About Thermograph
Thermograph answers one question for any point on Earth: how unusual is this weather? Instead of an absolute temperature, it shows where a day falls in that exact location's own climate history.
Where the data comes from
The ~45-year daily record (high, low, feels-like, humidity, wind, gust and precipitation) comes from the ERA5 reanalysis (ECMWF), served via Open-Meteo. Because reanalysis is a gridded, model-consistent record, Thermograph works even where there's no weather station, anywhere on the ~4 sq mi grid.
How a day is graded
For each metric and date, Thermograph builds a reference distribution from every historical day within ±7 days of that day-of-year, a 15-day seasonal window across all years. The observed value is placed on that distribution as an empirical percentile, then mapped to a grade from “Below Normal” through “High” to “Near Record”.
Everything is relative to the location: a 60°F day can be “Above Normal” in one place and “Below Normal” in another. Precipitation is graded only among days that actually rained, so “Heavy” means heavy for a rainy day here. See the grade guide for the full scale.
Freshness
The historical archive updates as new days are added; recent and forecast conditions refresh hourly. City climate pages show the latest recorded day graded against the local normal.