How GoodDayTo judges exterior-painting weather
Exterior painting needs more than a moment without rain. GoodDayTo scores every hour in the selected one-, three- or five-hour job, then checks the next 12 continuous forecast hours for rain. Humidity, air temperature and wind also affect application and drying.
- Rain probability
- Measured precipitation
- Relative humidity
- Air temperature
- Wind speed
- Daylight
🎨 The product label still comes first
- At least 0.5 mm of forecast rain or a 70% probability in the 12 hours after the job caps the result at NOT TODAY.
- At least 0.1 mm or a 40% probability in that post-job period caps it at WAIT.
- Different paints, stains, primers and sealers have different application and drying limits.
- The wall, wood or metal surface can be hotter, colder or wetter than the reported air.
- Dew, overnight condensation and recent rain can matter even when the forecast currently looks dry.
Why GoodDayTo looks beyond the working hours
A dry application period is not enough if rain arrives while the coating is still setting. The score protects the complete selected work period and checks 12 more continuous forecast hours after it ends. It also penalises high humidity because slower evaporation can extend drying time, and it reduces the result as wind becomes strong enough to carry dust, leaves or overspray.
A WAIT result can mean conditions improve later in the day, but it can also mean that the post-job forecast does not stay reliably dry. Because the model uses a general weather screen, compare the suggested window with the application and drying conditions printed by the coating manufacturer.
A practical example
If a three-hour painting job stays dry but 0.6 mm of rain is forecast six hours after it ends, the post-job cap makes the result NOT TODAY even when the working hours alone look favourable. A complete dry 12-hour outlook leaves the weather score free to reach GO.
What temperature does the score prefer?
The model favours moderate temperatures rather than extreme heat or cold. That is intentionally broad because products differ. Direct sunshine can also heat a dark surface well above the air temperature, while shaded masonry can remain cool and damp. GoodDayTo does not pretend the forecast air temperature is the same as the surface temperature.
What the exterior-painting score cannot know
The app cannot measure substrate moisture, dew point at the wall, surface temperature, paint chemistry, number of coats, drying time, shade, dust, pollen or whether the surface was recently pressure washed. It also cannot tell whether a ladder or work area is safe. Treat the result as a weather filter that helps decide whether the day is worth considering, then follow the coating instructions and safe working practices.
What the score means
GO means the forecast has a promising dry, moderate and relatively calm working window. WAIT means conditions are mixed or a better period may arrive later. NOT TODAY means rain risk, humidity, temperature, wind or severe weather currently makes exterior painting a poor weather choice.
Frequently asked questions
What weather is best for exterior painting?
A useful dry spell, moderate temperature, lower humidity and lighter wind are generally more favourable than very hot, wet, humid or windy conditions.
Why can a dry hour still get WAIT?
GoodDayTo checks the complete selected job plus the next 12 continuous forecast hours. At least 0.5 mm of rain or a 70% probability caps the result at NOT TODAY; at least 0.1 mm or a 40% probability caps it at WAIT.
Does the score know whether the wall or timber is still damp?
No. A surface can remain damp after earlier rain or dew even when the forecast is now dry. Substrate moisture must be checked separately before painting.
Does wind matter for painting outside?
Yes. Strong wind can carry dust and debris onto wet coatings, affect spraying and speed up surface drying unevenly, so windy conditions reduce the score.
Does GO mean it is safe to apply any paint or stain?
No. Always follow the coating manufacturer’s temperature, humidity, drying-time and surface-preparation instructions. Product requirements override the general weather score.