The 5-Day Quantitative Precipitation Forecast (QPF)
products are created by adding HPC's 6-hour QPFs for Days 1-3 (a total of 12 6-hour periods) to
a 48-hour forecast for Days 4-5 prepared by our medium-range forecasters. This forecast is
issued twice per day, once at 12Z and again at 23Z.
Both forecasts are valid from the beginning of Day 1 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 120-hour period from 12Z September 2, 2004 through 12Z September 7, 2004.
The forecast prepared at 23Z September 2, 2004 would be valid from 00Z September 3, 2004 through 00Z September 8, 2004.
www.weather.gov 
Rainfall