A clean Garmin Connect IQ watch face that puts time, activity stats, and a barometric weather forecast on your wrist — no phone connection required.
The forecast engine is based on Raymond Sager's meteorological method (1960s, US Navy). Unlike simpler barometric forecasters, Sager treats wind direction as a primary forecast dimension alongside pressure and its trend.
Since a watch face has no compass input, wind direction is fixed to calm (octant 0). This makes the forecast purely pressure-driven — still effective for detecting approaching fronts, but without the directional refinement available in the companion widget (SimplyWeather).
Inputs (all derived on-device):
- Current barometric pressure (hPa)
- Pressure trend over the last ~3 hours (rising / steady / falling)
- Current month (for seasonal corrections)
- Hemisphere (north / south, via GPS with Northern fallback)
How it works:
- Three lookup tables (
steadyBase,risingBase,fallingBase) produce a base forecast number (0–25). - The base number is adjusted by pressure level (±2) — high pressure biases toward fair, low toward unsettled.
- A seasonal modifier (±1) accounts for summer convective storms and winter clearing patterns.
- The final forecast number maps to a condition label (e.g. "Fairly fine, showers likely") and a precipitation probability (0–95%).
26 forecast conditions range from Settled fine (0) to Stormy, much rain (25).
On top of the standard trend, the engine computes the second derivative of pressure (P″) using three hourly samples captured during the single-pass pressure iteration:
A 0.15 hPa deadband filters sensor quantisation noise. Three refinement rules modify the trend input to Sager before the forecast lookup:
| Condition | Rule | Effect |
|---|---|---|
| Trend is steady, P″ ≤ −0.5 | Upgrade to falling | Early storm warning — pressure drop is accelerating before the 3 h window catches it |
| Trend is falling, P″ > +0.5 | Downgrade to steady | Front is passing — pressure deceleration means conditions are stabilising |
| Trend is rising, P″ ≤ −1.0 | Keep rising (no flip) | Noise filter — prevents a sensor glitch from overriding a genuine high-pressure build |
Hourly samples are captured by index proximity (sample 12 ≈ −1 h, sample 24 ≈ −2 h at ~5 min spacing) with a ±35 min tolerance window.
Barometric forecasting precision varies by terrain and weather pattern. Without wind direction input, accuracy is slightly lower than the companion widget:
| Scenario | Accuracy | Lead time | Notes |
|---|---|---|---|
| Urban / lowland | ~75% | 2–4 h | Stable environment, pressure patterns read cleanly; acceleration catches convective buildups 30–60 min earlier |
| Mountain hiking (1500–2500 m) | ~60% | 1–3 h | Altitude thermals and terrain-funnelled winds add noise. Always cross-check official mountain forecasts. |
| Coastal / seaside | ~80% | 3–6 h | Flat terrain, clean pressure gradients — best case for barometric forecasting. Fronts approach predictably. |
Large, easy-to-read digital time in the centre of the display with the full date (Thu, 20 Feb 2026) just below.
| Stat | Description |
|---|---|
| Steps | Daily step count (in thousands), shown with an icon |
| Distance | Daily distance (in km), shown with an icon |
| Notifications | Unread notification indicator at the top of the screen |
| Battery | Estimated battery life remaining in days |
- Forecast text — a short condition such as Settled fine, Changeable, showers likely, or Stormy, much rain, with a precipitation probability percentage when applicable.
- Weather icon — context-aware by time of day and season (see table below).
- Hemisphere-aware — automatically detects your hemisphere via GPS and adjusts seasonal corrections accordingly.
- Refresh cycle — the forecast recalculates every 3 hours to balance accuracy with battery life.
The watch face selects an icon based on three inputs: the Sager forecast number, time of day, and season.
Day / night is determined by a fixed 07:00–19:00 window.
Season is hemisphere-aware — Northern: Dec–Feb = cold season; Southern: May–Sep = cold season.
| Forecast | Condition | Warm season | Cold season |
|---|---|---|---|
| 0–1 | Clear / fine | ☀️ Sun (day) / 🌙 Moon (night) | ☀️ Sun (day) / 🌙 Moon (night) |
| 2–6 | Fair / variable | 🌤 Cloud-day / ☁️🌙 Cloud-night | 🌤 Cloud-day / ☁️🌙 Cloud-night |
| 7–21 | Showers → rain | 🌧 Rainy | 🌨 Snowy |
| 22–25 | Stormy | ⛈ Thunderstorm | 🌨❄️ Snowstorm |
Note: unlike the companion widget, bands 7–21 are grouped into a single rain/snow icon (no day/night or light/heavy variants) to keep the watch face clean.
- Garmin Fenix 8 Solar (47 mm)
Requires Connect IQ API 5.1.0 or later. Additional devices can be added via
manifest.xml.
| Permission | Reason |
|---|---|
| SensorHistory | Read barometric pressure history to calculate pressure trends |
| Positioning | Detect hemisphere (north/south) for seasonal corrections |
| Notifications | Show unread notification count on the watch face |
Build with the Garmin Connect IQ SDK and side-load the .prg file to your watch.
- Clone or download this repository.
- Open the project in Visual Studio Code with the Monkey C extension.
- Build for your device (
Monkey C: Build for Device). - Copy the generated
.prgfile to your watch'sGARMIN/APPSdirectory.
- Connect IQ SDK 5.1.0+
- Visual Studio Code with the Monkey C extension
# Build via the VS Code command palette:
# Monkey C: Build for Device
# or use the Connect IQ CLI:
monkeyc -f monkey.jungle -o SimplyWatch.prg -d fenix8solar47mmsource/
SimplyWatchApp.mc # Application entry point
SimplyWatchView.mc # Watch face layout, rendering & pressure logic
SimplyWatchForecast.mc # Sager Weathercaster forecast engine
resources/
drawables/ # SVG icons (weather, battery, steps, etc.)
strings/ # App name
forecast-strings/ # Forecast condition descriptions (26 outcomes)
- Sager Weathercaster: Based on Raymond Sager's barometric forecasting method (1960s, US Navy)
- Icon design: Freepik from Flaticon, licensed under CC BY 3.0
This project is licensed under the MIT License — see the LICENSE file for details.