grib file wind arrows

Answer
GRIB files use wind barbs or arrows to represent wind speed and direction. Here's how to interpret wind arrows in GRIB files: Wind barbs indicate both wind speed and direction. The line or shaft of the barb points in the direction the wind is blowing from. The wind speed is shown by the number of "flags" or "pennants" on the end of the shaft:
  • Short pennant = 5 knots
  • Long pennant = 10 knots
  • Triangle = 50 knots
So a wind barb with a shaft pointing northwest and two long pennants indicates a wind of 20 knots blowing from the northwest. Some key points about wind arrows in GRIB files:
  • The arrows represent wind vectors, showing both speed and direction at that grid point.
  • GRIB data uses the U and V wind components to define the wind vector, which viewers interpolate to display as arrows.
  • Interpolation between grid points can sometimes lead to inaccurate wind speeds near weather fronts if not implemented correctly.
  • It's best to check the actual forecast wind speed values rather than relying solely on the arrow lengths.
In summary, wind barbs/arrows in GRIB files provide a convenient way to visualize wind flow across the forecast area, but you should verify wind speeds against the data values for highest accuracy.
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