How UV GO chooses your time outside
UV GO compares forecast windows inside your free hours and chooses the one with the lowest average score. The rules below are shared with the planner, so the threshold tables reflect the implementation.
From forecast to a recommendation
Only hours marked as daytime by Open-Meteo are eligible. Starts are on the hour. A 30-minute outing uses one full forecast hour; longer outings use consecutive hours. For today, the earliest start is the current time rounded up to the next hour.
Each hour receives points for UV, rain, heat, cold and wind. The window score is their average. Ties favour the milder worst hour, then the earlier start.
A worked example
Suppose two eligible two-hour windows have hourly scores of 2 and 4, and 3 and 3. Both average 3. The second window wins because its worst hour scores 3 rather than 4. These are illustrative scores, not a live forecast.
What the result cannot tell you
A forecast is not a live measurement. Missing factors add no points, so a low score can reflect incomplete data. The best available window can still be marked Not recommended. The score does not assess your personal medical risk.
All displayed times refer to the selected place. Forecast conditions may change. Check the current forecast before heading out and use your own judgement.
See the author and editorial approach, the UV index guide, or plan an outing.
How it works
Pick a place
Search for a city or use your current location. UV GO saves the selected place in your browser when storage is available.
Set your time
Choose today or tomorrow, the hours you are free, how long you will be out and what you will be doing.
Get one answer
When a daylight window fits, you see the lowest-scoring time, its verdict, a short explanation and suggested items to take. Even the best window can be Not recommended.
The rules behind the answer
Each forecast hour gets points for UV, chance of rain, heat, cold and wind. Lower is better. A window is scored as the average of its hours. UV GO compares the exact averages; ties go to the window with the lowest worst-hour score, then the earliest start.
Windows start on the hour and must fit inside your free time. Every included hour must be marked as daytime in the forecast. For today, starts before the current time are excluded: at 14:10, the earliest start is 15:00. All times use the chosen place’s local time.
A 30-minute outing needs a full hour inside your free time and uses the same forecast as a 1-hour outing, but its result ends after 30 minutes. Outings of 2 or 3 hours use 2 or 3 consecutive forecast hours. UV GO does not calculate daylight eligibility minute by minute from sunrise and sunset.
Active adds more heat points and always suggests water. Relaxed uses the standard points. Long in the sun increases UV points; duration is chosen separately.
UV
UV is rounded to the nearest whole number first, with .5 rounded up. For Long in the sun, UV points are multiplied by × 1.5.
| UV index | Points | Long in the sun |
|---|---|---|
| 0–2 | 0 | 0 |
| 3–5 | 2 | 3 |
| 6–7 | 4 | 6 |
| 8+ | 6 | 9 |
Rain
| Chance of rain | Points |
|---|---|
| Under 30% | 0 |
| 30–59% | 2 |
| 60%+ | 5 |
Heat, cold and wind
Heat and cold use the feels-like temperature, which includes wind and humidity.
| Factor | When | Points |
|---|---|---|
| Heat | Feels like 30°C or more | +3+5 for Active |
| Cold | Feels like below 0°C | +2 |
| Wind | Wind 40 km/h or more | +3 |
Verdict
The average window score is rounded to the nearest whole number, with .5 rounded up, then matched to a verdict. Hourly verdicts use that hour’s score. The best window can still have a red verdict.
| Window score | Verdict |
|---|---|
| 0–2 | Good |
| 3–5 | OK with protection |
| 6+ | Not recommended |
The short explanation
The reason line shows up to two factors that add the most points across the chosen window. It uses the highest available UV, chance of rain, heat or wind value, or the lowest feels-like temperature for cold. It describes the selected window; it does not compare it with other windows. When no factor adds points, it says “No points from available forecast data”.
What to take
The checklist uses the highest or lowest available values across the forecast hours of your best window. “No extra items suggested.” means none of these rules triggered with the available data.
| Item | Appears when |
|---|---|
| Sunscreen | The highest rounded UV in your window is 3 or more |
| Hat & sunglasses | The highest rounded UV in your window is 6 or more |
| Rain jacket | At least one hour has a 30% or higher chance of rain |
| Water | You picked Active, or at least one hour feels like 25°C or more |
| Warm layer | At least one hour feels like below 5°C |
Reading the forecast
Hourly shows all 24 hours. Switch between UV, chance of rain and feels-like temperature, and select an hour for its values and points. The shaded band marks your free time; the outline marks the forecast hours used for the best window. Your free time lists those hours with individual verdicts. A longer bar means more points, and Best marks hours in the chosen window. Those hourly verdicts can differ from the window’s average verdict.
Now shows the current hour’s forecast, rather than a live measurement. Tomorrow’s summary shows peak UV and the feels-like range across all forecast daylight hours, rather than just your chosen window. A dash or “no data” means a forecast value is missing. Missing factors add no points and cannot trigger checklist items, so a low score can reflect incomplete data.
When no window fits
Extend your free time or shorten the outing if it does not fit. If no daylight window fits, change the hours or duration. When a forecast loads and all eligible starts today have passed, UV GO switches to tomorrow. Choose Today again to keep viewing today for the rest of the session. Changing the plan recalculates the result immediately; Done closes the Plan panel.