How a forecast is made

The analysis draws on the surface, upper-air, marine and radar stations of the observing network, together with satellite radiance and scatterometer wind received through exchange with the regional centres. Surface reports arrive at ten-minute intervals, radiosondes twice daily from Lindoma, Solvena and Ferrista, and radar volume scans every five minutes from the four sites.

Quality control runs in three passes: a range check against physical limits, a consistency check against neighbouring stations and against the previous analysis, and a manual pass by the duty forecaster for reports the automatic passes flagged. Rejected observations are retained in the archive with the reason for rejection recorded, since a rejection is itself a datum about the station.

Boundary conditions come from a global model obtained through exchange, and the cooperative runs no global model of its own. Inside those boundaries three models run at increasing resolution over decreasing domains.

Five horizons are issued. The nowcast gives the position and motion of what already exists. The short range gives values with times attached. The medium range gives probabilities. The monthly and seasonal outlooks give the direction in which the period is likely to depart from the normals, with no daily detail of any kind.

Every issued forecast is compared with what afterwards occurred, and the scores are published on the same schedule as the forecasts themselves. Temperature is verified by mean absolute error against station observation, rainfall occurrence by the equitable threat score, and the ensemble by its Brier score and by the reliability of its stated probabilities.

Where the cooperative states a 30 per cent chance of rainfall above 10 mm, rainfall above 10 mm should occur within 30 per cent of the occasions that statement is made. The reliability diagrams for the last five years are published with the raw counts behind them.

Forecasts reach the public through the public information system, through the short code operated by the telephony federation, and through any client that reads the published feed. The feed is the same one the cooperative uses internally, in the same format, with no reduced public version. The National Railways Federation takes the wind, snow and rainfall fields directly, since speed restrictions on the coastal and upland lines are set from them.

Warnings for wind, rainfall, snow, ice, heat, cold and coastal surge use the four-colour scheme and travel on the same channel as the hazard warnings described under REP-KJS, REP-LEW and REP-FEW. A meteorological warning gives lead times measured in hours and admits of human review before issue, which distinguishes it from the automatic systems.

The model configurations, the assimilation settings, the quality-control thresholds and the verification code are published in the repositories listed under specifications. A user with the archived observations may reproduce any past analysis and any past forecast exactly, and the archive is held for that purpose.