Heatwave and high humidity to blast much of US: ‘impactful to anyone’

A long and dangerous Heatwave will blast a large swath of the central and eastern United States for the upcoming week, the National Weather Service (NWS) said on Sunday – with temperatures rising ahead of the Fourth of July holiday and feeling even hotter because of high humidity also arriving.Already parts of the US, especially Phoenix and central Texas, and much of the south-west were experiencing temperatures of about 100F (38C) on Sunday, while the NWS warned of severe wildfire conditions developing across much of the west as new fires popped up across the region.On Sunday, more than 130 million Americans across southern and Great Plains states were under moderate to severe heat risk conditions, according to NWS maps, with that area forecast to expand and temperatures to intensify as the week drags on.Forecasters say several days of high temperatures – some above 100F – will settle in across the lower Great Lakes, the mid-Atlantic and the Mississippi and Ohio River valleys. Some record highs could be set in areas from the lower Great Lakes to the mid-Atlantic and New England later in the week, NWS meteorologist Bryan Putnam said.A number of big cities could see their highest temperatures of the year so far as they host World Cup matches and celebrations for the US’s 250th anniversary.Feeling the heat will be the east coast cities of New York City, Philadelphia, Washington and Baltimore, and midwestern and Great Lakes cities including Chicago, Indianapolis, St Louis and Detroit. Southern cities such as Dallas; Little Rock, Arkansas; and Memphis, Tennessee, will also see high temperatures.High heat will last into next weekend across the Great Plains, the south-east and the mid-Atlantic, the NWS said.Temperatures will reach well into the 90s and low 100sF, the NWS said. High humidity will lead to heat indexes of 100-110F, and as high as 115F.“That’s heat that’s impactful to anyone,” Putnam said. “It’s not just older adults or younger children or people who are spending a ton of time outdoors, maybe straining themselves a little more than normal. This is heat that really could impact everyone, especially with people outdoors going into the holiday weekend.”The heat index, which factors in humidity and is included on many weather forecasts, provides a sense of how hot it really feels – and what’s dangerous for prolonged exposure or strenuous activity.People are seen at the Hole-in-the-Rock as temperature hits 107F at the Papago Park in Phoenix, Arizona, on 8 June. Photograph: Anadolu/Getty ImagesTyler Roys, an AccuWeather meteorologist, said temperatures will be significantly above normal. For instance, in Washington DC, highs around the Fourth of July holiday average about 89F, while Indianapolis averages about 85F. For the stretch in question, both cities can expect to be hotter by 10 or 11F, Roys said.The high pressure system – an area of dry, sinking air – creating the heat will act like a “rock” that will force storms to go around it and limit rainfall across the east, Roys said. That’s sometimes called a “heat dome”.Nightly lows in the 70sF or even high 80s won’t provide much relief, meteorologists said.For those who don’t have air conditioning, especially in eastern seaboard cities such as New York where lows may not dip below 80F, it’s going be miserable to sleep, Roys said.Roys also said this is a prime time for heat-related illnesses because people’s bodies aren’t able to recover and cool off.During extreme temperatures, limit outdoor activity, stay hydrated and ensure access to air-conditioning and other cooling areas, the weather service said.The weather service said it expected extremely dry and windy conditions that could promote rapid wildfire spread across the Great Basin and the south-west on Sunday.In hot, windy conditions near the Colorado-Utah border, three firefighters working for the US Wildland Fire Service and US Forest Service were reported killed – and two others sustained burn injuries, when they were overcome by flames from fast-moving wildfires.Wildfire activity has intensified across the western US as hot, dry and windy weather fueled flames in Utah, Colorado, Arizona and elsewhere.Instances of extreme weather – including dangerous heat and conditions that are ripe for wildfires – are symptomatic of the world’s ongoing climate crisis, which is primarily driven by carbon emissions from the burning of fossil fuels.Guardian staff contributed reporting