About the Day 4-5 QPF

The Day 4-5 Quantitative Precipitation Forecast (QPF) products are prepared by our medium-range forecasters twice per day, once at 12Z and again around 23Z.

Both forecasts are valid from the beginning of Day 4 through the end of Day 5, with the later issuance offset by 12 hours. For example, a forecast prepared at 12Z September 2, 2004 would be valid for the 48 hour period from 12Z September 5, 2004 through 12Z September 7, 2004. The forecast prepared at 23Z September 2, 2004 would be valid from 00Z September 6, 2004 through 00Z September 8, 2004.