How the NPVU interpolates the Forecast and Observation Grids

Method Definitions:

Area Preservation Technique

The Area Preservation Technique is an interpolation method that was developed by NCEP/EMC to interpolate QPF from native NWP model grids to output grids, while preserving the aerial amounts of QPF. This technique is similar to calculating an integral in calculus. Where the one grid is divided into sub-grids and then used to ensure that the output grid is coarser or finer than the original grid. It is most beneficial when the ratio between original to output or output to original is less than 4 to 1. If the output is much finer than the original then linear interpolation is better or if the output is much coarser than the original than spatial averaging is better. These two methods work just as well but without as much computation.

Change coverage area

The Eta is received on the 32km grid but it is for a much larger geographical area. This area is then "cut" down to the grid size needed to cover just the CONUS RFC areas.

Linear Interpolation

Come back later to learn more

No Conversion Needed

This is the exact grid the NPVU verifies on, so no change is needed

Spatial Average

The spatial averaging technique is a simple average of all of the original grid points with in the area of the output grid.