Brutal Heat-wave Across Central and Eastern US

A punishing heat-wave has settled over central and eastern parts of the US, pushing temperatures as high as 37C (99F) and causing up to 22 deaths.
The National Weather Service warned of "dangerous" levels of heat and humidity creeping east, with no relief expected in eastern states until Sunday. As much as 50% of the US population is under a heat advisory, officials said.

Meteorologists have put the temperatures down to a "dome" of high pressure in the atmosphere. On Thursday, many regions in the central US and parts of the eastern seaboard also saw heat indexes - a combination of temperature and humidity - topping 43C or approx.109F. The air is sinking, as it sinks it compresses and gets warmer. It also dries out, so few clouds form to block the high early-summer sun.
Meanwhile, asphalt and concrete pavements and buildings in cities were "re-radiating" the heat.

Heat is the number one weather-related killer in the US, according to the National Weather Service.
Across the central and eastern US, people and animals alike have been struggling to keep cool amid the oppressive heat and humidity. As the heat peaks in major population centres on the east coast, the number of deaths is expected to rise, officials warn. The combination of high heat and high humidity made it hard for the human body to cool itself - because sweat does not evaporate efficiently.

 In Minnesota - a northern state known for its frigid winters - farm livestock have been dying from heat stress at a rate not seen in three decades, the Minneapolis Star Tribune newspaper reported. Turkeys were hit especially hard, the paper reported. In South Dakota, as many as 1,500 head of cattle have died in the heat, state veterinarian Dustin Oedekoven told Reuters news agency.

Urban areas have opened cooling centres for the poor and elderly, and the National Weather Service has warned people in normally cool areas to be especially cautious. Philadelphia has deployed police officers to manage hot, irritated crowds at the city's public swimming pools.   Con Edison said scattered power cuts were likely in New York in the next several days amid a surge in usage of air conditioning units.

Chicago is experiencing unhealthy smog levels caused by the heat. The Illinois Environmental Protection Agency asked the city's residents to reduce polluting activities, such as mowing lawns and keeping the engines running on stationary vehicles. Forecasters said the damage caused by the heat could be worse than that brought about by a heat-wave in Chicago in 1995, when more than 700 people died over three days.

 By Friday, the low pressure system moving east is expected to bring thunderstorms with hail to the north-eastern US. Meanwhile, as half of the country's 310 million residents sizzle, states in the north-western region of the country were experiencing abnormally cool temperatures. "I didn't know it could be this cold in July. It is absolutely freezing here in Seattle," said one user of Twitter.

The most severe heat-wave in modern North American history took place during the Great Depression in 1936. The heat that summer was blamed for more than 5,000 deaths in the US and Canada.