[gradsusr] GFS_0p25 and total precip accum
Jeff Duda
jeffduda319 at gmail.com
Thu Jun 24 00:10:04 EDT 2021
Oh yeah, I almost forgot...the default units of apcpsfc are kg/m^2
(equivalent to mm). If you want values in inches, you need to divide the
final value by 25.4. That should really shave down your final values.
Jeff
On Wed, Jun 23, 2021 at 2:11 PM Bill Reilly <bill_reilly at compuserve.com>
wrote:
> 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
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> > >> 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
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> >
> >
> >
> > --
> > Jeff Duda, Research Scientist
> > University of Colorado Boulder
> > Cooperative Institute for Research in Environmental Sciences
> > NOAA/OAR/ESRL/Global Systems Laboratory
> > Boulder, CO
> >
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>
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--
Jeff Duda, Research Scientist
University of Colorado Boulder
Cooperative Institute for Research in Environmental Sciences
NOAA/OAR/ESRL/Global Systems Laboratory
Boulder, CO
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