Heat Alerts From Maine to the Mojave: Eastern Advisories End by Saturday Evening, Western Warnings Run as Late as Monday Morning

Forecast highs of 110 to 120 degrees across the Mojave Desert and air that will feel like 104 in New York City and Philadelphia belong to the same hot Friday. On Thursday, August 6, 2026, National Weather Service offices from Maine to the California desert posted Heat Advisories — and, in the Southwest, the more severe Extreme Heat Warnings — for Friday, August 7, and in many places beyond it. The eastern end times split in two: many zones’ advisories were written to end Friday evening, August 7, while those covering New York City, Long Island, northeastern New Jersey and the Philadelphia area were posted to run into Saturday, August 8 — though how long the New York-area advisory runs is disputed. The desert warnings go longer still — through Sunday, August 9, for most, and near Reno to Monday morning — and federal forecasters expect the western heat to spread over the weekend, not shrink.

One caution before the details: heat alerts expire, and they also get extended. Every Weather Service end time below is the one its issuing office posted on Thursday; before you plan around any of them, check the current alert for your own zone with the National Weather Service at weather.gov, where your ZIP code brings up the advisory or warning text for your own zone. A word about the numbers, too: in the humid East, the figures below are heat index values — the Weather Service’s measure of how hot the air will actually feel, humidity included — while in the dry Southwest they are plain air temperatures.

Key facts

What was posted: Heat Advisories from Maine to the California desert and, in the Southwest, Extreme Heat Warnings, issued Thursday, August 6, 2026, for Friday, August 7, and in many places beyond it.
Hottest forecast: 110 to 120 degrees across the Mojave Desert, in a warning that also covers Death Valley and the Las Vegas Valley, with overnight lows of 80 to 95.
Highest heat index values: up to 109 in Lee and Phillips counties in Arkansas and Coahoma and Tunica counties in Mississippi, up to 108 across Oklahoma and neighboring north Texas, and up to 104 in New York City and the Philadelphia area.
Last alert to end: western Nevada, where the Reno office’s Extreme Heat Warning runs through 8 a.m. PDT Monday, August 10.
Reading the numbers: in the humid East they are heat index values; in the dry Southwest they are plain air temperatures.
Not all from the Weather Service: Los Angeles County’s public health department issued its own Extreme Heat Warning for the Antelope Valley and its own Heat Advisory for the county’s mountain corridors, both through Saturday, August 8.
Where to check your own zone: the National Weather Service at weather.gov, by ZIP code — alerts expire, and they also get extended.

When the alerts end

Thursday, August 6: National Weather Service offices from Maine to the California desert post the Weather Service alerts in this article; Los Angeles County’s two alerts are already running.
Friday, August 7: most Northeast advisories end Friday evening, as do the higher-elevation northern New Jersey and Pennsylvania zone, the Oklahoma, north Texas and Arkansas advisories and the Memphis office’s advisory; the Grand Canyon warning ends 8 p.m. MST and the Medford advisories 11 p.m. PDT; the Puget Sound advisory was posted to end 10 p.m. PDT. Western Nevada’s Heat Advisory becomes an Extreme Heat Warning at 8 a.m. PDT.
Saturday, August 8: the New York City, Long Island and northeastern New Jersey advisories were posted to run into this day, though that end time is disputed; the Philadelphia, northern Delaware and central and southern New Jersey advisory runs through Saturday evening; Los Angeles County’s two alerts run through Saturday.
Sunday, August 9: the Phoenix warning runs through Sunday, the Las Vegas and San Joaquin Valley warnings until 8 p.m. PDT, and the Sacramento office’s advisory until 10 p.m. PDT.
Monday, August 10: the Reno office’s Extreme Heat Warning for western Nevada runs through 8 a.m. PDT.

The Northeast

Every time in this section is Eastern. Each alert below carries the office that posted it, the heat index it forecast, and the end time that office posted.

New York City, northeastern New Jersey and Long Island: posted by NWS New York, heat index up to 104 in the city and up to 100 on Long Island, running into Saturday, August 8. The available reporting disagrees on how long it runs, so the time to trust is the one on the New York office’s own alert page.
The Lower Hudson Valley: also from NWS New York, heat index up to 98, ending 8 p.m. EDT Friday, August 7.
Coastal Connecticut: also from NWS New York, heat index up to 99, running through Friday evening, August 7.
Eastern and central Massachusetts, Rhode Island and northern Connecticut: NWS Boston, heat index up to 100, running through Friday evening, August 7.
South-central Maine and central New Hampshire: NWS Gray, Maine, heat index up to 99, ending 8 p.m. EDT Friday, August 7.
Parts of eastern Maine: NWS Caribou, heat index up to 97, ending 6 p.m. EDT Friday, August 7.

Philadelphia and New Jersey

The Mount Holly office posted two advisories for this area, and they end on different days.

Philadelphia, northern Delaware, and central and southern New Jersey: heat index up to 104, posted to run through Saturday evening, August 8.
The higher-elevation northern zone: heat index up to 102, running through Friday evening, August 7. That zone covers Sussex, Warren, Morris and Hunterdon counties in New Jersey, and Berks, Lehigh and Northampton counties in Pennsylvania, along with western Chester, western Montgomery and upper Bucks counties.

The Plains and the Mid-South

The Norman and Tulsa offices posted Heat Advisories on Thursday evening across much of Oklahoma, neighboring north Texas counties and west-central Arkansas, with heat index values up to 108. As posted, both alerts run through Friday evening, August 7. The Memphis office’s advisory for Lee and Phillips counties in Arkansas and Coahoma and Tunica counties in Mississippi carries the highest heat index in this group, up to 109, also through Friday evening.

The West

The top-tier warnings are in the deserts, and the longest of them outlast everything east of them. One note on clocks: the two Arizona alerts below are posted in Mountain Standard Time, Arizona’s own zone, and every other time in this section is Pacific.

Arizona

Phoenix: NWS Phoenix’s Extreme Heat Warning covers the metro area, with afternoon temperatures of 108 to 114, through Sunday, August 9.
Grand Canyon: the Flagstaff office’s Extreme Heat Warning covers the canyon corridor below 4,000 feet, at 100 to 113 degrees — 110 to 113 at Phantom Ranch — until 8 p.m. MST Friday, August 7.

California and Nevada

Las Vegas: an Extreme Heat Warning covers the Las Vegas Valley, Death Valley and the Mojave Desert, with highs of 110 to 120 forecast across the Mojave Desert and overnight lows of 80 to 95, through 8 p.m. PDT Sunday, August 9.
San Joaquin Valley: the Hanford office’s Extreme Heat Warning calls for daily highs of 105 to 108, up to 112 in spots, with overnight lows of 75 to 80 offering little relief, until 8 p.m. PDT Sunday, August 9.
Central California: the Sacramento office’s Heat Advisory for the Sacramento and San Joaquin valleys, with highs of 102 to 108, runs from 10 a.m. Friday until 10 p.m. PDT Sunday, August 9. Yes, the San Joaquin Valley appears twice: the Hanford warning and the Sacramento advisory are separate alerts at different severity levels, and the one posted for your own zone is the one that applies to you.
Western Nevada: the Reno office’s alert for the Basin and Range country, including Pyramid Lake, starts as a Heat Advisory and becomes an Extreme Heat Warning at 8 a.m. PDT Friday. The warning then runs through 8 a.m. PDT Monday, August 10 — the latest end time of any alert in this article.

The two alerts from Los Angeles County

Two of the alerts in this section did not come from the Weather Service at all. Los Angeles County’s public health department issues on its own authority, and it has extended its own Extreme Heat Warning for the Antelope Valley and its own Heat Advisory for the county’s mountain corridors, both through Saturday, August 8. Changes to those two will come from the county, so its releases are the ones to watch.

Oregon and Washington

Farther north, the Medford, Oregon office posted advisories with highs of 100 to 105 in the Rogue Valley, and possibly 110 in the Klamath River Valley, until 11 p.m. PDT Friday. The Seattle office’s Puget Sound advisory, with highs of 85 to 90, was posted to run until 10 p.m. PDT Friday.

Excessive Heat Warning or Extreme Heat Warning?

For years the Weather Service’s top heat product was widely known as an Excessive Heat Warning, and plenty of explainers still use that name. But the agency’s most severe heat alerts active Thursday carried the label Extreme Heat Warning — its own live national alert feed, queried Thursday, listed none under the old name and a dozen or more under the new — and its safety pages define the levels the same way: “An Extreme Heat Warning is issued when extremely dangerous heat conditions are expected or occurring,” while “A Heat Advisory is issued for dangerous heat conditions that are not expected to reach warning criteria.” An Extreme Heat Watch sits between them, for extreme-heat events whose occurrence and timing are still uncertain.

There is no single temperature that triggers any of them. The Weather Service says local offices set their own criteria with local partners, because “residents of Florida are much more prepared for 90F+ weather than residents in Alaska.”

The weekend forecast

NOAA (National Oceanic and Atmospheric Administration)’s Weather Prediction Center, in a forecast discussion issued Thursday afternoon, said “Dangerous heat expands across the Southwest, Intermountain West, Rockies, and the central/southern Plains into the weekend,” with highs surging “well into the 90s and 100s” and “Numerous daily temperature records are likely beginning on Friday and continuing each day through Sunday.” That expansion language covers the West and the Plains; the Northeast advisories carry the posted end times above.

What to do, and the signs that mean 911

CDC (Centers for Disease Control and Prevention) guidance for days like this is short: stay in air-conditioned spaces, drink fluids even when you are not thirsty, wear loose, light-colored clothing, and keep strenuous activity out of the hottest hours. The people at highest risk are young children, older adults, pregnant people, outdoor workers, and people with heart conditions or on low-sodium diets — worth remembering when deciding whom to check on. Los Angeles County’s health department asks residents to look in on elderly, chronically ill and isolated neighbors twice a day, and urges the use of cooling centers.

If you do not have air conditioning

Los Angeles County’s health department urges its residents to use cooling centers, and that instruction speaks for that county alone. Where to find a cooling place near you is a question for your own city or county, not a national page.

Signs of heat stroke

Heat stroke is the emergency. The CDC’s danger signs include a body temperature of 103 degrees or higher, headache, nausea, dizziness and confusion; Los Angeles County tells residents to call 911 for a high fever, confusion or fainting.

Never leave anyone in a parked car

And the bluntest line on the Weather Service’s heat safety page is a year-round rule that matters most on days like these: “It is NEVER safe to leave a child, disabled person or pet locked in a car, even in the winter.”

If your town is not named

Absence from this article is not absence from the map: Thursday’s feed also carried heat advisories in parts of Idaho, Colorado, Utah and New Mexico, among other areas not detailed here, so check your own ZIP even if your town was not named. For a broader view, NOAA’s HeatRisk map grades forecast heat on a five-color scale from green to magenta, aimed at heat-sensitive people and planners; the agency labels the tool experimental, so treat it as a supplement to the official alerts, not a replacement.