Europe
The Copernicus multi-system, SEAS5 in full, and the awkward truth about forecasting a European winter. Being paved — the reference routes below are open now.
What this lane will carry
Route 01 · Route 03Multi-system
Copernicus C3S
Eight centres — ECMWF, the Met Office, Météo-France, DWD, CMCC, NCEP, ECCC and JMA — regridded onto one grid with one calendar and one hindcast period. Europe has the best-organised seasonal archive in the world, and this lane is built on it.
Reference
SEAS5, in detail
All 51 members, seven monthly leads, and the evolution of the outlook for one target month across successive initialisations — which is usually more informative than any single run of it.
Winter
The NAO problem
The European winter lives and dies on the North Atlantic Oscillation, and the models predict it with a signal that is real but far too quiet relative to their own spread. Any honest European winter product has to deal with this explicitly. Ours will.
The signal-to-noise paradox
Why European winters are strangeTake a large seasonal ensemble, average it, and correlate that ensemble mean against the observed winter NAO. You get a respectable correlation — the models know something. Now correlate one member of the ensemble against the rest of the ensemble. You get a lower correlation.
That is backwards. A model should predict itself better than it predicts reality. The standard reading is that these models produce a predictable signal that is too weak relative to their own internally generated noise — so the ensemble mean, taken at face value, systematically under-states the forecast anomaly, and has to be scaled up before it can be believed.
The practical consequence for a reader: a European winter outlook showing a mild-looking +0.3 °C ensemble-mean anomaly may be a much stronger statement than it looks, and a site that shows you the raw ensemble mean without saying so is showing you a misleadingly timid map.