About & Methods
What this site is, what it refuses to do, and where every number on it comes from.
What this is
Forecast Season reads the world's operational seasonal forecast systems — one month ahead to seven — for three audiences: the United States, Europe, and the globe.
It is the seasonal member of the Forecast Network, which is a family of weather and climate sites that share one idea: that the American Interstate system is the best interface ever designed for showing a stranger, at speed, where they are and where they can go next. Green means wayfinding. Blue means services. Brown means the interesting detour. Red means pay attention. Those roles do not move from site to site, which is why the network reads as one thing.
This site's route is Interstate 90 — the longest run in the system, Seattle to Boston, 3,020 miles. Seasonal forecasting is the long haul.
What it will not do
The commitmentsNo.1
No invented data
Nothing on this site is a placeholder that looks like a forecast. A route that is not built is signed surveyed or paving and shows you nothing. The only live numbers on the home page today are astronomical and calendrical, and both say so on the page.
No.2
No map without its skill
A seasonal anomaly map is meaningless without knowing whether the model has any skill for that variable, that region, that season and that lead. Route 06 exists so that every map on this site can be read next to its own verification.
No.3
No blending of streams
Reanalysis is reanalysis, model climatology is model climatology, and a forecast is a forecast. A SEAS5 anomaly is a departure from SEAS5's own hindcast, not from ERA5, and this site will always say which baseline it is using.
No.4
Not an official forecast
The official outlooks belong to NOAA CPC, the national meteorological services and ECMWF. This site reads them and reads the models under them. For a decision that matters, go to the source — every one of them is linked.
Sources
Named, and linkedECMWF SEAS5
The reference seasonal system; 51 members to seven months.
Copernicus C3S
The multi-system seasonal archive, and the CDS the data comes from.
NMME
The North American Multi-Model Ensemble, hosted by NOAA CPC and the IRI.
NOAA CPC
The official US monthly, seasonal and drought outlooks.
ERA5
The reanalysis every anomaly on this site is ultimately measured against.
IRI
Hindcast skill, ENSO plumes, and the seasonal-forecast literature.
Colophon
Static site, generated by a small Python program with no build step and no JavaScript framework. Type is Overpass and Overpass Mono — Overpass is derived from Highway Gothic, the typeface on the signs this whole theme is borrowed from. The Interstate shield is the real FHWA blank, drawn from the MUTCD outline rather than approximated with a rounded rectangle; Europe's lane wears a UNECE E-road plate, and the global lane a meridian roundel.
The season clock is computed from Jean Meeus, Astronomical Algorithms, chapter 27 — the mean-instant polynomial plus its 24 periodic terms, accurate to well under a minute. It is the only thing on the front page that changes by itself, and it is astronomy, not a forecast.
Built and run by Ryan Maue. Supported by Substack subscribers.