Hi, I suppose you mean GFS model forecast. A note: This model is run by NOAA/NCEP, we can't influence how the the model is run anyhow... what we do is read the cloud cover from the output files and display it here, we do not modify the model data anyhow in this case - we show the numbers exactly as they are in the model output. I noticed the GFS model shows less cloud cover since the GFS upgrade in 2010, but don't know why... this is rather question for NOAA.
Just wanted to ask how it's possible in the forecast for today for Czech Republic- Prague that it should rain in the evening while cloud covers are zero...