Methodology · data year 2024
How Comfort Atlas scores outdoor weather
Comfort Atlas measures how much of the day you could spend outside without being too hot, too cold, rained on, or blown around. For each of 35 major US cities, we check every daytime hour in 2024 against a comfort rule and count the share that passes.
The default rule
An hour counts as enjoyable only if it passes every check below.
| Check | Default | Why |
|---|---|---|
| Time of day | 8 AM to 9 PM local | Cold pre-dawn hours shouldn't count against a city. |
| Feels-like temperature | 48–79°F UTCI (9–26°C) | The "no thermal stress" band of the Universal Thermal Climate Index. |
| Sun or shade | Either one in range | You can usually pick the sunny or shady side of the street. |
| Rain | 1 mm/h or less | Above this is steady rain, the kind you'd want an umbrella for. |
| Wind gusts | 12 m/s (27 mph) or less | Stronger gusts start scattering napkins and papers. |
None of these is sacred. Every one is a slider on the interactive map, and the ranking recomputes in your browser from the same hourly data.
Data sources
- ERA5 hourly reanalysis (Hersbach et al., 2020), produced by ECMWF for the Copernicus Climate Change Service. We use air temperature, dewpoint, 10 m wind, wind gusts, precipitation, and shortwave and longwave radiation at each city's coordinates for every hour of 2024. Dataset.
- The Universal Thermal Climate Index (Bröde et al., 2012), calculated with the open-source pythermalcomfort library. The sun and shade versions differ in how much radiant heat reaches you, which we derive from ERA5 radiation and the sun's position.
- PRISM 1991–2020 normals (PRISM Climate Group, Oregon State University), 4 km mean temperature. These are used only for the weather-escape filter, which asks how much cooler in summer or warmer in winter a short drive can get you. Dataset.
Limitations
- This is one year (2024) of weather, not a long-term climate average. An unusually warm or wet year moves a city's score.
- ERA5 grid cells are roughly 31 km across. That's fine for regional climate but blurs microclimates like coastal fog lines, urban heat islands, and valley inversions.
- Each city is one point. Big metros contain several climates; coastal and inland Los Angeles are very different places in August.
- Comfort is personal. The defaults use a standard physiological band, and the sliders are there for anyone who runs hotter or colder than that.
Open data
The default-settings results for every city, with monthly breakdowns, are in a CSV download. Each city also has its own page, starting with San Diego, CA.
About this project
Comfort Atlas is an independent project built from public climate data from ECMWF/Copernicus (ERA5) and Oregon State's PRISM Climate Group. It isn't affiliated with either. Found an error or want a city added? Use the Feedback button on the map.