Major to extreme heat risk expands across the central U.S.
More than 55 million Americans are under heat advisories Friday, with additional alerts likely to be posted this weekend. Some parts of the Midwest may experience their hottest temperatures so far this year.
Cities under alert to close the workweek include Omaha, Wichita, Oklahoma City, Dallas, Little Rock, then extending southeast to New Orleans, Birmingham, Alabama, Tallahassee and Orlando.
Many of these spots will see heat indexes in a 105-110 or higher range, with actual temperatures in the upper 90s to around 100. Those types of readings will shift east somewhat in the days to come.
The cause is a familiar one: A heat dome of high pressure covers much of the Lower 48 on Friday. It’s in no hurry to move ahead, although by next week it may return to the Desert Southwest.
Until then, heat continues to blast portions of the central and eastern U.S. through the middle of next week, before ultimately getting squashed into the South as a cold front presses that direction and tries to help steer Tropical Storm Erin away from the East Coast.
In some spots, it’ll be summer’s worst
As temperatures step upward through the start of next week, several days of major to extreme heat risk will be focused on the Midwest, with tendrils extending south along the Mississippi River Valley.
In parts of the Ozarks through the lower Midwest in particular, highs approaching 100 degrees on Saturday through Tuesday should threaten or topple prior numbers for maximums this year. Prior highs are mainly in the mid- or upper 90s during a late-July heat wave.
St. Louis, where summer is averaging about a degree above the 1991 to 2020 normal, has topped out at 97 degrees to date. The Weather Service forecasts St. Louis to reach 99 or 100 degrees every day from Saturday through Monday.
It’s a similar tale in Paducah, Kentucky, where the maximum temperature this summer is 95 degrees. There, the forecast calls for highs above the century mark every day from Friday through Tuesday. The highest temperatures are anticipated both Sunday and Monday, when it is expected to reach 100.
A number of long-term climate locations in the region are eyeing record highs, particularly Monday and Tuesday. This risk seems centered on locations like Paducah, Louisville and Memphis, although it may expand somewhat as forecasts are refined.
High humidity makes it feel worse
Seasonably high humidity will only make managing more difficult.
The combination of dew points - a measure of humidity - ranging from around 70 to 75-plus degrees in much of the hardest hit region means heat index values will regularly top 105 degrees through the weekend and into early next week.
Heat indexes will approach 110 in Dallas, Tulsa, New Orleans and Mobile, Alabama, among other spots. The Weather Service outlook calls for heat index values as high as 117 in part of Mississippi through Tuesday.
Given the extended length of temperatures as hot or hotter than they have been all summer, plus limited cooling at night, heat illness will be a significant concern across a wide swath of the south-central U.S. In many cities that rise near 100 during the day, overnight temperatures will only fall to the mid- or upper 70s.
The Climate Shift Index by Climate Central indicates that a majority of the region impacted by this round of heat is in an area of temperatures 3-5 times more likely due to climate change.
Will there be relief ahead?
A frontal zone locked up near the international border, on the north end of the ongoing heat dome, will eventually make a move south early next week. At first it will get stick around the Great Lakes, but thereafter it should head toward the Deep South.
This change in the pattern eventually means a shot at sustained cooler than normal conditions for those recently dealing with heat, especially in the Great Lakes and Northeast as the heat dome shifts toward the Desert Southwest and Tropical Storm Erin hopefully gets deflected back out to sea.