# Wet Bulb Temperature: Swelter — WBGT, Heat Index & Safety > Calculates WBGT heat stress for outdoor activity safety. (iPhone/iPad app by RBRN Labs LLC.) - Source: https://appshunter.io/ios/app/wet-bulb-temperature-swelter/id6794481096 (this page in markdown: same URL + `.md`) - Developer: [RBRN Labs LLC](https://appshunter.io/developer/6794481098) - Category: Weather, Health & Fitness - Price: Free with in-app purchases - Rating: 5.00/5 from 24 App Store ratings · 2 written reviews indexed - Age rating: 4+ - Requires: iOS 17.0 · 12 MB - Languages: American English - Released: 2026-08-05 - Data updated: 2026-10-05 - Monetization: freemium - User reviews in markdown: https://appshunter.io/ios/app/wet-bulb-temperature-swelter/id6794481096/reviews.md ## What is Wet Bulb Temperature? How risky is today's heat? Swelter tracks the WBGT, wet bulb temperature, and heat index hour by hour, finds the best window in your day, and alerts you before extreme heat arrives. Validated against 20k+ hours of station data. Your local conditions become one of four flags: GOOD TO GO, CAUTION, HIGH RISK, or CANCEL. The flags follow the American College of Sports Medicine's published WBGT thresholds, a scale built for heat safety during outdoor exertion in the sun. The heat index tells you how hot it feels in the shade. WBGT (wet-bulb globe temperature) also counts direct sun and wind, so it reflects how well your body can actually cool itself. It is the standard measure of heat stress, used worldwide for decades to decide when to limit outdoor activity. Swelter computes it on your phone from Apple Weather data. Built for runners, hikers, coaches and athletes, outdoor workers, and anyone planning a day in the heat. WHAT SWELTER DOES - Today: the current flag, the WBGT behind it, and an hour-by-hour timeline - Best Window: the least risky stretch of your day for a run, practice, or a shift outdoors - Week Ahead: seven days of hourly WBGT, plus a 10 Day Forecast for spotting heat waves - Alerts: a heads-up before extreme heat and storms arrive - Widgets: your flag and timeline on the home and lock screen - Any location worldwide, in its own local time - Siri & Shortcuts: ask for the current heat risk or build your own automations Also at a glance: NWS heat index, air temperature, wet bulb temperature, humidity, UV index, wind, precipitation and storms, sunrise and sunset. When building Swelter's WBGT algorithm, we validated it against over 20,000 hours of weather station data from the world's largest WBGT monitoring network in Japan. The full methodology and sources are documented in the app. Swelter is private by design: no account, no advertisements, and your data is never sold. Your location is used only to retrieve Apple Weather data. Try Pro free for 7 days with the yearly plan. Pro unlocks full week charts, the 10 day forecast, hourly UV and precipitation, extra alert types, saved locations, and year-over-year trends. Free users keep the core read: today's flag, the gauge, the timeline, current conditions, and severe-heat and storm alerts. Swelter is a planning tool, not a medical device. Its readings are estimates from weather data, not measurements from a physical device. Conditions can change quickly. When in doubt, choose the cooler option and use your best judgment. Weather data provided by Apple Weather. Terms of Use (EULA): https://rbrn-labs.com/swelter/terms/ Privacy Policy: https://rbrn-labs.com/swelter/privacy-policy/ ## Key features - 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 ## Pricing and in-app purchases Base price: Free. **Subscriptions** | Subscription | Price | Period | | --- | --- | --- | | Swelter Pro Monthly | $2.99 | per month | | Swelter Pro Yearly | $14.99 | per year | **One-time purchases** | Purchase | Price | Type | | --- | --- | --- | | Swelter Pro Lifetime | $39.99 | one-time | ## Is Wet Bulb Temperature safe? Not enough ratings yet to assess Wet Bulb Temperature. ## Is Wet Bulb Temperature legit? Wet Bulb Temperature: Swelter has limited verification signals. The AppsHunter Legitimacy Score for Wet Bulb Temperature is 58 out of 100 points across 7 verification signals from App Store and developer data. ## Recent user reviews (2 of 2) All indexed reviews: https://appshunter.io/ios/app/wet-bulb-temperature-swelter/id6794481096/reviews.md ### 5/5 — Love this app! *2026-08-31* Great work Swoog! ### 5/5 — Helpful app *2026-08-19* 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. **Developer response:** Thanks for using Swelter, enjoy the time outdoors! 😎🐈 ## Frequently asked questions about Wet Bulb Temperature ### 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. ## Version history (last 5 releases) ### 1.6.0 — 2026-10-03 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! ### 1.5.8 — 2026-09-29 Bug fixes and improvements. - Fixed a visual glitch where the animated background could briefly jump when navigating back from the Tomorrow screen. The background effects now fade out and back in cleanly during navigation. ### 1.5.7 — 2026-09-25 New in version 1.5.7: - Wind card (Pro): view current wind conditions, speed of wind gusts, direction the wind is blowing from, and the direction you are facing; powered by the built-in compass/magnetometer. ### 1.5.6 — 2026-09-24 MAJOR UPDATE Our largest update yet. New features, plus design and performance improvements. New in version 1.5.6: - Share button: Spotted some interesting weather conditions? You can now tap the "Share" button in the top left nav bar to generate a light or dark mode image of today's forecast and save it to your photo gallery, or share with your friends via iMessage. - If you prefer a cleaner look, you can also disable this Share button in Settings > Appearance > Hide Share Button (Pro) New in version 1.5.5: - Tomorrow View (Pro): the full detailed Today screen, for tomorrow. The gauge, the timeline, and every chart for the day ahead. Simply hit the “>” button in the top left nav bar. - Today's Pressure (Pro): a new barometric pressure chart with a Rising/Falling/Steady indicator and your choice of inHg or hPa. - The WBGT chart on the Week screen is now free for all users. - The Today screen now dims past hours, so you can see where "Now" is at a glance. - Rebuilt the rain animation from the ground up. It's smoother, more realistic, and runs at 120hz on supported devices. - New Appearance option (Pro): disable the rain, thunder, and snow effects while keeping the ambient background. - Week chart improvements (Pro): cleaner 2-hour scale, color gradients under the lines, and fixed bugs with chart layout. - Performance improvements (found and fixed bugs using profiler). Redesigned the “Pro” lock for free users, the gaussian blur was causing performance issues, we now use a simpler cover design. Questions or ideas? Email gavin@rbrn-labs.com or use Contact in the app. Thanks for using Swelter! ### 1.5.5 — 2026-09-24 MAJOR UPDATE Our largest update yet. New features, plus design and performance improvements. - Tomorrow View (Pro): the full detailed Today screen, for tomorrow. The gauge, the timeline, and every chart for the day ahead. Simply hit the “>” button in the top left nav bar. - Today's Pressure (Pro): a new barometric pressure chart with a Rising/Falling/Steady indicator and your choice of inHg or hPa. - The WBGT chart on the Week screen is now free for all users. - The Today screen now dims past hours, so you can see where "Now" is at a glance. - Rebuilt the rain animation from the ground up. It's smoother, more realistic, and runs at 120hz on supported devices. - New Appearance option (Pro): disable the rain, thunder, and snow effects while keeping the ambient background. - Week chart improvements (Pro): cleaner 2-hour scale, color gradients under the lines, and fixed bugs with chart layout. - Performance improvements (found and fixed bugs using profiler). Redesigned the “Pro” lock for free users, the gaussian blur was causing performance issues, we now use a simpler cover design. Questions or ideas? Email gavin@rbrn-labs.com or use Contact in the app. Thanks for using Swelter! Note: If you see "No Pressure Data" on the new Pressure card, this will become available once your 5 minute local cache passes (the "Updated" time on the top left of the Today screen). ## Apps similar to Wet Bulb Temperature | App | Rating | Price | Category | | --- | --- | --- | --- | | [Wet Bulb Temperature: WBGT](https://appshunter.io/ios/app/wet-bulb-temperature-wbgt/id6794531164) | 5.0 (13) | Free | Weather | | [Wet Bulb & Safety: HeatCue](https://appshunter.io/ios/app/wet-bulb-and-safety-heatcue/id6790204017) | 4.7 (15) | Free | Weather | | [HeatSafe WBGT](https://appshunter.io/ios/app/heatsafe-wbgt/id6781332510) | 3.0 (2) | Free | Weather | | [WetBulbCast](https://appshunter.io/ios/app/wetbulbcast/id6761316594) | 5.0 (1) | Free | Weather | | [Klimo WBGT](https://appshunter.io/ios/app/klimo-wbgt/id6745461795) | 4.1 (9) | Free | Weather | | [Heat Index: NIOSH Calculator](https://appshunter.io/ios/app/heat-index-niosh-calculator/id6760123940) | 4.4 (19) | Free | Weather | ## Related topics [trappers fanatic](https://appshunter.io/ios/topics/trappers-fanatic) · [temptracker india](https://appshunter.io/ios/topics/temptracker-india) · [temperature alerts](https://appshunter.io/ios/topics/temperature-alerts) · [heatstroke](https://appshunter.io/ios/topics/heatstroke) --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-10-05.*