HYSPLIT Forum: hysplitbbs.arl.noaa.gov

Hi,
I would like to plot 3h total precipitation from forecast date in files hysplit.t00z.gfsf.
Looks like they have every 3rd hour a 6-hour accumulated total precipitation. If I have understood
correctly, the first of such values (0Z, I guess) refers to the rainfall of the last 6 hours, right?
I could subtract each value from the next one but still I would have left in each result the term from
-6Z to -3Z.
I can't think of a way to extract 3-hours resolved total precipitation from such parameter.
Of course I could collect just parameters for 6Z, 12Z, etc and divide by 2 but I feel a
little frustrated to have in some way a higher resolved value without being able to extract it.
Thank you for the help,

Stefano

Yes, in hysplit.t00z.gfsf, the 00z, 06z, 12z, and 18z valid time precipitation values give the amount for the last 6 hours. At valid times 03z, 09z, 15z, and 21z, they give the amount for the last 3 hours. To get the series of 3-hourly precipitation, directly use the values at 03z, 09z, 15z, 21z, and for the other hours subtract the 3-hourly from the next 6-hourly. For example to get the precip from 03z to 06z, take the the 06z value minus the 03z value.

Wow, so while 00z, 06z, 12z, .... are true TPP6, 03z, 09z, 15z, and 21z are actually TPP3?
I haven't found this description anywhere in the GFS and ARL site. Is this an undocumented
feature or could you give me a link to a document where this and the other in depth structures of gfsf
files are presented? I wish to avoid ignoring basic documentation.
Thank you very much for your help and the prompt answer. I appreciate it.
Regards,

Stefano

At http://ready.arl.noaa.gov/READYflddesc.php it says TPP6 is 6-hour accumulated precipitation.

TPP6 means there is a 6-hour accumulating 'bucket'. Imaging a bucket outside collecting rain. At 00z the bucket is empty. At 3 hours, you measure the depth, it is 1 inch. Then at 6 hours you measure again and it is 3 inches, and you empty the bucket to start again for the next 6 hours. That means from hour 0 to 3 it rained 1 inch and from 3 to 6 it rained 2 inches (3-1). Analogously, in the GFS the TPP6 at hour 3 is 1 inch, and at hour 6 it is 3 inches. The precipitation is accumulating with time over the 6-hour period. At hour 3 TPP6=TPP3.

This TPP6 is in the GFS grib files output from NCEP. These are converted to make the HYSPLIT-formatted file.