[gradsusr] Multiple accumulation periods

Wed Mar 14 09:53:55 EDT 2018

Scott,

For these complicated variable, the g2ctl/alt_g2ctl makes variable
names that are too long for grads.  You can edit the ctl files to
make shorter names but it is easier to use alt_g2ctl and the
-short option.  I am going to focus on alt_g2ctl because it
has the most timing options.

GrADS has only 1 time dimension.  Grib files can have several
time dimensions.  One goal of alt_g2ctl is to map one
of the grib times to a the GrADS time.

ASNOW Total Snowfall [prob]:surface:240-246 hour acc fcst

In the above field, there are 3 possible time variables.

1) start of the model run time (or analysis time).

  alt_g2ctl:  -0  ignore 240-246 hours in the variable name
              -0t "240-246 hour acc" in the variable name

2) start of averaging/accumulation period (240 hours + start of run time)
  alt_g2ctl:  -b   ignore 240-246 hours in the variable name
              -bt  "240-246 hour acc" in the variable name

3)  end of averaging/accumulation period (246 hours + start of run time)

  alt_g2ctl:  -e   ignore 240-246 hours in the variable name
              -et  "240-246 hour acc" in the variable name

So the meaning of the time is controlled by the option to alt_g2ctl.
If you forgot the options to alt_g2ctl, the options used are listed
in the ctl file.

 Wesley

On Tue, Mar 13, 2018 at 4:12 PM, RENTSCHLER, SCOTT A GS-12 USAF ACC 16
WS/WXNM <scott.rentschler.1 at us.af.mil> wrote:

> All -
>
> I'm generating some post-processed information based off an ensemble.  So
> for example, I might be generating the following parameters:
>
> ASNOW Total Snowfall [prob]:surface:240-246 hour acc fcst:prob
> >2:probability forecast
>
> ASNOW Total Snowfall [prob]:surface:240-246 hour acc fcst:prob
> >4:probability forecast
>
> ASNOW Total Snowfall [prob]:surface:234-246 hour acc fcst:prob
> >4:probability forecast
>
> ASNOW Total Snowfall [prob]:surface:234-246 hour acc fcst:prob
> >6:probability forecast
>
> ASNOW Total Snowfall [prob]:surface:222-246 hour acc fcst:prob
> >2:probability forecast
>
> ASNOW Total Snowfall [prob]:surface:222-246 hour acc fcst:prob
> >6:probability forecast
>
> …and I’m writing these fields in GriB2 format.    In this example, I’m
> generating the data off of the GFS ensemble, writing out the information
> every 6 hours, with data valid at that forecast hour.   So the above
> records appear in the 246 hour forecast file.
>
>
>
> Note that we have a couple of fields then that, when using g2ctl, or even
> alt_g2ctl, would have identical variable names as they only differ in the
> accumulation period –
>
> ASNOW Total Snowfall [prob]:surface:240-246 hour acc fcst:prob
> >2:probability forecast
>
> ASNOW Total Snowfall [prob]:surface:222-246 hour acc fcst:prob
> >2:probability forecast
>
>
>
> ASNOW Total Snowfall [prob]:surface:240-246 hour acc fcst:prob
> >4:probability forecast
>
> ASNOW Total Snowfall [prob]:surface:234-246 hour acc fcst:prob
> >4:probability forecast
>
>
>
> ASNOW Total Snowfall [prob]:surface:234-246 hour acc fcst:prob
> >6:probability forecast
>
> ASNOW Total Snowfall [prob]:surface:222-246 hour acc fcst:prob
> >6:probability forecast
>
>
>
> The g2ctl utility outputs the following entries into the control file:
>
> ASNOW2e3GTsfc  0,1,0 a1,2   0,1,29,1 ** surface prob >2 Total Snowfall
> [prob]
>
> ASNOW4e3GTsfc  0,1,0 a1,4   0,1,29,1 ** surface prob >4 Total Snowfall
> [prob]
>
> ASNOW6e3GTsfc  0,1,0 a1,6   0,1,29,1 ** surface prob >6 Total Snowfall
> [prob]
>
>
>
> The alt_gt2ctl:
>
> ASNOWdprob_>2dprobability_forecastsfc 0 0 "ASNOW.prob_>2.probability_forecast:surface"
> * ASNOW.prob_>2.probability_forecast:surface
>
> ASNOWdprob_>4dprobability_forecastsfc 0 0 "ASNOW.prob_>4.probability_forecast:surface"
> * ASNOW.prob_>4.probability_forecast:surface
>
> ASNOWdprob_>6dprobability_forecastsfc 0 0 "ASNOW.prob_>6.probability_forecast:surface"
> * ASNOW.prob_>6.probability_forecast:surface
>
>
>
> …and alt_g2ctl using the “–short” flag:
>
> v1 0 0 "ASNOW.prob_>2.probability_forecast:surface"
>
> v2 0 0 "ASNOW.prob_>4.probability_forecast:surface"
>
> v3 0 0 "ASNOW.prob_>6.probability_forecast:surface"
>
>
>
> My problem is that I’m unsure how to reference the different accumulation
> periods for the given parameters.  If I were to create a template for a 246
> hour forecast period, and within the GrADS command line interface, input
> “set t=42”, and try to display one of the above parameters, how do I know
> which one I’m displaying and how does one switch to a different
> accumulation period?  I’m hoping to avoid creating new files containing
> subsets of the above data, but at the moment I’m not sure how to work
> around it.  Is there a way to give each accumulation period a unique ID or
> an appropriate mechanism for identifying differing accumulation periods for
> a given parameter?
>
>
>
> Thanks!
>
> Scott
>
>
>
>
>
> //Signed//
>
> Scott Rentschler, Meteorologist
>
> Fine Scale / Ensemble Models Team
>
> 557th Weather Wing, 16WS/WXN
>
> DS: 271-3331 Comm: (402) 294-3331
>
>
>
>
>
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>
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