Present Climate of the Midwest

Nearly all of the Midwest has a humid continental climate, describing temperatures that vary greatly from summer to winter, and appreciable precipitation year-round. This is represented in the Köppen system with the prefix “D.” Southernmost Illinois and Indiana are closer to a humid subtropical climate, or “C,” the primary difference being warmer winters than are found in a D climate. While averages are important factors in describing climate, the Midwest has unusually extreme annual variation in temperature. At an average temperature of 10°C (50°F), it seems similar to that of England, which has an average of 8°C (47°F). But England’s average high temperature of 21°C (70°F) and low of 2°C (35°F) is more indicative of how different their climate truly is. Average highs in the Midwestern states are around 29°C (85°F), with lows around -9°C (15°F), a variation fully twice as great as England’s. Furthermore, each state has record high temperatures of more than 43°C (110°F) and lows of less than -34°C (-30°F)—a variation of a whopping 77°C (140°F)!

The Midwest is one of the most productive agricultural areas in the world, and the economies of its states depend on farmland. Its excellent soil, relatively flat geography, and bodies of water make it uniquely suited to cropland. Yet without a humid climate with warm summers, agriculture here would be completely different. It is one of the few places on Earth where huge amounts of corn and soybeans can be grown with little or no irrigation.

Weather

In part because of its climate’s extreme temperature variation and humidity, the Midwest experiences nearly every variety of severe weather. Because the states are so far from the coasts, they rarely experience hurricanes, but heat and cold waves, droughts, floods, blizzards, and tornados are all fairly regular events.

Thunderstorms

The Köppen Climate Map

Wladimir Köppen developed a commonly used system of climate categorization based on the kinds of vegetation areas sustain. He defined 12 climate types, many of which are familiar: rainforest, monsoon, tropical savanna, humid subtropical, humid continental, oceanic, Mediterranean, steppe, subarctic, tundra, polar ice cap, and desert. Updated by Rudolf Geiger, it has been refined to five groups each with two to four subgroups.

The geography and climate of the Midwest are nearly ideal for the formation of thunderstorms. Storms occur when there is strong convection in the atmosphere. Because warm air can hold more moisture than cool air can, convective mixing with cool air forces moisture to condense out of warm air, as vapor (clouds) and precipitation. It is hypothesized that the formation of precipitation causes the electrical charging that produces lightning. Of course, air cannot mix without moving, and that movement is caused by the wind.

A strong temperature difference at different heights creates instability—the warmer the air near the surface is relative to the air above it, the more potential energy it has to move up. The Midwest frequently gets warm, moist air moving north from the Gulf of Mexico, and cold, dry air moving in from the Rocky Mountains or Canada. Where they meet, vigorous mixing causes storms. Typically, a storm blows itself out once the warm air has moved up and the cool air down—a vertical column turning over as a unit. But because the lower air from the Gulf is moving north while air higher up is moving west, more heat and moisture is constantly added to the system, allowing the storm to persist and strengthen. This movement in different directions is also the reason for the area’s unusually high incidence of powerful tornados.

Tornados

Tornado Alley is a nickname for an area extending from Texas to Minnesota (including the western Midwest) that experiences a high number of exceptionally strong tornados. Correcting for size, Indiana and Iowa are the states with the third and fourth most tornados respectively. A few other places in the world see tornados more frequently per given area, but those in central North America tend to be much more powerful. The thunderstorms discussed above can sometimes produce dozens of violent tornados, called tornado outbreaks.

Midwestern Tornado Map

Number of average tornadoes per year in the Midwestern states.

Lake Effect

The Great Lakes create an interesting phenomenon primarily on their eastern shores, mainly affecting Michigan as well as parts of the Northeast, known as the lake effect. During the winter, the huge volume of water in the Great Lakes acts as a reservoir of heat, making the air above it relatively warm and humid. When cold air moves across the warmer lake, convection begins, and, as described above, a storm can form. The moisture from the lake begins to precipitate soon after the air cools. The Upper Peninsula of Michigan usually receives over five meters (200 inches) of snow per year, second only to Tug Hill Plateau in New York, which also gets lake effect snow.

All of the states of the Midwest experience winter storms to some extent, during which several inches of snow falls. While inconvenient and damaging to infrastructure, these storms do not frequently cause widespread disruption, as residents and governments are usually prepared to clear roads and repair damage. Additionally, schools have snow days calculated into their schedules. Ice storms can be more dangerous;; as rain freezes to trees, power lines, and rooftops, they may collapse under the weight. If you are able to un-encase your car, the icy roads are even more dangerous to drive on than snowy ones.