Variabili GFS relative alle precipitazioniacpcpsfc | ** surface convective precipitation [kg/m^2] | apcpsfc | ** surface total precipitation [kg/m^2] | cpratsfc | ** surface convective precipitation rate [kg/m^2/s] | pratesfc | ** surface precipitation rate [kg/m^2/s] | pwatclm | ** entire atmosphere (considered as a single layer) precipitable water [kg/m^2] |
Note:1 kg/m2 = 1mm of water (because of the density conversion - 1000 kg of water per meter cubed). The values will be (almost exactly) the same because the density of water is approximately 1000 kg/m3, so the total mass of a 1-mm layer of water covering an area of 1 m2 is 1 kg. GFS total accumulated precip (apcpsfc) includes all forms of precipitation that reaches the surface during the accumulation period. For forecast hours evenly divisible by 6, the accumulation period is from T-6h to T, while for other forecast hours (divisible by 3 but not 6) it is from T-3h to T (Eric L. Altshuler). PRATE is actually the time average precipitation rate over the same periods that are used to accumulate APCP. In other words, PRATE is the average precip from T-6h to T for T=6,12,18,24,... and from T-3h to T for T=3,9,15,21,... The same "peculiarity" in APCP also applies to PRATE. PRATE and APCP are proportional to each other. For T=6,12,18,24... PRATE=APCP/21600 (6h=21600s). For T=3,9,15,21,... PRATE=APCP/10800 (3h=10800s)(Eric L. Altshuler).
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