[gradsusr] GFS_0p25 and total precip accum

[Jeff Chabot]

Hi GrADS Users,

I am having trouble with computing precip accum using just GFS_0p25
from NCEP.  The source that I am using is the following:

http://nomads.ncep.noaa.gov:80/dods/gfs_0p25/gfs20210622/gfs_0p25_00z

To compute precip, I'm using:
'define precip = const((apcpsfc/25.4),0,-u)'

I set the following variables:
t=1
t0=0

Then, in the while loop, I am using this equation to subtract 0-6
hours from 0-3 hours (Please note, I only need to do this for GFS):
'define rain = const(precip(t='t') - precip(t='t0'),0,-u)'

This works well for a 3 hour interval of precip (every three hours up
to 10 days).

Next, I am trying to apply a sum to it to get total accumulated precip totals:
'define accum = sum(rain,t=1,t='t')'

For other models like NAM, I use the following since I don't need the
define rain:
'define accum = sum(precip,t=1,t='t')'

I then do the counter and then end my loop:

t = t+1
t0 = t0+1
endwhile

I have tried modifying the define accum equation with no luck.  If I
use precip in the equation, then I get ridiculous precip totals of 24
inches for 1/2 of the country in 10 days.  If I use rain, then I'm not
getting total precipitation, instead I'm getting an interval.

Any suggestions would be greatly appreciated.  I suspect that I have
an error in my equation. the correct accum equation.

Sincerely,

Jeff