The Climate of Illinois describes the weather conditions, and extremes, noted within the state of Illinois, United States, over time.
Because of its nearly 400-mile (640 km) length and mid-continental location, Illinois has a widely varying climate. Most of Illinois has a humid continental climate (Köppen climate classification Dfa) with hot, humid summers and cool to cold winters. However, the southern half of the state, from about Springfield southward, has a humid subtropical climate (Köppen Cfa) with winters becoming more moderate as one travels south. Average yearly precipitation for Illinois varies from 48 inches or 1,220 mm at the southern tip to 35 inches or 890 mm in the northern portion of the state. Normal annual snowfall exceeds 38 inches or 0.97 m in Chicago, while the southern portion of the state normally receives less than 14 inches or 0.36 m. [1] The highest temperature recorded in Illinois was 117 °F (47.2 °C), recorded on July 14, 1954, at East St. Louis, while the lowest temperature was −38 °F (−38.9 °C), recorded on January 31, 2019, at Mount Carroll.
Illinois averages around 50 days of thunderstorm activity a year which put it somewhat above average for number of thunderstorm days for the United States. Illinois is vulnerable to tornadoes with an average of 54 occurring annually, which puts much of the state at around 9.7 tornadoes per 10,000 square miles (30,000 km2) annually. [2] [3] The deadliest tornado on record in the nation occurred largely in Illinois. The Tri-State Tornado of 1925 killed 695 people in three states; 613 of the victims lived in Illinois. [4]
Due to the urban heat island effect, cities tend to be 2 °F or 1.1 °C warmer on average, which is most noticeable overnight. [5]
The 1995 Chicago heat wave was one of the worst weather-related disasters in state history, with 525 dead within a five-day period as overnight lows remained as high as 84 °F (28.9 °C) and daytime highs reached up to 106 °F (41.1 °C). [6] The most deadly heatwave in the history of the United States struck Illinois during July 1936, which killed 2,656 people. [7]
Extreme temperature changes can occur within minutes with the passage of a strong cold front through the state. On December 20, 1836, temperatures fell 40 °F or 22.2 °C in minutes, which supposedly froze people to their saddles and chickens in their tracks. [8] Until 2019, the lowest temperature was −37 °F (−38.3 °C), recorded on January 15, 2009, at Rochelle. [9] However, Illinois did not officially recognize this measurement, as it was made from a small airport and there were no quality control procedures applied to the measurement. [10] As a result, the official record-lowest temperature for the state was −36 °F (−37.8 °C) recorded at Congerville on 5 January 1999. [11] In 2019, the January North American Cold Wave struck Illinois. This resulted in a new record low temperature, −38 °F (−38.9 °C), recorded on January 31, 2019, at Mount Carroll.
City | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Cairo [12] | 41/25 | 47/29 | 57/39 | 69/50 | 77/58 | 86/67 | 90/72 | 88/69 | 81/61 | 71/49 | 57/39 | 46/30 |
Chicago [13] | 31/16 | 35/20 | 47/29 | 59/39 | 70/48 | 80/58 | 84/64 | 82/63 | 75/54 | 62/43 | 48/32 | 35/21 |
Edwardsville [14] | 36/19 | 42/24 | 52/34 | 64/45 | 75/55 | 84/64 | 85/59 | 86/66 | 79/58 | 68/46 | 53/35 | 41/25 |
Moline [15] | 30/12 | 73/50 | 83/60 | 86/64 | 84/62 | 76/53 | 64/42 | 48/30 | 34/18 | |||
Peoria [16] | 73/51 | 82/60 | 86/65 | 84/63 | 77/54 | 64/42 | 49/31 | 36/20 | ||||
Rockford [17] | 71/48 | 81/58 | 84/63 | 82/61 | 75/52 | 62/40 | 47/30 | 33/17 | ||||
Springfield [18] | 74/53 | 83/62 | 86/66 | 84/64 | 78/55 | 67/44 | 51/34 | 38/23 |
Average yearly precipitation for Illinois varies from just over 48 inches (1,200 mm) at the southern tip to just under 32 inches (810 mm) in the northern portion of the state. May and June are the wettest months of the year. Flooding is the most damaging weather hazard within the state. Increased warming within urban heat islands leads to an increase in rainfall downwind of cities. Lake Michigan leads to an increase in winter precipitation along its south shore due to lake effect snow forming over the relatively warm lakes. In summer, the relatively cooler lake leads to a more stable atmosphere near the lake shore, reducing rainfall potential. [5]
While normal annual snowfall exceeds 38 inches (0.97 m) in Chicago, the southern portion of the state normally receives less than 14 inches (0.36 m). [1] The snowiest winter on record for Chicago was 89.7 inches (2.28 m) during the winter of 1978–79. [19] The city has also recorded two other winters with snowfall in excess of 80 inches (2.03 m)—1977-78 and 2013-14. During the winter of 1830–31, southern sections of the state were covered with 3 feet (0.91 m) of snow, with drifts up to 6 feet (1.8 m) tall. Storms exceeding the normal winter value are possible within one day mainly in the southern half of the state. The heaviest snowfall recorded in Chicago history was 23 inches (0.58 m) during the Blizzard of 1967. [20]
Illinois averages around 50 days of thunderstorm activity a year which put it somewhat above average for the number of thunderstorm days for the United States. Thunderstorms contribute over half of the annual precipitation statewide. [5] Illinois is vulnerable to tornadoes with an average of 35 occurring annually, which puts much of the state at around 5 tornadoes per 10,000 square miles (30,000 km2) annually. [2] Peak tornado activity occurs between April and June. [5] Illinois also receives the remnants of tropical cyclones which have struck the Gulf coast. One of the wetter systems, Tropical Storm Claudette, impacted the state in July 1979 bringing rainfall amounts up to 7.64 inches (194 mm). [21]
The climate of Virginia, a state on the east coast of the United States, is mild compared to more northern areas of the United States such as New England and the Midwest. Most of Virginia east of the Blue Ridge mountains, the southern part of the Shenandoah Valley, and the Roanoke Valley, has a humid subtropical climate. In the mountainous areas west of the Blue Ridge, the climate is warm-summer humid continental or oceanic climate. Severe weather, in the form of tornadoes, tropical cyclones, and winter storms, impacts the state on a regular basis. Central Virginia received significant snowfall of 20 inches in December 2009.
The climate of Chicago is classified as hot-summer humid continental with hot humid summers and cold, occasionally snowy winters. All four seasons are distinctly represented: Winters are cold and often see snow with below 0 Celsius temperatures and windchills, while summers are warm and humid with temperatures being hotter inland, spring and fall bring bouts of both cool and warm weather and fairly sunny skies. Annual precipitation in Chicago is moderate and relatively evenly distributed, the driest months being January and February and the wettest July and August. Chicago's weather is influenced during all four seasons by the nearby presence of Lake Michigan.
The climate of Salt Lake City, Utah features cold and snowy winters, hot and dry summers, and modest to light seasonal rainfall. Lying in the Salt Lake Valley, the city is surrounded by mountains and the Great Salt Lake. Under the Köppen climate classification, Salt Lake City has either a Mediterranean climate (Csa) or dry-summer continental climate (Dsa) depending on which variant of the system is used, though it borders on a cold semi-arid climate (BSk) due to the city's relatively low precipitation.
The climate of Minneapolis–Saint Paul is the long term weather trends and historical events of the Minneapolis–Saint Paul metropolitan area in east central Minnesota. Minneapolis and St. Paul, together known as the Twin Cities, are the core of the 15th largest metropolitan area in the United States. With a population of 3.6 million people, the region contains approximately 60% of the population of Minnesota. Due to its location in the northern and central portion of the U.S., the Twin Cities has the coldest average temperature of any major metropolitan area in the nation. Winters are very cold, summer is warm and humid, snowfall is common in the winter and thunderstorms with heavy rainfall occur during the spring, summer and autumn. Though winter can be cold, the area receives more sunlight hours in mid-winter than many other warmer parts of the country, including all of the Great Lakes states, the Pacific Northwest, parts of the South, and almost all of the Northeast. Unless otherwise indicated, all normals data presented below are based on data at Minneapolis/St. Paul International Airport, the official Twin Cities climatology station, from the 1981−2010 normals period.
Milwaukee has a humid continental climate, with four distinct seasons and wide variations in temperature and precipitation in short periods of time. The city's climate is also strongly influenced by nearby Lake Michigan, which creates two varying climates within the Milwaukee area. The urban heat island effect also plays a role in the city's climate, insulating it from winter cold, but keeping it cooler in spring and summer.
Minnesota has a humid continental climate, with hot summers and cold winters. Minnesota's location in the Upper Midwest allows it to experience some of the widest variety of weather in the United States, with each of the four seasons having its own distinct characteristics. The area near Lake Superior in the Minnesota Arrowhead region experiences weather unique from the rest of the state. The moderating effect of Lake Superior keeps the surrounding area relatively cooler in the summer and warmer in the winter, giving that region a smaller yearly temperature variation. On the Köppen climate classification, much of the southern third of Minnesota—roughly from the Twin Cities region southward—falls in the hot summer zone (Dfa), and the northern two-thirds of Minnesota falls in the warm summer zone (Dfb).
The characteristics of United States rainfall climatology differ significantly across the United States and those under United States sovereignty. Summer and early fall bring brief, but frequent thundershowers and tropical cyclones which create a wet summer and drier winter in the eastern Gulf and lower East Coast. During the winter, and spring, Pacific storm systems bring Hawaii and the western United States most of their precipitation. Low pressure systems moving up the East Coast and through the Great Lakes, bring cold season precipitation to from the Midwest to New England, as well as Great Salt Lake. The snow to liquid ratio across the contiguous United States averages 13:1, meaning 13 inches (330 mm) of snow melts down to 1 inch (25 mm) of water.
The climate of Houston is classified as a humid subtropical climate, with tropical influences. August normally ranks as the warmest month at an average temperature of 95 °F (35 °C) and January the coldest month at an average temperature of 63 °F (17 °C).
The climate of the north and central parts of the U.S. state of Florida is humid subtropical. South Florida has a tropical climate. There is a defined rainy season from May through October when air-mass thundershowers that build in the heat of the day drop heavy but brief summer rainfall.
The climate of Alaska is determined by average temperatures and precipitation received statewide over many years. The extratropical storm track runs along the Aleutian Island chain, across the Alaska Peninsula, and along the coastal area of the Gulf of Alaska which exposes these parts of the state to a large majority of the storms crossing the North Pacific. The climate in Juneau and the southeast panhandle is a mid-latitude oceanic climate, in the southern sections and a subarctic oceanic climate in the northern parts. The climate in Southcentral Alaska is a subarctic climate due to its short, cool summers. The climate of the interior of Alaska is best described as extreme and is the best example of a true subarctic climate, as the highest and lowest recorded temperatures in Alaska have both occurred in the interior. The climate in the extreme north of Alaska is an Arctic climate with long, cold winters, and cool summers where snow is possible year-round.
Texas' weather varies widely, from arid in the west to humid in the east. The huge expanse of Texas encompasses several regions with distinctly different climates: Northern Plains, Trans-Pecos Region, Texas Hill Country, Piney Woods, and South Texas. Generally speaking, the eastern half of the state is humid subtropical, while the western half is largely semi-arid.
The climate of Georgia is a humid subtropical climate, with most of the state having short, mild winters and long, hot summers. The Atlantic Ocean on the east coast of Georgia and the hill country in the north impact the state's climate. Also, the Chattahoochee River divides Georgia into separate climatic regions with the mountain region to the northwest being cooler than the rest of the state; the average temperatures for the mountain region in January and July are 39 °F (4 °C) and 78 °F (26 °C) respectively. Winter in Georgia is characterized by mild temperatures and little snowfall around the state, with the potential for snow and ice increasing in the northern parts of the state. Summer daytime temperatures in Georgia often exceed 95 °F (35 °C). The state experiences widespread precipitation. Tornadoes and tropical cyclones are common.
The climate of the United States varies due to changes in latitude, and a range of geographic features, including mountains and deserts. Generally, on the mainland, the climate of the U.S. becomes warmer the farther south one travels, and drier the farther west, until one reaches the West Coast.
North Carolina's climate is varying, from the Atlantic coast in the east to the Appalachian Mountain range in the west. The mountains often act as a "shield", blocking low temperatures and storms from the Midwest from entering the Piedmont and Coastal Plain of North Carolina.
The climate of Pennsylvania is diverse due to the multitude of geographic features found within the state. Straddling two major climate zones, the southeastern corner of Pennsylvania has the warmest climate. A portion of Greater Philadelphia lies at the southernmost tip of the humid continental climate zone, with the city proper being in the humid subtropical climate zone. Still, Philadelphia features colder, snowier winters than most locations with a humid subtropical climate. Moving west toward the mountainous interior of the state, the climate becomes markedly colder, the number of cloudy days increases, and winter snowfall amounts are greater.
South Carolina has a humid subtropical climate, with hot summers throughout most of the state. But, an exception does occur in the Blue Ridge Mountains, as outlier pockets of an Oceanic Climate do exist. Mild winters predominate in the eastern and southern part of the state, but cool to occasionally cold winters are the standard in the northwestern area of the state, especially areas at or above 600 feet in elevation. On average, between 40 and 80 inches of precipitation falls annually across the state, potentially even in excess of 100 inches in portions of the Appalachian temperate rainforest. Tropical cyclones, and afternoon thunderstorms due to hot and humid conditions, contribute to precipitation during the summer and sometimes fall months, while extratropical cyclones contribute to precipitation during the fall, winter, and spring months. The coast experiences nearly all of their tropical weather impacts from storms coming directly from the Atlantic coast. The northwestern area of the state can receive impacts from both Atlantic basin storms moving westward from the coast and also occasionally very heavy rainfall and flooding from storms originating from the Gulf of Mexico that move inland towards the northeast after making landfall from the Florida Panhandle to Louisiana.
The climate of New York (state) is generally humid continental, while the extreme southeastern portion of the state lies in the warmer humid subtropical climate zone. Winter temperatures average below freezing during January and February in much of the state of New York, but several degrees above freezing along the Atlantic coastline, including New York City.
The Tampa Bay area has a humid subtropical climate, closely bordering a tropical climate near the waterfront areas. There are two basic seasons in the Tampa Bay area, a hot and wet season from May through October, and a mild and dry season from November through April.
The state of Alabama is classified as humid subtropical (Cfa) under the Köppen climate classification. The state's average annual temperature is 64 °F (18 °C). Temperatures tend to be warmer in the state's southern portion with its proximity to the Gulf of Mexico, while its northern portions, especially in the Appalachian Mountains in the northeast, tend to be slightly cooler. Alabama generally has hot, humid summers and mild winters with copious precipitation throughout the year. The state receives an average of 56 inches (1,400 mm) of rainfall each year and experiences a lengthy growing season of up to 300 days in its southern portion. Hailstorms occur occasionally during the spring and summer here, but they are seldom destructive. Heavy fogs are rare, and they are confined chiefly to the coast. Thunderstorms also occur year-around. They are most common in the summer, but they are most commonly severe during the spring and late autumn. That is when destructive winds and tornadoes occur frequently, especially in the northern and central parts of the state. Central and northern Alabama are squarely within Dixie Alley, the primary area in the U.S. outside the Southern Plains with relatively high tornado risk. Alabama is ranked second in the U.S for the deadliest tornadoes. Hurricanes are quite common in the state, especially in the southern part. Major hurricanes occasionally strike the coast, such as Hurricane Frederic in September 1979 and Hurricane Ivan in September 2004; both storms resulted in significant to devastating damage in the Mobile area.
The climate of New England varies greatly across its 500-mile (800 km) span from northern Maine to southern Connecticut.