Reuters, Chicago : A blast of Arctic air gripped the vast middle of the United States on Monday, bringing the coldest temperatures felt in two decades, causing at least four deaths, forcing businesses and schools to close and canceling thousands of flights. Shelters for the homeless were overflowing and the weather threatened to briefly curtail some oil production in the severe cold described by some meteorologists as the ” polar vortex” and dubbed by media as the “polar pig”. Temperatures were 20 to 40 degrees F (11-22 degrees C) below average in parts of Montana, North and South Dakota, Minnesota, Iowa, Wisconsin, Michigan and Nebraska, according to the National Weather Service. More than half the flights at Chicago’s O’Hare International Airport were closed as fuel supplies froze, leaving crews unable to fill aircraft tanks. The afternoon temperature in Chicago was minus 12 degrees Fahrenheit (minus 24 degrees C), making it colder than in areas of Antarctica, parts of which hovered around 32 F (0 C) during the southern hemisphere summer. The Arctic air was moving toward the east coast where temperatures were expected to fall throughout Monday as low as 0 degrees Fahrenheit (minus 18 degrees celsius) in some areas on Tuesday. The coldest temperatures in years and gusty winds were expected as far south as Brownsville, Texas and central Florida, the National Weather Service said. The northeast saw unseasonably mild weather and rain, but authorities warned travelers to expect icy roads and sidewalks on Tuesday. At least four weather-related deaths were reported. In northwest Missouri, a one-year-old boy died Monday when the vehicle he was riding in crashed into a snow plow on an icy highway, according to the Missouri State Highway Patrol. In Indianapolis, firefighters found the body of an elderly woman outside her home early on Monday. “It appeared she had been there for a while,” said Captain Michael Pruitt of the Wayne Township fire department. A 58-year-old man died on Sunday in northeastern Oklahoma after he lost control of his car on icy roads, the Oklahoma Highway Patrol said. In Chicago, a 48-year-old man died of a heart attack while shoveling snow on Sunday night. In oil fields from Texas to North Dakota and Canada, the severe cold threatened to disrupt traffic, strand wells and interrupt drilling and fracking operations. It also disrupted grain and livestock shipments throughout the farm belt, curbed meat production at several packing plants and threatened to damage the dormant wheat crop. In Cleveland, Ohio, where the temperature was minus 3 degrees F (minus 19 degrees C) and was forecast to drop to minus 6 degrees F (minus 21 degrees C) overnight, homeless shelters were operating at full capacity. Shelter operators had begun to open overflow facilities to accommodate more than 2,000 people who had come seeking warmth.