What it checks
- Heat: temperature, feels-like temperature and dew point, because sticky air stops sweat from cooling you. Long runs get stricter limits.
- Cold: wind chill, ice risk, and the cold-rain-and-wind mix behind most running hypothermia.
- Wind: sustained wind and gusts, with stricter limits on exposed waterfront routes.
- Precipitation: chance and estimated amount of rain or snow, plus thunder, freezing rain, sleet and heavy snow as hard stops.
- Visibility: fog and heavy rain.
- Daylight: sunrise and sunset computed locally, so you know when a run ends in the dark.
- Official alerts: active National Weather Service alerts for US locations.
How windows are scored
The rules are deliberately simple and fully published. Each start time gets one of four ratings: good conditions, fair conditions (something will make the run harder; the reasons say what), poor conditions, or forecast incomplete. Hazards always win: no preference can turn a thunderstorm into a “go”. Within the same rating, windows are ranked by how far the temperature is from a 45–55°F sweet spot, dew point, wind, gusts, rain chance and minutes of darkness, so the best start rises to the top. The research behind every number is on running weather science.
- A planning guide built from published sports-science and weather-safety research, not a guarantee. Forecasts can be wrong.
- All times use the selected location's time zone. Your time range controls when you start; the run may finish after the latest start.
- Every overlapping forecast hour is checked through your full distance and a 15-minute buffer, including a partial final hour. Start times are compared every 30 minutes.
- Good conditions: none of the checks below were triggered. Fair conditions: something will make the run harder or less comfortable; the reasons say what. Poor conditions: a limit we do not recommend running past. Forecast incomplete: we could not check everything.
- Poor at air temperature ≥95°F, feels-like ≥100°F, air temperature ≤10°F or feels-like ≤-18°F (frostbite risk in about 30 minutes).
- Poor at sustained wind ≥25 mph or gusts ≥30 mph (≥25 on waterfront routes). Missing gust forecasts are estimated at 1.5× the wind speed, never treated as calm.
- Poor when thunderstorms are forecast with “Chance” wording or stronger, or with a rain chance ≥40%; “Slight Chance” or “Isolated” thunder is fair on park routes and poor on waterfront routes.
- Poor for freezing rain, sleet, ice pellets, heavy snow or blizzard; for 40°F or colder with rain likely and wind ≥15 mph on runs over 60 minutes; and for dense fog with 10+ minutes of darkness.
- Official NWS alerts are matched by name: warnings for tornadoes, severe storms, flash floods, extreme heat or cold, winter storms and high wind are poor; advisories and watches are fair; coastal flood, surf and rip current alerts are poor on waterfront routes only.
- Fair at air or feels-like ≥80°F, or dew point ≥65°F (sticky; ≥70°F very muggy). Runs over 90 minutes use lines 5°F lower. Dew point, not relative humidity, is the moisture signal.
- Fair at sustained wind ≥15 mph (≥13 waterfront) or gusts ≥20 mph (≥18 waterfront).
- Fair at rain chance ≥70%, or ≥60% with ≥0.10 inch expected during the run, or ≥0.25 inch in an hour. Lower chances are shown as a note.
- Fair for cold rain (≤50°F with rain likely; 5°F warmer for runs over 90 minutes or slower than 12 min/mile), feels-like ≤14°F, or ≤32°F with precipitation possible. Dry cold above that gets a dress-warmly note.
- Fair for snow, fog or heavy rain in the forecast, patchy fog in the dark, or 10+ minutes of the run in the dark: before dawn or after dusk, the ends of civil twilight. The half-light between dawn and sunrise, or sunset and dusk, is noted but does not change the rating.
- Ranking among windows with the same rating: distance from a 45–55°F sweet spot, dew point above 55°F, wind (weighted by its square, as headwind cost grows), gusts above the sustained wind, rain chance and minutes of darkness, averaged over the time you are out.
- UV index comes from Open-Meteo for every location (NWS hourly forecasts do not include it) and is shown with sun-protection advice from 6 (high). It never changes a rating.
- Missing temperature, humidity, wind, rain chance or descriptions, or incomplete or stale forecasts, give "Forecast incomplete" instead of a rating.
- If US alerts cannot be verified during a routine outage, the window is rated fair with that reason. Outside the US, official alerts are not supplied; check your local weather service.
Where the weather comes from
US forecasts, station observations and alerts come from the National Weather Service API. Outside the US, model forecasts come from Open-Meteo (CC BY 4.0), labelled as model data; official alerts are not available there, so every international recommendation says to check the local weather authority. The UV index for every location, including the US, comes from Open-Meteo because NWS hourly forecasts do not carry it. Place search uses Open-Meteo geocoding with GeoNames data. If a source is missing or stale, the app says so instead of inventing a number.
Free, and funded by ads
PuddleRunner will always be free for runners. To pay for forecasts and hosting, we plan to show clearly labelled advertising. Ads will never sit between your question and the answer, never appear inside an alert, and are governed by your privacy choices.
What we will not do
- Store your location, postal code or coordinates on our servers.
- Require an account to plan a run.
- Present a forecast as a safety guarantee.
Who runs this
PuddleRunner. Questions, corrections and ideas: [email protected].