About Autumn Guide

There are foliage trackers across the globe, but none of them bring the world together. Autumn Guide's goal is to celebrate, nurture, and help people around the world learn about the season that takes over twice a year.

Who makes this

Benjamin Janes builds and runs Autumn Guide. He is a software developer, not a forester. The forecast is a phenology model driven by ERA5 weather data, calibrated against published peak dates and checked each season against photographs and state foliage reports. Nobody else is behind the curtain, so mistakes on this site are his.

Code and open work live on GitHub. Corrections and questions go to hello@autumnguide.com.

How the model works

Daily temperatures from the ERA5 weather reanalysis (via Open-Meteo) feed a phenology model that weighs day length against accumulated autumn cooling, with an early hard frost able to yank the peak forward on its own. Elevation shifts it again, by roughly a day for every 300 meters. Slide the slider on the tracker and watch fall color move. The full method, the daily rebuild, and the per-region corrections are written up on the methodology page.

How we check it

Weather alone does not tell the whole story. Seattle and Duluth sit at nearly the same latitude with September temperatures that agree within a degree, yet Duluth's birches and aspens turn three weeks before Seattle's maples. Most of that gap comes down to how wide the seasonal temperature swing is, which the model now reads directly. Whatever is left gets absorbed by a per-region shift fitted against published peak dates.

Scored against 103 published peak windows over four weather years, and with those per-region shifts switched off, the model lands about five days from the published window on average. It does better in North America (3.5 days across 62 locations) than in Europe (7.2 days across 41, where the reference data is tourism-grade and the Alps are worse still). Those constants were fitted against the same reference set, so read the numbers as in-sample rather than as a clean out-of-sample test. If you catch the map running early or late where you live, send a date and a photo and it gets looked at.

Data & thanks

Weather data by Open-Meteo.com (CC BY 4.0), built on ERA5 from the Copernicus Climate Change Service. Base maps by OpenFreeMap and OpenStreetMap contributors. Elevation from Mapzen/USGS terrain tiles. Region boundaries derived from Natural Earth (public domain). Thank you to these projects for helping support our modeling.