How GoodDayTo judges outdoor swimming weather
The score evaluates the air weather around the swim: temperature, rain risk, sustained wind, gusts, UV and useful daylight. It favours milder or warmer air, lower rain risk and lighter wind because those conditions generally make changing, entering and leaving the water more comfortable. High UV is treated as a caution because time beside the water can add significant sun exposure.
This deliberately is not a water-safety score. The same air forecast can sit above a warm supervised pool, a cold quarry, a fast river or rough coastal water. GoodDayTo cannot merge those very different environments into one honest number.
- Air temperature
- Rain probability
- Wind and gusts
- UV exposure
- Daylight
- Mapped swimming places
🏊 The water always gets the final vote
- GoodDayTo does not measure water temperature, current, tide, waves, depth, water quality or blue-green algae.
- A warm sunny day can still have dangerously cold water, especially in spring, deep lakes, rivers and coastal areas.
- Only swim where access is permitted and where your ability, supervision, equipment and local warnings make the location appropriate.
Why wind and daylight matter
Wind can increase evaporative cooling after a swim and can make open water rougher, but GoodDayTo only sees the surface air forecast, not wave height or current. Stronger wind therefore lowers the weather score without pretending to calculate water state. Daylight is strongly preferred because visibility, entry and exit points, other water users and supervision are easier to assess.
A GO result means the air-weather layer looks favourable enough to consider the activity. It never means the water itself has been cleared as safe.
Finding a place to swim
Local Fit can look for mapped outdoor swimming areas or explicitly mapped outdoor pools. Mapping quality varies, and a place can be seasonal, closed, private, unsupervised or unsuitable despite appearing on a map.
Before entering, verify whether swimming is allowed and check official local information for water quality, contamination, temperature, currents, tides, depth, lifeguard cover and temporary warnings.
Reading GO, WAIT and NOT TODAY
GO means the forecast factors GoodDayTo can genuinely measure look favourable for this activity during the suggested window. WAIT means conditions are mixed or another upcoming period looks meaningfully better. NOT TODAY means the weather layer itself is currently a poor fit. These are planning recommendations, not guarantees, bookings or safety clearances.
Frequently asked questions
Does the score include water temperature?
No. It only uses air-weather inputs. Water temperature must be checked from an appropriate local source or at the venue.
Can GO mean open water is safe?
No. Currents, tides, waves, depth, water quality, cold-water shock and supervision are outside the weather score.
Why can high UV lower the score?
Swimming often includes time on the shore, poolside or in reflective sunlight, so strong UV increases exposure even when the air feels pleasant.
Can GoodDayTo find an outdoor swimming place nearby?
It can look for mapped swimming areas and outdoor pools where OpenStreetMap data is available, but it cannot confirm opening, access or safety.
Is this useful for sea swimming?
Only as an air-weather screen. Sea swimming also requires marine conditions, tides, swell, currents, water temperature and local warnings.