The National Weather Service has 33 heat advisories active Sunday across 16 states, stretching from Montana’s high plains to inland Southern California and the Maine coast, as forecasters track dangerously high heat index values persisting into the middle of the week.
Advisories are posted in California, Colorado, Idaho, Massachusetts, Maine, Michigan, Minnesota, Montana, Nevada, New York, Pennsylvania, Puerto Rico, South Dakota, Vermont, Wisconsin and Wyoming. The alerts cluster in three regions: the northern Rockies and high plains, the Colorado Front Range and inland Southern California, and the Northeast.
In Montana, the Weather Service has posted highs in the mid-90s for Central and Southeast Phillips, Central and Southern Valley, Garfield, McCone and Petroleum counties, in effect until 2 a.m. MDT Tuesday. A separate advisory covers Daniels, Northern Phillips, Northern Valley, Sheridan, Southwest Phillips and Western Roosevelt counties, with highs of 90 to 95 degrees over the same window.
Farther south, the agency has flagged heat index values of 95 to 105 across portions of northwestern, south-central and southwestern South Dakota and northeastern Wyoming. That advisory runs until 9 p.m. MDT — 10 p.m. CDT — Thursday, one of the longer-duration alerts in the current batch, covering areas including Rapid City, Sturgis/Piedmont Foothills, the Pennington and Custer county plains, and Ziebach, Haakon, Bennett, Mellette, Todd and Tripp counties.
In Colorado, the advisory zone runs along the Front Range below 6,000 feet, including Larimer and northwest Weld counties, Boulder, Jefferson and Broomfield counties, and the Denver metro corridor through north Douglas, west Adams and Arapahoe counties. Inland Southern California is also under advisory, with the National Weather Service naming the Santa Clarita Valley, the western and eastern San Fernando Valley, the San Gabriel Valley and interior valleys and mountains of San Luis Obispo, Santa Barbara and Ventura counties — heat building away from the moderating coastline, including the Los Angeles County inland coast around downtown Los Angeles.
In the Northeast, advisories cover inland Maine counties including Oxford, Franklin, Somerset, Cumberland, Kennebec and Androscoggin, part of a broader push that also includes Massachusetts and Vermont.
The National Weather Service is urging residents in advisory zones to never leave children or pets unattended in vehicles, warning that car interiors can reach lethal temperatures within minutes. The agency also recommends drinking plenty of fluids, staying in air-conditioned spaces and limiting outdoor activity during peak afternoon heat.
With 33 advisories active at once, the story is less about a single record than about reach: heat stress spanning roughly a third of the country’s states simultaneously, from the Pacific Coast to Puerto Rico and the high plains to New England.