How SKC Weather Produces Its Forecast Graphics

SKC Weather turns numerical weather data into interactive maps and point graphics. The source forecast and SKC’s derived display are different layers of the process: a familiar color scale does not change the underlying model’s resolution or uncertainty.

Source fields and members

The ensemble pipelines use NOAA GEFS and ECMWF Open Data for EPS and AIFS ENS. They read numerical fields and member forecasts from GRIB data using Python tools and GRIB readers. RRFS and MRMS are separate forecast and observation products. SKC Weather does not generate the global forecast models themselves.

Calculations happen before display

• Threshold maps: precipitation is accumulated over the product’s period for each member, then members meeting the threshold are counted.
• QPF summaries: the inspected GEFS family calculates ensemble-mean and P90 amounts for 6-, 12- and 24-hour periods.
• Temperature maps: member fields support the offered summary products, with displayed temperature units identified on the map.
• Anomalies: reference climatological fields are used for standardized comparisons. The 500-mb example is explained in the anomaly guide.
• Spaghetti plots: selected contours preserve information about individual members rather than showing only an average.

From arrays to maps

The inspected rendering code uses Python numerical and plotting libraries, including NumPy, Matplotlib and Rasterio. It handles coordinates, map projection, color scales and overlays to produce image layers. The browser then combines those layers with an interactive basemap and the controls for product, time, playback and opacity.

Zoom changes the viewing scale, not the resolution of the original forecast. Reprojection and display interpolation also do not add observations. Use the product legend for physical units; pixel colors are a visualization, not a new measurement.

Availability follows publication

Product catalogs and frame metadata describe which outputs the viewer can load and their run and valid times. Different products or forecast hours can become available at different times. A new initialization is not a guarantee that every requested image is ready. History selection and current-run selection should always be checked before comparing frames.

Point products and quality limits

Plumes process member guidance near the selected location into time-series graphics. They are generated separately from the global map images; a point result and a map may need their run labels checked before comparison. Local terrain, unresolved features, upstream gaps and shared model errors remain limitations.

SKC Weather is operated by retired National Weather Service meteorologist Charles Ross. Its ensemble displays build on work by Rich Grumm and others. Sources and credits are collected on About SKC Weather. These are independently processed displays, not official NOAA or ECMWF endorsements.