The eastern US is covered with air quality alerts from Iowa to Maine, including New York, as smoke from Canadian wildfires billows south for another day.In New York City, the air quality index ranges from 50 to 70 in many places, implying that people who suffer from respiratory ailments should stay indoors, according to AirNow.gov. New York and Chicago can expect bad air through midnight, according to alerts posted by the National Weather Service.

Further to the south and west conditions are worse. Air in Chicago, Pittsburgh, Madison, Wisconsin, and Davenport, Iowa is “very unhealthy” while conditions in Washington and Cincinnati are “unhealthy,” AirNow.gov shows. In Canada, conditions are “moderate” in Montreal and “unhealthy for sensitive groups” in its capital Ottawa.On Wednesday, 1,198 flights around the US were cancelled, with most of them traveling to or from Newark, New York, and Chicago, according to Flight Aware. Canada enters a long holiday weekend with 500 fires burning across the country, according to the Canadian Interagency Forest Fire Centre. So far this year, 3,030 fires have consumed 8 million hectares of land, or about 30,888 square miles of charred area.

Meanwhile, heat continues to sear down across the lower Mississippi River Valley and parts of the southern Great Plains, including eastern Texas. Extreme temperatures are also building in southern Oregon through California into Arizona.

The high in Dallas is forecast to reach 104F (40C) on Thursday with a heat index of 109 when humidity is factored in, the National Weather Service said. In Del Rio, Texas, the string of daily record high temperatures was extended to an eleventh day Wednesday when readings reached 108F, tying the previous high for the date set in 1994. The streak may end Thursday.

The worst of the heat will be focused along the Mississippi River from Cairo, Illinois in the north, where it joins the Ohio River, to New Orleans, where it empties into the Gulf of Mexico, In California, highs in Sacramento could reach 101F Thursday and push to 107F by Saturday, the National Weather Service said.

All the heat is going to melt a lot of snow that is still in the mountains, so flood warnings and watches are up in the Sierra Nevada. As this coincides with the Fourth of July holiday, it means people swimming in the mountain streams risk freezing in cold snowmelt water or being swept downstream. People are warned not to leave pets and children wandering around the edges of mountain waters.In other weather news:El Nino: New Zealand could face an El Nino weather pattern in late winter or early spring, the National Institute of Water and Atmospheric Research says in its Seasonal Climate Outlook Thursday in Wellington.UK: The nation needs more planning around securing the water supplies due to rising demand and record hot weather.

Europe: Water levels at a chokepoint on the Rhine have fallen to a seasonal low.