🌡 Heat Wave Probability Calculator

What Is a Heat Wave?

A heat wave is generally defined as a period of at least two to three consecutive days where daily high temperatures significantly exceed the historical average for a given location. There's no single national threshold — what counts as a heat wave in a typically mild city can be an ordinary summer week somewhere hotter. That's why this calculator builds a threshold specific to your selected city rather than applying one number nationwide.

How Heat Wave Probability Is Calculated

This tool analyzes 20 years of historical daily temperature records for your city to establish a local heat wave threshold, historical average, and past heat wave frequency. It then combines that baseline with current seasonal conditions to estimate the probability of a heat wave occurring at some point this season. Select your state and city above and press Calculate Heat Wave Probability to see your city's numbers, including historical average temperature, total past heat waves, the longest streak on record, and the most recent heat wave year.

Heat Wave Prep Checklist

• Stay hydrated — increase water intake before and during heat wave conditions, even without noticeable thirst.
• Limit peak-hour exposure — schedule outdoor work or activity for early morning or evening rather than mid-afternoon.
• Check on vulnerable people — older adults, young children, and those with chronic conditions are at higher risk.
• Plan for power outages — heat waves increase strain on the power grid; know a backup plan if air conditioning goes out.
• Know the warning signs — heavy sweating, dizziness, nausea, and headache can indicate heat exhaustion and should not be ignored.

Checking the humidity side of the equation? Try the Heat Index Calculator to see the feels-like temperature for today, or check the Snow Day Calculator once winter rolls around. More guides are on the Weather Blog.

Frequently Asked Questions

What counts as a heat wave?

A period of at least two to three consecutive days where daily highs significantly exceed the historical average for that specific location.

How is heat wave probability calculated?

By analyzing 20 years of historical daily temperature data for your city to establish a local threshold, then combining that with current seasonal conditions.

Why does the heat wave threshold differ by city?

Thresholds are relative to what's normal locally — a city with a mild climate can hit heat-wave-level stress at a lower absolute temperature than a naturally hotter city.

How should I prepare for a heat wave?

Stay hydrated, avoid peak-afternoon outdoor exposure, check on vulnerable neighbors, plan for possible power outages, and know the signs of heat exhaustion and heat stroke.

Is heat wave probability the same as a weather forecast?

No — a forecast predicts short-term conditions days out. This calculator estimates the statistical likelihood of a heat wave this season based on long-term historical patterns.