NDFD Forecast Data

A weather-savvy boater always begins their marine forecast with a review of the large-scale features. This strategy is a sound one because the weather we are concerned about – wind, waves, and thunderstorms – are associated with large-scale features such as highs, lows, and frontal boundaries. There is no better source for surface weather maps than NOAA’s Weather Prediction Center (WPC) (click here).

Surface forecasts from the WPC are available seven days into the future at 12 to 24-hour intervals and display important features such as isobars, surface troughs, lows, highs, cold fronts, warm fronts, and occluded fronts. If your map interpretation skills are rusty, please check out the article I wrote a few years ago (click here).

In addition to surface weather features, WPC surface forecasts also display Weather Type guidance from the National Digital Forecast Database (NDFD) using color shading. The NDFD is a gridded forecast system used by National Weather Service (NWS) offices to coordinate their forecasts across the United States. The legend for NDFD elements shown on the WPC forecasts appears in the lower left corner of the map and includes:

  • NDFD Rain (Chance) – areas shaded in light green indicate a 10% or less chance of rain.
  • NDFD Rain (Likely) – areas shaded in dark green indicate greater than a 10% chance of rain.
  • NDFD Snow (Chance) – areas shaded in light blue indicate a 10% or less change of snow.
  • NDFD Snow (Likely) – areas shaded in dark blue indicate greater than a 10% chance of snow.
  • NDFD Mix (Chance) – areas shaded in light purple indicate a 10% or less chance of a rain/snow mix.
  • NDFD Mix (Likely) – areas shaded in dark purple indicate greater than a 10% chance of a rain/snow mix.
  • NDFD Ice (Chance) –areas shaded in light gold indicate a 10% or less chance of ice.
  • NDFD Ice (Likely) – areas shaded in dark gold indicate greater than a 10% chance of ice.
  • NDFD T-Storm (Chance) (Hatched) – areas outlined in red and annotated with red diagonals (hatching) indicate a 10% or less chance of non-severe thunderstorms.
  • NDFD T-Storm (Likely and/or Severe) – areas shaded in dark red indicate greater than a 10% chance of non-severe thunderstorms, or a chance of severe thunderstorms.

Interpreting the NDFD Weather Type is a straightforward process of comparing the color shading on the map to the legend. The ability to review the large-scale features and the expected weather type at the same time significantly increases the value of the surface forecasts.

NDFD forecasts are also available for a wide variety of additional parameters such as wind speed / direction and wave heights. The interactive viewer is available at https://digital.mdl.nws.noaa.gov/.