[gradsusr] GFS_0p25 and total precip accum
Bill Reilly
bill_reilly at compuserve.com
Wed Jun 23 16:04:38 EDT 2021
I don't know if this helps, but this is how I display 3hr precipitation:
if (tstep="006" | tstep="012" | tstep="018" | tstep="024" | tstep="030"
| tstep="036" | tstep="042" | tstep="048" | tstep="054" | tstep="060" |
tstep="066" | tstep="072" | tstep="084" | tstep="096" | tstep="108" |
tstep="120" | tstep="132" | tstep="144" | tstep="156" | tstep="168" |
tstep="180")
'd (apcp03-apcp03(t-1))*10'
else
'd const(apcp03,0.001,-u)*10'
endif
--
Bill Reilly
(+34) 686-110-748
bill at passageweather.com
www.passageweather.com
On 06/23/2021 20:49, Jeff Duda wrote:
> Then I'd start checking the apcpsfc arrays in your individual files,
> because that might be the culprit.
>
> By the way, your looping syntax is incorrect. In grads, you perform
> modular arithmetic using R = math_fmod(N,D) for remainder R, number N,
> and divisor D. So you would use
> if (R = 0) ...
>
> On Tue, Jun 22, 2021 at 3:19 PM Jeff Chabot <jsc219 at gmail.com
> <mailto:jsc219 at gmail.com>> wrote:
>
> Hi Jeff,
>
> Thanks for the quick response. I removed the const function. I was
> using that part for my precip type equations, but as you said, I
> probably don't need it.
>
> As for what you mentioned, I couldn't get it to work. I am trying to
> show a running total of precip accum every 3 hours even though it
> alternates between 3 and 6 hours precip.
>
> So, I came up with the following based on what you wrote:
>
> if (hh = 0 mod 6)
> 'display sum(apcpsfc/25.4,t=1,t-0,2)'
> else
> 'display sum(apcpsfc/25.4,t=1,t-1,2) + apcpsfc/25.4'
> endif
>
> Where hh = forecast hour.
>
> Unfortunately, it is still resulting in overestimated values such as
> 8-12 inches of total precip in 32 hours when it should be more like
> 3-5 inches and I don't have precip accum until hour 6 (hour 3 I get no
> data).
>
> I am missing something, I just don't know what.
>
> Thanks again,
>
> Jeff Chabot
>
>
> On Tue, Jun 22, 2021 at 11:19 AM Jeff Duda <jeffduda319 at gmail.com
> <mailto:jeffduda319 at gmail.com>> wrote:
> >
> > Jeff,
> > It seems you are overcomplicating this.
> >
> > First, why are you using the const function for your sum? There
> should be no negative values nor any undefined values in the
> apcpsfc field. If there are, then there are problems at the level
> of the data processing upstream of you.
> >
> > Second, my understanding of the precip array in GFS output is
> that it alternates between 3- and 6-hour accumulation. So at 0300,
> 0900, 1500, 2100, apcpsfc contains 3-hour precipitation, whereas
> at 0000, 0600, 1200, and 1800 UTC, apcpsfc contains 6-hour
> precipitation. That means that pairs of adjacent time stamp
> apcpsfc arrays are not independent of each other; the 6-hour
> accumulation field completely contains the 3-hour precipitation
> field. Therefore, if you are looking for run-total precipitation,
> you only need to sum the apcpsfc arrays every other time stamp up
> to the time before the valid time (or the valid time itself, if
> the forecast hour is divisible by 6). The simple function
> math_fmod(t,6) will give you the ability to decide if you are
> computing this for forecast hours divisible only by 3.
> >
> > In essence, your display command really only needs to be
> >
> > * if forecast hour = 0 mod 6
> > 'd sum(apcpsfc,t=1,t-0,2)'
> > * else
> > 'd sum(apcpsfc,t=1,t-1,2) + apcpsfc'
> >
> > ...or something similar to that.
> >
> > Jeff Duda
> >
> > On Tue, Jun 22, 2021 at 8:43 AM Jeff Chabot <jsc219 at gmail.com
> <mailto:jsc219 at gmail.com>> wrote:
> >>
> >> 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
> <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
> >> _______________________________________________
> >> gradsusr mailing list
> >> gradsusr at gradsusr.org <mailto:gradsusr at gradsusr.org>
> >> http://gradsusr.org/mailman/listinfo/gradsusr
> <http://gradsusr.org/mailman/listinfo/gradsusr>
> >
> >
> >
> > --
> > Jeff Duda, Research Scientist
> > University of Colorado Boulder
> > Cooperative Institute for Research in Environmental Sciences
> > NOAA/OAR/ESRL/Global Systems Laboratory
> > Boulder, CO
> > _______________________________________________
> > gradsusr mailing list
> > gradsusr at gradsusr.org <mailto:gradsusr at gradsusr.org>
> > http://gradsusr.org/mailman/listinfo/gradsusr
> <http://gradsusr.org/mailman/listinfo/gradsusr>
>
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org <mailto:gradsusr at gradsusr.org>
> http://gradsusr.org/mailman/listinfo/gradsusr
> <http://gradsusr.org/mailman/listinfo/gradsusr>
>
>
>
> --
> Jeff Duda, Research Scientist
> University of Colorado Boulder
> Cooperative Institute for Research in Environmental Sciences
> NOAA/OAR/ESRL/Global Systems Laboratory
> Boulder, CO
>
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
More information about the gradsusr
mailing list