continental.
New York, despite being on the coast and at a relatively low latitude, 41° north, has a cold winter: the average in January is 0.8 °C (33.4 °F). Summer is hot and muggy, and the average in July is 25.3 °C (77.5 °F). The climate is perpetually unstable, in fact all kinds of weather may occur: clear or overcast, windy or calm, cold or warm, even within the same week.
Further to the north-east, Boston (Massachusetts), is a bit colder and snowier in winter: the average in January is -1 °C (30 °F), the annual amount of snow is 125 cm (49 in), and snow storms can be even worse than in New York. On the other hand, summer is a little milder: the average in July is 23.5 °C (74 °F). The sea is colder, and fog can sometimes occur in spring, while in summer, sea breezes are often effective in tempering the heat. Here too, heat waves may occur in summer, and there are frequent thunderstorms in the afternoon, sometimes accompanied by hail.
In fact, Boston is at the limit of this climate zone: moving further to the north or to the interior, we enter the previous area, the colder one of the north.
South of New York, Washington, the federal capital, is instead a bit warmer than the Big Apple: the average ranges from 3 °C (37.5 °F) in January to 27 °C (81 °F) in July.

Center-east: warm temperate climate

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In this belt (which includes southern Oklahoma, north-central Texas, south-central Arkansas, southern Tennessee, and most of the states of Mississippi, Alabama, Georgia, and North Carolina), winter is mild, in fact the average temperature in January is between 4 °C and 9 °C (39 and 48 °F). However, short waves of frost are possible even at these latitudes. In the north of this band, 15/20 cm (6/8 in) of snow still fall per year, while in the south, the snowfall average drops to about a few centimeters per year, which means that sometimes, it never snows for an entire winter (or maybe, more than one).
Summer, is long, hot and muggy, tropical-like, with afternoon thunderstorms, sometimes intense, especially in the central and eastern part. Oklahoma and north-central Texas are often oppressively hot, with an annoying combination of moisture and high temperature: highs range between 34 °C and 36 °C (93/97 °F), but they can remain around 40 °C (104 °F) for weeks. Further east, temperatures are a bit lower, in fact, highs are usually around 32/33 °C (90/91 °F), but relative humidity is even higher. After all, we are at the latitude of northern Africa, but south of this area, instead of the Sahara, there is the Gulf of Mexico, from which warm, moist air masses often arrive.
Precipitation drops below 1,000 mm (40 in) per year in the western area (Texas, Oklahoma), while it's quite abundant in the central-eastern part, where it reaches about 1,200/1,300 mm (47/51 in) per year. Spring is a very rainy season because of the conflict between air masses coming from the north, which are still cold, and subtropical air masses lying in the south. In spring, tornadoes may also occur (see below).
At this latitude, the westernmost part of Texas belongs to the Chihuahuan Desert, of which we have previously spoken.
In Dallas, the average temperature ranges from 7.7 °C (45.9 °F) in January to 30.2 °C (86.4 °F) in July. In winter, the weather is often mild, with highs about 15/20 °C (59/68 °F), but there are also sudden cold waves, usually of short duration, when the temperature can drop to a few degrees below freezing. In winter rainfall is not abundant, and snowfall is rare: on average, 6 cm (2.4 in) of snow fall each year. Summer is long and oppressive, very difficult to bear, with some afternoon thunderstorms. There are as many as 100 days per year with maximum temperatures above 32 °C (90 °F). The weather is pleasant in spring and autumn, although strong thunderstorms and even tornadoes may sometimes occur in spring, and more rarely in autumn.

In Dallas, the annual precipitation amounts to 940 mm (37 in). Here is the average precipitation.



In Memphis, Tennessee, the average temperature ranges from 5.5 °C (42 °F) in January to 28 °C (82 °F) in July. Here, too, winter is mild, but there can be some short and intense waves of frost, accompanied with snow; on average, 12 cm (4.7 in) of snow fall per year. Rainfall, much more abundant than in Dallas, amounts to 1,400 mm (55 in) per year, with a relative minimum between August and October. Thunderstorms are possible throughout the year; in summer, they are generally short-lived, while in spring, they can be intense, and accompanied with wind gusts.
In Atlanta, Georgia, the slightly higher altitude, about 300 meters (1,000 feet), temper a little the summer heat: the average temperature ranges from 7 °C (44.5 °F) in January to 26.8 °C (80 °F) in July. The rains are abundant here as well, amounting to 1,280 mm (50.5 in) per year, and are well distributed throughout the year.

Gulf of Mexico and Florida

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In this region comprising the area bordering the Gulf of Mexico, the climate is sub-tropical, and it's warm and humid for many months of the year. Winter is very mild, since the averages in January are higher than 9 °C (48 °F). But even here, in spite of the southern location, cold spells in winter can sometimes occur, though quite rarely; the southern part of Florida is the most sheltered and is almost always spared from the cold, to the point of having an almost tropical climate.
Here too, the western part is less humid: precipitation drops below 1,000 mm (40 in) only in south-western Texas, while starting from eastern Texas, this whole band is rainy and with plenty of thunderstorms.
The amount of sunshine is not exceptional, in fact, in the long summer season, although the sun still prevails, clouds can form in the afternoon, and can cause thunderstorms, while some tropical low pressure systems can also pass over the area.
In this area, in the month of October, and sometimes November, there's a relative lull in precipitation, with calm and pleasant days (if it is not affected by the last hurricanes of the season).

In Austin and San Antonio (Texas), the weather in winter is usually very mild, but with possible short cold waves: however, the average in January is around 10 °C (50 °F), and in the rest of the year, the temperature is similar to that of Dallas, with an equally very hot and humid summer, while tornadoes in spring are less frequent because of the greater proximity to the sea.

In the south-western tip of Texas, from Corpus Christi to the Mexican border, the winter is very mild, since highs are around 20 °C (68 °F) even in January, and the rainfall is not abundant, since it hovers between 500 and 800 mm (20 and 30 in) per year.
Houston is located about 50 kilometers (30 miles) away from the sea (but Galveston Bay borders the southeastern districts of the city): here, the average temperature ranges from 12 °C (53.5 °F) in January to 29.5 °C (85 °F) in July, when highs are around 35 °C (95 °F) and the humidity is high. It's no surprise that a city so uncomfortably hot has been the first in the world to see a widespread distribution of air conditioners. Rainfall amounts to 1,315 mm (52 in) per year, so it's fairly abundant, and well distributed throughout the year.
In New Orleans, Louisiana, the summer temperatures are similar to those of Houston, but the omnipresence of water makes the heat even more sweltering. The rains are definitely abundant: up to 1,610 mm (63 in) per year.

Near New Orleans, the Gulf of Mexico is warm enough for swimming from May to November, and it gets very warm in the summer months. In winter, it is a bit cold, since it drops to 18 °C (64 °F).

In peninsular Florida, winter is even milder, and spring-like.
In Orlando and Tampa, the January average is around 16 °C (61 °F). There are tropical weather conditions from mid-May to September, with heat, humidity and frequent thunderstorms. April and October are hot but a little drier.
Here are the average temperatures in Orlando.

However, it's the southern part of Florida, which is a true winter refuge for many American snowbirds.
In Miami, on the southern tip of the state and near the Tropic of Cancer, the January average is 20 °C (68 °F), so here there is no winter: the sun often shines, the air is pleasantly warm, and a nice breeze blows from the sea.

Hurricanes

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The states on the Gulf of Mexico (Texas, Louisiana, Mississippi, Alabama, and Florida) as well as the southernmost Atlantic states (Georgia, North and South Carolina) can be affected by tropical depressions and hurricanes, which occasionally can also affect other Atlantic coastal states. The areas most at risk are the coastal ones, however, hurricanes can also penetrate inland, even though, in these cases, they tend to weaken. The hurricane season runs from June to November, although they are most likely from August to October.

Tornadoes

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Another danger comes from tornadoes, which are large and intense whirlwinds. Tornadoes are very rare in the western part of the United States (the states of the Pacific, the Rocky Mountains and the deserts) and are typical of the central and eastern states, except the northern portions of the states of the Great Lakes and of the northeast. However, tornadoes are more frequent in the central-southern states, except on the coasts. They develop mainly along two lines: the "Tornado Alley", from South Dakota to northern Texas (north/south direction), and the "Dixie Alley", from Oklahoma to Ohio (south-west/north-east direction).
The months when they are most frequent are May and June, but they may also occur between February and April, especially in the south, while in summer, they can occur in the northern part of the Great Plains.
In Florida, tornadoes are quite frequent, but they are generally less intense than on the mainland.

Other resources available for the climate of the United States and of overseas possessions:

American Samoa (Oceania)
Hawaii (Oceania)
Puerto Rico (Caribbean)
United States Virgin Islands (Caribbean)



When to go and what to pack in United States