I'm still running occasional side-by-side tests of the advforecast2.php script (old-4.03 v.s. new-5.05) to see how the NWS current forecast from forecast.weather.gov compares to the API-driven forecast at forecast-v3.weather.gov.
Usually, they are mostly identical. Today's rain probability and amounts seem to differ quite a bit (higher probability and values for the still 'beta' API forecast).
Guess they have more work to do on the API version (or maybe it is the 'improved' version that makes better forecasts.. don't know)