About SKC Weather
SKC Weather brings ensemble forecasts, high-resolution model guidance and radar into interactive tools for exploring weather patterns. Our viewers help you compare forecast possibilities, follow changes over time and examine guidance for a location. SKC Weather is an independent weather-information site, not an official warning service.
Who operates SKC Weather
Retired National Weather Service meteorologist Charles Ross owns and operates SKC Weather. The ensemble tools build on work by Rich Grumm and others using GRADs over more than 20 years. SKC Weather provides independently processed displays and tools for meteorologists and advanced weather enthusiasts.
Explore the learning guides for worked explanations of the displays.
The forecast systems
- GEFS is NOAA’s Global Ensemble Forecast System. It runs multiple forecasts with different starting conditions and model perturbations to explore possible global weather outcomes.
- ECMWF EPS is the ensemble prediction system from the European Centre for Medium-Range Weather Forecasts, also called IFS ENS. Its physics-based forecasts provide another view of the range of plausible outcomes.
- AIFS ENS is ECMWF’s Artificial Intelligence Forecasting System ensemble. It uses a data-driven model to generate multiple possible forecasts. Comparing it with physics-based ensembles can help identify agreement and differences; it is not a guarantee of greater accuracy.
Reading probabilities and guidance
A threshold probability summarizes how many ensemble members meet a specified condition. For example, if 12 of 30 available members exceed a rainfall threshold, the member fraction is 40%. This describes that model sample, location and accumulation period—not certainty, rainfall duration or the fraction of your day that will be wet. Check the product label, units and time window before comparing maps.
The ensemble mean summarizes the members but can smooth out local extremes. A wider spread suggests more disagreement; a narrow spread does not rule out shared model errors. Plumes show how the range changes with forecast time. Compare successive runs and multiple systems, rather than treating one member or a distant forecast hour as a precise prediction.
Updates and timestamps
Upstream GEFS and ECMWF ensemble forecasts are produced in scheduled UTC cycles. GEFS uses 00, 06, 12 and 18 UTC cycles; ECMWF’s current IFS and AIFS products also have scheduled cycles, with availability and forecast length varying by product. SKC Weather publishes supported guidance as it is received and processed, so a new model start time is not a promise of immediate availability here.
RRFS guidance updates as new forecast data become available; MRMS radar updates as new observations are processed. Check the displayed initialization time, valid time and latest available frame. A forecast hour is measured from the model’s start time; UTC (also shown as Z) is not necessarily your local time. Downloads, processing or upstream outages can delay updates.
Sources and attribution
Primary weather sources are NOAA/NCEP GEFS, NOAA/NCEP RRFS guidance, NOAA’s Multi-Radar Multi-Sensor (MRMS) system, and ECMWF Open Data for EPS and AIFS ENS. SKC Weather processes source data into its own displays and derived guidance; these are not official NOAA or ECMWF forecasts or endorsements.
ECMWF products shown here are based on ECMWF data, adapted for SKC Weather displays. ECMWF Open Data are available under CC BY 4.0 and ECMWF’s published terms. Basemap credits remain on the maps; contributors include Esri and OpenStreetMap where shown.
Forecast limitations
Models approximate the atmosphere. Local terrain, storm timing, precipitation type and intensity can differ substantially from guidance, especially farther into the future. Radar is an estimate and may contain gaps or artifacts. Data and service availability are not guaranteed. Use National Weather Service forecasts and warnings in the United States, or your local official weather service elsewhere, for safety decisions. This site is not a substitute for emergency alerts or an aviation weather briefing.