Wet Bulb Temperature: Swelter

Wet Bulb Temperature: Swelter

WBGT, Heat Index & Safety

24 ratings
2 reviews
Free
In-App Purchases

Details

Released
August 5, 2026
Updated
October 3, 2026

Features

Wet Bulb Temperature: Swelter screenshot #1 for iPhone
Wet Bulb Temperature: Swelter screenshot #2 for iPhone
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Wet Bulb Temperature: Swelter screenshot #8 for iPhone
Wet Bulb Temperature: Swelter screenshot #9 for iPhone
Wet Bulb Temperature: Swelter screenshot #10 for iPhone
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About

This app calculates the Wet Bulb Globe Temperature (WBGT) to assess outdoor heat risk for activities. It provides clear safety flags and hourly forecasts to help you plan outdoor events safely. Get personalized alerts and find the best times for your activities.

✓WBGT heat stress calculation
✓Hourly heat risk timeline
✓Best window for outdoor activity
✓Seven-day WBGT forecast
✓Severe heat and storm alerts
✓Home and lock screen widgets
✓Global location support
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What's New in Wet Bulb Temperature

1.6.0

October 3, 2026

MAJOR UPDATE Introducing a brand new Apple Watch app. Swelter is now on your wrist, with a full companion app, watch face complications, and Smart Stack support. There is also a new Apple Watch screen in Settings where you can check sync status, troubleshoot, and see details about how the watch app works. Some complications and features are free, and some are part of Swelter Pro. - A beautiful Apple Watch app with full screen color gradients, bold typography, current WBGT guidance, and useful weather metrics at a glance. - Screens include: core WBGT guidance, Quick Metrics, Best Window, Heat Index / Feels Like / Wind Chill, UV Index, wind speed, precipitation, and sunrise/sunset. - Complications include small circles for WBGT and heat index, corner complications for analog watch faces, inline text complications, and a large complication for modular faces. - A Smart Stack widget shows current WBGT, the current verdict, and heat index/feels-like temperature at a glance. - This update also improves the icons and colors of the Air Temperature and Heat Index / Feels Like / Wind Chill readings in the app and widgets. They now follow the full temperature color spectrum, so the color always matches the current reading. The watch app runs a full copy of the same physics engine as the iPhone app and fetches Apple Weather data directly, so it keeps working on its own, away from your phone. If you run into any issues or have questions, email gavin@rbrn-labs.com or use Contact in the app. Thanks for using Swelter!

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Subscriptions & In-App Purchases

Swelter Pro Monthly

Every Swelter Pro feature, billed monthly.

$2.991 Month
How to cancel Wet Bulb Temperature subscription ⁉️

Events

Read more about Heat Safety on Your Wrist

Heat Safety on Your Wrist

Heat safety, UV, and weather for athletes.

Oct 4, 2026 — Nov 3, 2026

Read more about Siri Comes to Swelter

Siri Comes to Swelter

Ask Siri for the current heat risk outdoors.

Aug 31, 2026 — Sep 30, 2026

User reviews

Love this app!

Great work Swoog!

Helpful app

Gives me a better understanding of the best times to get outside to exercise or do yard work. The alert for high risk conditions is especially helpful.

Response from developer

Thanks for using Swelter, enjoy the time outdoors! 😎🐈

FAQ

What is Swelter's WBGT calculation based on?

Swelter calculates WBGT by considering air temperature, humidity, wind, and sun strength. This provides a more accurate measure of heat stress than air temperature and heat index alone.

Does Swelter have ads?

No, Swelter does not contain advertisements. The app is supported entirely by Swelter Pro subscriptions.

What features are included in Swelter Pro?

Swelter Pro unlocks full week charts, hourly UV and precipitation data, additional alert types, year-over-year trends, saved locations, and the complete widget set. Free users retain core safety features.

How accurate is Swelter's WBGT data?

Swelter is validated against a large network of WBGT stations, with 99.94% of readings within one flag level compared to 10,760 station-hours of data.

What is the age rating for Swelter?

Swelter has an age rating of 12+, making it suitable for users aged 12 and older.

How often is Swelter updated?

Swelter was last updated on August 6, 2026, with the latest version being 1.1. This indicates regular maintenance and potential feature additions.

What devices does Swelter support?

Swelter is available for iPhone and iPad devices, allowing users on Apple's mobile platforms to access its heat safety features.

What are the subscription options for Swelter Pro?

Swelter Pro offers monthly subscriptions at $2.99 per month and yearly subscriptions at $14.99 per year. The yearly plan includes a 7-day free trial.