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How wxdeck works

wxdeck shows what the radar sees, what seven forecast models expect, and how far they disagree. This page says where each number comes from, how fresh it is, and what it cannot tell you.

The radar

  • NOAA's national radar mosaic (MRMS). The National Weather Service's radars, with others in and near the US, merged into one picture of the lower 48 states after NOAA's own quality control. A new frame arrives about every 2 minutes.
  • Rain and snow in different colors. MRMS also classifies what is falling, and the map uses it to draw snow apart from rain.
  • The next 60 minutes. The last 20 minutes of radar give each area of rain or snow a direction and speed, and the map carries it forward. It does not make storms grow or weaken, which is why it stops at 60 minutes. After that, the map shows a weather model's forecast radar (HRRR), out to 24 hours.
  • The public radar page shows observed radar only.

Seven forecast models, and the range

Forecast models often disagree, and one number hides that. wxdeck runs seven and shows the spread:

  • NBM: NOAA's National Blend of Models. Reaches about 11 days ahead.
  • HRRR: NOAA's High-Resolution Rapid Refresh. Reaches about 2 days ahead.
  • GFS: NOAA's Global Forecast System. Reaches about 16 days ahead.
  • ECMWF: the European Centre (ECMWF), its main model. Reaches about 15 days ahead.
  • ICON: Germany's weather service (DWD). Reaches about 8 days ahead.
  • AIFS: the European Centre (ECMWF), its machine-learning model. Reaches about 10 days ahead.
  • GEM: Environment and Climate Change Canada. Reaches about 10 days ahead.
  • The line is the average of every model that has a value for that hour, each weighted the same.
  • The band runs from the lowest model to the highest. A wide band means a less certain forecast. With fewer than 2 models left, as happens far ahead where the shorter models stop, no band is drawn rather than a narrow one that would look certain.
  • Model data reaches wxdeck through Open-Meteo, a service that carries each model's own output.

Snow forecasts

  • 499 US ski areas, each forecast at mid-mountain, halfway between its base and summit, and at the base and summit too.
  • The headline number is NBM at mid-mountain for the next 7 days. Beside it, the range of the models that look the whole week ahead.
  • Snow, not just water. Models forecast the water that falls. How much snow that makes depends on the temperatures through the air above the mountain, so wxdeck works it out from them rather than using one fixed ratio for every storm.
  • The snowfall range on the Snow map uses HRRR for the first hours, then NBM's 6-hour totals, out to 10 days.

What “observed” means

  • Snowfall analysis. NOAA's National Operational Hydrologic Remote Sensing Center (NOHRSC) publishes24-hour snowfall analyses on a 0.04° grid, about 4 km across. It is an estimate for that area, which can take in both base and summit, not a measurement on the mountain. Analyses are revised for 5 days, so recent days can change.
  • Snow stations. USDA NRCS SNOTEL stations report snow depth and water hourly. wxdeck shows the change in depth over 24 hours, and calls it that: new snow settles, so the depth rises by less than what fell.

How wxdeck scores itself

  • For each saved place, the forecast is recorded when it is made, for 1, 3, 6, 12, 24, 48 and 72 hours ahead. When that time comes, it is compared with the nearest National Weather Service station's report: temperature, dew point, wind speed, gusts and precipitation.
  • The errors are on the Accuracy page, for signed-in accounts. Only saved places are scored, so the figures describe those places, not the whole country.

Sources

NOAA and the National Weather Service, ECMWF, DWD, Environment and Climate Change Canada, USDA NRCS, OpenSkiData, OpenFreeMap and OpenStreetMap. Every source, with its license and credit line, is on the credits page.

wxdeck is not an official source of weather warnings, and it is not affiliated with or endorsed by NOAA or the National Weather Service. For warnings, use weather.gov.