Heat stress in Fontana
Sun-baked Inland Empire flats see extended summer hot spells that keep outdoor heat stress high.
Reduce exertion and hydrate frequently. Take regular breaks somewhere cooler.
Wet-bulb globe temperature via the Liljegren (2008) method. This page is cached and refreshes in the background, so the live badge below can be a few minutes ahead of it.
View Fontana on the live mapReading heat stress in Fontana
Wet-bulb globe temperature (WBGT) is the heat measure that actually tracks danger to the body. Unlike the plain air temperature on your phone, it folds in humidity, wind, and direct sun: the factors that decide whether your sweat can still cool you. It’s the standard the military, athletic associations, and occupational-safety bodies use to call when outdoor activity is no longer safe.
That matters in Fontana because sun-baked Inland Empire flats see extended summer hot spells that keep outdoor heat stress high. The number above is the live outdoor WBGT for the city right now; tap through to the live map to inspect any neighborhood, scrub the forecast hour by hour, and see the 7-day outlook.
How hot Fontana usually gets
Across 2015–2024, Fontana averaged a 93°F daily high in summer: 31st hottest of the 174 metros we track, and August is typically the warmest month.
August is the hard part of a long season: roughly 21 days a year pass 100°F, inside about 95 above 90°F.
At about 48% summer humidity, the air is damp enough to blunt how well sweat cools you on the worst afternoons.
The ceiling is a long way above the routine: the hottest day in this sample hit 115°F, about 22°F past a normal summer afternoon.
Daily high temperatures and humidity from ERA5 reanalysis, 2015–2024 (hottest day in the sample: 2020-09-06). These are climate averages for context: the reading at the top of this page is the live one.
Heat in Fontana: common questions
How hot does it usually get in Fontana?
Across 2015–2024, Fontana averaged a 93°F daily high through summer, with about 95 days a year at or above 90°F and 21 at or above 100°F. August is typically the hottest month, and the hottest day in that sample reached 115°F. Figures are from ERA5 daily reanalysis.
When is the hottest time of year in Fontana?
August has the highest average daily high in Fontana. Summer humidity averages about 48%, enough to blunt how well sweat cools you on the hottest afternoons. Use the forecast on this page to plan around the specific days that matter.
What is the WBGT in Fontana right now?
The reading at the top of this page is the current wet-bulb globe temperature for Fontana, California, computed from live weather by the Liljegren (2008) method and labeled with how recently it updated. For an exact reading at your own neighborhood, plus an hour-by-hour forecast, open the live map.
Why is WBGT more useful than the temperature for Fontana?
Air temperature ignores humidity, wind, and sun: the things that decide whether heat is dangerous. Fontana's climate (sun-baked Inland Empire flats see extended summer hot spells that keep outdoor heat stress high.) is exactly why a single "feels-like" or thermometer reading can understate the real risk. WBGT captures all of it in one number.
When is heat most dangerous in Fontana?
August is the peak month in Fontana, and within a day heat stress is highest in the early-to-mid afternoon when sun load is greatest. With roughly 21 days a year above 100°F, the safe window is often early morning rather than merely "not midday". Use the forecast on this page to find the window that works.
Put Fontana’s live heat stress on your site
A self-updating WBGT badge for schools, teams, camps, and local sites: it always shows the current reading and links back here.
<iframe src="https://wetbulbtracker.com/embed/fontana-ca" width="340" height="150" style="border:0" title="Live WBGT: Fontana, CA" loading="lazy"></iframe>Paste it into any website. The badge updates itself and links back here. Add ?theme=light for light sites.