More than 70 million people were under heat alerts, including St Louis, Kansas City, Oklahoma City, Memphis, Nashville, New Orleans and Atlanta, where heat index values of 105° to 110° degrees are expected.
“Furthermore, Heat Advisories are currently in effect for portions of the Pacific Northwest/Northern California and over Middle/Lower Mississippi/Tennessee Valleys and adjacent Plains.”
Dangerous heat spread Thursday from southern Nebraska to Georgia, where humid Gulf moisture raised heat index values.
“Hot and humid conditions will continue through the remainder of the week with afternoon temperatures in the middle 90s to around 100°F and heat indices up to 110°F to 115°F over consecutive days,” said the National Weather Service office in Jackson, Mississippi. “This is a prolonged heat wave.”
These high temperatures, with conditions feeling even hotter due to humidity, will be the same story for much of the central and southern US.
Dallas; Tulsa, Oklahoma; New Orleans and Atlanta could all see searing conditions throughout the weekend as the heat dome spreads over the South.
By Saturday, near triple digit heat will spread from Texas to South Carolina, with sweltering heat index values topping 105°.
A cold front drops through by Sunday night into the start of the week, bringing cooler, seasonal temperatures back to the region.
Heat returns to the Pacific Northwest
An unwelcome return of above-normal temperatures will impact Oregon, northern California, and parts of Washington and Idaho the next several days.
Heat advisories are in effect across the inland Northwest, as well as excessive heat warnings in southwestern Oregon, where temperatures could climb to 110 degrees.
Temperatures on Friday could near 100 degrees in Portland, well above the seasonal 70s in July.
“One of the things that we’re a bit concerned about is the potential for lightning in the areas that are very dry this season because of the drought. The vegetation is very dry and receptive to starting a fire if lightning strikes,” said Weagle.
Isolated dry thunderstorms are possible in the area through Friday, bringing the threat for more lightning strikes to ignite wildfires in the drought-ridden area amid the elevated heat.
Pyrocumulus clouds have been prevalent in the fires burning across the Pacific Northwest this summer due to extreme fire behavior amid very dry and hot conditions.
These massive plumes of smoke happen when extremely hot wildfires create their own weather, which can include lightning, thunder and even tornadic rotations. They loft huge amounts of smoke high into the atmosphere, where it can be carried across the country.
Air quality alerts are in effect in Montana, Idaho, Wyoming and Colorado due to Western wildfire smoke creating polluted air.
Hot temperatures through the end of the week and dry conditions will pose a risk for more extreme wildfire behavior and the potential for new fires to start.
Seasonal temperatures return by late weekend, when monsoon moisture moves into the region.
Heat can be deadly
The danger of heat stroke is “imminent” with prolonged outdoor activity in these hot and muggy conditions according to NWS Jackson.
The heat index is an indicator of what the temperature feels like to the human body when the humidity and air temperature are both taken into account.
When it is hot out, our bodies create sweat that is evaporated, cooling us down. But when it is very humid, it is difficult for the moisture to evaporate, making it feel hotter and increasing the risk of heat stroke.