[gradsusr] NAM and APCPSFC data

Mark Sponsler msponsler at comcast.net
Fri Oct 14 13:26:18 EDT 2016


Hi Jeff,
Thanks for the info. 

Yeah, I use the first time step which of course has no precip data in it. So the cycle would start with t = 2.

Just to confirm, for either the 1 hr NAM or the 3 hr NAM, I simply should use the below logic and all should be good?

In other words, the 1 hr NAM accumulates in 3 time step sequential bundles (timesteps 2,3,4 refresh then 5,6,7, refresh etc) and the 3 hr NAM accumulates the same. 

Display Time = 2Time 3 = Time 3 - Time 2Display Time 3Time 4 = Time 4 - Time 3Display Time 4

Display Time = 5
Time 6 = Time 6 - Time 5
Display Time 6
Time 7 = Time 7 - Time 6
Display Time 7

etc...

Thanks,Mark


----- Original Message -----From: Jeff Duda <jeffduda319 at gmail.com>To: GrADS Users Forum <gradsusr at gradsusr.org>Sent: Fri, 14 Oct 2016 16:59:14 -0000 (UTC)Subject: Re: [gradsusr] NAM and APCPSFC data



Mark,
Why do you not think it works the way you described in (1)? That's the way I've always used it, and I've never had a problem. The particular t-index value you use in grads depends on how you setup the control file. If you didn't start the time index at forecast hour 0, then there will be a phase difference between what you think and what actually works.


Jeff Duda

On Fri, Oct 14, 2016 at 10:55 AM, Mark Sponsler <msponsler at comcast.net> wrote:

Hi,I'm trying to display variable 'apcpsfc' from the 3 hr and 1 hr NAM.  The resulting images appear to pulsate/accumulate precip every few images then reset only to accumulate again.

I've seen the threads in the archive on this issue with HD GFS data, but I'm trying to understand 2 things:

1) What is the accumulation period for NAM 1 hr and 3 hr data.  I was thinking it was every 3 time steps (i.e. excluding time step 1 / 00 hr), it is 2, 3, 4 then reset and start accumulating again for the next 3 time steps 5, 6 and 7).  But that doesnt seem to be the case. 

2) What does it mean to 'normalize' the data? Westly did something in wgrib2 for HD GFS data to normalize it and I was wondering if that was also applicable to NAM data.  What is done to mathmatically to get the data to be valid for just a single timestep?.  Can I write something in GRDADS to perform the normalization rather than having to use WGRIB2. 

Assuming the accumulation theory is correct (that apcpsfc accumulates every three time steps), I've been trying to write code to remove the accumulation by:

Display Time = 2Time 3 = Time 3 - Time 2Display Time 3Time 4 = Time 4 - Time 3Display Time 4

But it doesnt work. 

Any help would be appreciated.

Thanks,Mark        


Thanks,Mark
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-- 


Jeff DudaPost-doctoral research associateUniversity of Oklahoma School of Meteorology




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