If the Western United States
are occupied mostly 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.
Clashes of air masses
are large and frequent, making the climate unstable in most of the territory, also with violent phenomena (storms, hail, blizzards, tornadoes). Cold air masses coming from Canada are cold and dry (but pick up moisture when passing over the Great Lakes), those from the Gulf of Mexico are warm and moist.
We divided the territory into four bands, substantially parallel, and within each of them the climate is fairly uniform, although the westernmost part, that of the Great Plains, experiences higher temperature jumps, and is also less humid and rainy than the eastern part, especially in winter.
In this northernmost part (which includes the northernmost part of Montana, North Dakota, Minnesota, Wisconsin, Michigan, the north-east of the state of New York, and northern Vermont, New Hampshire and Maine), the climate is continental
with long, cold, and 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 for the passages of weather disturbances in the area of the Great Lakes and in the east; however, the amount of sunshine is good. During summer, intense heat waves can occur, with peaks above 35 °C (95 °F), but they last a few days.
Here are the average temperatures of Duluth (Minnesota).
Average temperatures - Duluth
In Duluth, precipitation amounts to 775 millimetres (30.5 inches) per year, with a winter minimum, when there are frequent but generally not abundant snowfalls, and a summer maximum. Here is the average precipitation.
Average precipitation - Duluth
At Duluth, Lake Superior approaches the freezing point in winter (but during colder winters, a thick layer of ice forms), while in summer, although it warms considerably, stays very cool, if not cold, for swimming.
Lake temperature - Duluth
In this area, precipitation is fairly scarce in the western part, where less than 500 millimetres (20 inches) per year fall, mainly because of the relatively dry winter, while it becomes 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 even more than 3 metres (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 (due to a phenomenon called lake-effect snow
: cold winds, initially dry, pick up moisture moving across the lakes and bring snowfall on the leeward shores). In Houghton, northern Michigan, on the shores of Lake Superior, 4 metres of snow per year fall; in L'Anse, a little more to the south and 500 metres (1,600 feet) above sea level, snowfall amounts to almost 6 metres (20 feet) per year!
In the Northeast, Mount Washington, in New Hampshire, 1,917 metres (6,289 feet) high, is constantly affected by disturbances generated by clashes of warm and cold air masses, and receives no less than 7 metres of snow per year.
Being the climate of this area inhospitable, no large cities are found.
In this band (which in the southern part extends to the north of Nebraska, Iowa, Illinois, Indiana, Ohio, Pennsylvania, Connecticut and Massachusetts), the climate is continental
: winter is still cold and snowy, but summer is by now warm or even hot, with averages of July equal to or greater than 20 °C (68 °F). During summer, afternoon thunderstorms can occur, which are, however, 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 outbreaks from Canada are accompanied by furious gusts of blizzard, and the temperature can drop to 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 metre in the westernmost states (Montana, North and South Dakota).
During summer, there may be intense heat waves, with higher temperatures but lower humidity in the west, where it 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.
, North Dakota, the average in January is -12.7 °C (9.1 °F), like in the north of Sweden. The temperature drops below -18 °C (0 °F) for fifty days a year on average. Summer is warm: the average in July is 21.5 °C (70.5 °F), although the nights remain typically cool.
Average temperatures - Fargo
In Fargo, precipitation amounts to 570 mm (22.5 in) per year, with a winter minimum and a maximum on early summer, due to afternoon thunderstorms. Snowfall amounts to 130 cm (50 in) per year. Here is the average precipitation.
Average precipitation - Fargo
With an average January temperature of -9 °C (16 °F), Minneapolis
, Minnesota, in winter 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 drop to -40 °C (-40 °F). On the other hand, summer is hot: the average in July is 23 °C (73 °F). Precipitation, about 770 mm (30 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 goes 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 a frigid winter, with outbreaks of cold air from the Canadian Arctic region, and humid and hot summers, with thunderstorms in the afternoon, and also with possible heat waves. The average in January is -4.5 °C (24 °F), but the temperature drops below -18 °C (0 °F) for an average of 6 nights per year. Snowfall amounts to about one metre per year. The daily average in July is 23.5 °C (74.5 °F). During summer, the temperature exceeds 32 °C (90 °F) for 21 days on average.
Average temperatures - Chicago
In Chicago, 940 mm (37 in) of rain or snow per year fall, with a relative minimum in winter and a summer maximum. Here is the average precipitation.
Average precipitation - Chicago
At Chicago, Lake Michigan is very cold in winter, while in summer it's still cool, but becomes almost acceptable for swimming, at least in August, or for those who do not suffer from the cold.
Lake temperature - Chicago
The climate of cities like 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 Ontario has a similar temperature, but it's particularly snowy, due to the aforementioned lake-effect snow. In Buffalo
, nearly 2 metres of snow per year fall. 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 kilometres (or miles) from Buffalo, also belong to this climate zone.
Along the east coast, the average in Portland
(Maine), goes from -5 °C (23 °F) in January, to 20.5 °C (69 °F) in July. The annual precipitation is abundant and amounts to 1,200 mm (47 in), well distributed throughout the year (with a relative minimum in summer). Here, 160 cm (63 in) of snow per year fall.
In this band (which includes Kansas, 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, District of Columbia), the climate is continental, but is more forgiving in winter, while it becomes quite 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 waves of cold, but they alternate with mild periods. Summer is hot and sunny, especially in the western part, while it becomes a bit milder in the area of the Appalachian Mountains and along the east coast. Summer is a fairly rainy season too, because of afternoon thunderstorms, but in the central and eastern part, some weather fronts may also pass. In summer, heat waves can occur, even intense, and unlike in the north of the country, they can sometimes be persistent.
(The north-western part of Texas, where lies Amarillo, lies in the highlands, of which we have dealt with in the page about the western United States.)
In this area, several large cities are found.
is located in the Great Plains of the Midwest, near the geometric centre of the United States; here winter is cold, so that the average in January is -0.8 °C (30.6 °F); summer is definitely hot, in fact the average in July is 27.3 °C (81.1 °F), and muggy too. The amount of sunshine is great: 2,800 hours per year. The rainfall amounts to 1,000 mm (40 in) per year, and is most abundant in late spring and summer, when it occurs often in the form of thunderstorm. On average, 50 cm (20 in) of snow per year fall.
Further east, the climate of St. Louis
(Missouri) and Cincinnati
(Ohio) is similar to that of Kansas City.
Average temperatures - Cincinnati
Here is the average precipitation in Cincinnati.
Average precipitation - Cincinnati
The Appalachian Mountains
are very snowy in winter, at least on the north-western slopes: snowfall is abundant especially on the north-facing hills of West Virginia, when it amounts to about 150 cm (60 in) per year, and less abundant on those of Virginia, when it amounts to 50 cm (20 in) per year, while the altitude temper a bit the summer heat in the cities located on the hills.
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.
, despite being on the coast and at a relatively low latitude, of 40° north, has a cold winter: the average in January is 0.5 °C (33 °F), while summer is hot and muggy, as the average of July is 24.5 °C (76 °F); the climate is perpetually unstable
, therefore all kinds of weather may occur: clear or overcast, windy or calm, cold or warm, even within the same week. In the middle of winter, there can be mild days, Mediterranean-like, with about 15.5 °C (60 °F), but the cold wind from the northwest can rapidly lower the temperature, and maybe bring snowfall, in a few hours. On average, 68 cm (27 in) of snow per year fall, from December to March (but sometimes also on early April or late November). Rainfall is abundant: about 1,200 mm (47 in) each year, well distributed throughout the seasons; in summer they often take place in the form of thunderstorms. Despite this, the amount of sunshine is good. In winter, the city can experience snow storms and waves of frost, with low around -10/-15 °C (5/14 °F), while in summer, masses of warm, moist air from the Gulf of Mexico can make the heat uncomfortable.
Average temperatures - New York
In New York, the sea is very cold in winter, while in summer it is a bit cool, but all in all you can swim in July and August, and those who do not suffer from the cold can try to swim also in September.
Sea temperature - New York
Further to the north-east, Boston
(Massachusetts), is a bit colder and more snowy in winter: the average in January is -1.5 °C (29.5 °F), the annual amount of snow is 114 cm (45 in), and snow storms can be even worse than in New York. On the other hand, here summer is a little milder: the average in July is 23 °C (73 °F). The sea is colder, so that in spring sometimes fogs occur, while in summer the sea breezes are often effective in tempering the heat. Here too heat waves may occur in summer, and even here 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 inland, we enter in the previous area, the colder zone of the north.
South of New York, Washington
, the federal capital, is instead a bit warmer than the Big Apple: the average in January rises to 2.3 °C (36.1 °F), and in July to 26.6 °C (79 °F). Waves of frost and snow in winter are still possible, but they are a bit rarer: on average, 40 cm (16 in) of snow per year fall, but big snowfalls and winter storms occur only once every three or four years. Summer is hot and humid, with fewer breaks than in New York and Boston: here an annoying and sticky heat dominates, and it can last for weeks. Fortunately, even here there's no shortage of afternoon thunderstorms, which can break the heat at least for a few hours.
In this belt (which includes southern Oklahoma, north-central Texas, south-central Arkansas, southern Tennessee, and most of Mississippi, Alabama, Georgia and North Carolina), winter is mild
, given that 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, still 15/20 cm (6/8 in) of snow per year fall, while in the south, the snowfall average drops to about a few centimetres per year, which means that sometimes it never snows for an entire (or maybe more than one) winter.
, is long, hot and muggy
, tropical-like, with afternoon thunderstorms, sometimes intense, especially on the east-central 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 often reach 40 °C (104 °F) for weeks, and the humidity is quite high, at least for those temperatures. Further east, the temperatures are a bit lower, with maximum temperatures usually around 32/33 °C (90/91 °F), but the 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 and moist air masses often arrive.
Rainfall drops below 1,000 mm (40 in) per year in the western area (Texas, Oklahoma), while it becomes 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. October is typically a calmer month, with little rain, after the summer thunderstorms and before the return of autumn and winter rains.
At this latitude, the westernmost part of Texas is part of the Chihuahuan Desert, of which we've talked about in the page about the western United States.
Now, let's see in detail the climate of some cities.
, the average temperature goes 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), alternating with sudden cold waves, usually short, in which the temperature can drop a few degrees below freezing. The winter rains are not abundant, and snowfall is rare: on average, 6 cm (2.4 in) of snow fall each year. Summer is long and sultry, very difficult to bear, with some afternoon thunderstorms. There are as many as 100 days in a 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.
Average temperatures - Dallas
In Dallas, the annual precipitation amounts to 920 mm (36 in). Here is the average precipitation.
Average precipitation - Dallas
, Tennessee, the average temperature goes between 5 °C (41 °F) in January and 28 °C (82 °F) in July. Here, too, winter is mild, but it's possible to see short and intense waves of frost, accompanied by snow; on average, 12 cm (4.7 in) of snow per year fall. Rainfall, much more abundant than in Dallas, amounts to 1,360 mm (53.5 in) per year, with a relative minimum between August and October. Thunderstorms are possible throughout the year; in summer they are generally short, while in spring they can be intense, and accompanied by wind gusts.
, Georgia, the slightly higher altitude, about 300 metres (1,000 feet), temper a little the summer heat: the average temperature is between 6.5 °C (43.5 °F) in January and 26.8 °C (80 °F) in July. Even here the rains are abundant, amounting to 1,260 mm (49.5 in) per year, and are well distributed throughout the year, but being usually intense and short-lived, they do not decrease the sunshine duration by much.
Average temperatures - Atlanta
In this region, which includes 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, sometimes cold spells in winter may 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 from eastern Texas to the far east, this whole band is rainy and with plenty of thunderstorms.
The sunshine amount is not exceptional, because in the long summer season, although the sun still prevails, clouds can form in the afternoon, associated with thunderstorms, and even the passage of some tropical low pressure systems must be put into account.
Even in this belt, October, and sometimes November, experience 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), in winter the weather is usually very mild, but with possible short waves of cold or frost: however, the average in January is around 10 °C (50 °F), for the rest of the year the temperature is similar to that of Dallas, with an equally hot and humid summer, while spring tornadoes are less frequent, for the greater proximity to the sea.
The south-western tip of Texas, from Corpus Christi to the mexican border, has a semi-arid climate, therefore it's different from the rest of the area, which is very rainy. Here the wettest period is from May to October (with a break in July); the rainiest month is September.
, which is located about 50 kilometres (30 miles) away from the sea, the average temperature goes from 11.5 °C (52.5 °F) in January, to 29.3 °C (84.5 °F) in July, when highs are around 34/35 °C (93/95 °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.
Average temperatures - Houston
In Houston, rainfall amounts to 1,260 mm (49.5 in) per year, so it's fairly abundant, and well distributed throughout the year. Here is the average precipitation.
Average precipitation - Houston
At Houston, 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 cool but not cold, since it doesn't drop below 19 °C (66 °F) in February.
Sea temperature - Houston
In New Orleans
, Louisiana, the summer temperatures are slightly lower than in Houston, but the omnipresence of water makes the heat even heavier. The rains are definitely abundant: even 1,575 mm (62 in) per year.
In peninsular Florida
, winter is even milder, and spring-like. In Orlando
, the January average is around 15/16 °C (59/61 °F). The climate is tropical-like from mid-May to September, with heat, humidity and frequent thunderstorms. April and October are hot, but a little drier.
Average temperatures - Orlando
In Orlando, 1,300 mm (51 in) of rain per year fall, but already at this latitude you notice the minimum in winter, due to the less frequent weather fronts, and the definite maximum in summer, due to thunderstorms. Here is the average rainfall.
Average precipitation - Orlando
But it's the southern part of Florida, that is a true winter refuge for many Americans. In Miami
, on the southern tip of the state and near the Tropic of Cancer, the January average is 20 °C (68 °F), therefore here there is no winter: the sun often shines, the air is pleasantly warm, and a nice breeze blows from the sea. Very different, however, is the climate in the long hot summer, which is still sunny, but rainy as well, with frequent thunderstorms, at times strong. The rainiest period goes from May to mid-October. The heat is sweltering, even though the annoyance is partially reduced by the breeze. Winter is instead quite dry, however, there are still 5/6 days with rain per month.
Average temperatures - Miami
In Miami, the sea is warm enough for swimming all year round, since the water temperature in winter is 24 °C (75 °F); in summer, the sea is very warm for many months.
Sea temperature - Miami
Between late summer and early autumn, the coasts of the Gulf of Mexico and the southern 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 hurricane season runs from June to November, although they are most likely from mid-August to late September.
Another danger comes from tornadoes
, large and dangerous whirlwinds, which are very rare in the western part of the United States (the states of the Pacific and the Rocky Mountains, see the page of the Western United States), and are typical of the central and eastern states we are dealing with here, except the northern portions of the states of the Great Lakes and of the northeast. However, tornadoes are more frequent in the south-central band (zones 3 and 4), except on the coast. 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 in which they are most frequent are from 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.
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