Excessive Heat Warning
vs. Heat Advisory
Both mean the heat is dangerous, not just uncomfortable. The difference is how dangerous, and how the National Weather Service wants you to respond.
It's Based on Heat Index, Not Temperature
Both products are triggered by the heat index — what the temperature actually feels like once humidity is factored in — not the raw thermometer reading. A 95°F day with high humidity can feel over 110°F, and that's the number that matters for these alerts.
Exact thresholds vary by region, since 100°F feels routine in Phoenix but dangerous in Minneapolis. Local NWS offices set criteria based on what's actually unusual and risky for their area.
The Two Alert Levels
Heat Advisory
Heat index is expected to reach a level that's uncomfortable and can cause heat-related illness with prolonged exposure or physical activity — roughly heat index 100–104°F in many regions, lower in cooler climates. Take precautions, but daily activities generally continue.
Excessive Heat Warning
Heat index is expected to reach a level that poses a significant, even life-threatening, risk — typically 105–110°F+ sustained for two or more hours, though thresholds vary by region. This is the "change your plans" tier.
An Excessive Heat Watch can also be issued a day or two ahead, when dangerous heat is possible but not yet certain — same relationship as any other watch.
Heat Exhaustion vs. Heat Stroke
Heat Exhaustion
Heavy sweating, cold or clammy skin, weak pulse, nausea, headache, dizziness, muscle cramps. Move to a cool place, sip water, apply cool cloths. Seek medical help if symptoms worsen or last over an hour.
Heat Stroke — Emergency
Body temperature above 103°F, hot/red/dry skin (sweating may have stopped), fast strong pulse, confusion, loss of consciousness. Call 911 immediately. Move to a cool area and cool the body with whatever's available while waiting.
Who's Most at Risk
Older adults, infants and young children, people with chronic illness, outdoor workers, athletes, and anyone without reliable air conditioning face the highest risk. Never leave a person, child, or pet in a parked vehicle — interior temperatures can climb over 20°F above the outside air within 10 minutes.
Heat Is the Deadliest Weather Hazard
Extreme heat kills more people in the US each year, on average, than any other weather hazard — more than tornadoes, hurricanes, and floods combined, according to NWS long-term data. It doesn't get the same attention because it doesn't destroy property or make dramatic footage; the damage is medical, quiet, and disproportionately affects people who are isolated, elderly, or without reliable cooling. Checking on neighbors during a multi-day Excessive Heat Warning is not just a courtesy — it's one of the more effective things an individual can do to reduce the death toll of a heat wave.
Staying Safe Without Reliable AC
Find a Cooling Center
Many cities and counties open public cooling centers during Excessive Heat Warnings — libraries, community centers, and malls also work as free air-conditioned refuges during the hottest hours of the day.
Time Outdoor Activity Around the Heat
Reschedule strenuous outdoor work or exercise to early morning or after sunset. Peak heat index typically hits mid-to-late afternoon, hours after the day's high temperature.
Hydrate Before You're Thirsty
Thirst is a lagging indicator of dehydration. Drink water steadily throughout a hot day rather than large amounts all at once, and cut back on alcohol and caffeine, which both accelerate fluid loss.
Get Heat Alerts on Your Phone
StormCast pushes Heat Advisories, Excessive Heat Watches, and Excessive Heat Warnings from the NWS the moment they're issued for your location.
