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20050105: pressure tendency in sflist

Clint,

The pressure tendencies aren't computed by GEMPAK,
rather, they are reported in the METAR observation in
the 5appp group, so they are what are reported
as you will see when you add the TEXT parameter to sfparm.
There is no GEMPAK computational voodoo there...it is all
at the NWS office.

For the 00Z and 3Z LNK observations, the SLP in the remarks are
SLP296 and SLP294 respectively, which yield 1029.6 and 1029.4
millibars (using the altimeter group to determine the leading
"10".

Unfortunately, 1029.6 and 1029.4 are lacking in significant digits
to arrive at the .4 millibar change encoded in the appp group.
I could come up with a case of 1029.65 and 1029.35 which would yield
a pressure change of .3 millibars.   Similarly, I can arrive to
within .1 mb using the SLP and +/-.5 fir the other times. Now, if we 
used station pressure...we have altimeter to hundreds of inches, but would
have some D correction to figure out. So, we just don't have the
full information available in the METAR that the NWS office did,
so it might be worth a check with the NWS to get the logged values
especially if you were trying to trace a gravity wave event.

Steve Chiswell
Unidata User Support


>From: Clint Rowe <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200501051714.j05HEIv2008648

>Chiz,
>I was just looking at some pressure tendencies using sflist and they don't
>seem to be computed correctly.  Maybe I'm missing something, but only one
>(09Z) of the 3-hour tendencies from today's obs at Lincoln seems to be 
>correct.
>
> GEMPAK-SFLIST>l
> SFFILE   = metar
> AREA     = @lnk
> DATTIM   = /00;/03;/06;/09;/12;/15
> SFPARM   = stim;pmsl;ptnd;ptsy;p03c;p03d
> OUTPUT   = t
> IDNTYP   = STID
> GEMPAK-SFLIST>r
> PARM = STIM;PMSL;PTND;PTSY;P03C;P03D                                         
>   
>
>    STN    YYMMDD/HHMM      STIM     PMSL     PTND     PTSY     P03C     P03D
>    LNK    050105/0000   2354.00  1029.60  3024.00  3999.00     2.40  3024.00
>    LNK    050105/0300    254.00  1029.40  5004.00  5999.00    -0.40  5004.00
>    LNK    050105/0600    554.00  1029.50  1002.00  1999.00     0.20  1002.00
>    LNK    050105/0900    854.00  1027.20  6023.00  6999.00    -2.30  6023.00
>    LNK    050105/1200   1154.00  1029.00  1016.00  1999.00     1.60  1016.00
>    LNK    050105/1500   1454.00  1029.20  3001.00  3999.00     0.10  3001.00
>
>
> Parameters requested: SFFILE,AREA,DATTIM,SFPARM,OUTPUT,IDNTYP.
> GEMPAK-SFLIST>
>
>This is version 5.7.3, I haven't upgraded to latest version yet.
>
>Clint
>
>====================================================================
>Clinton M. Rowe
>Associate Professor 
>Meteorology/Climatology Program                  phone:(402)472-1946
>Department of Geosciences                          fax:(402)472-4917
>University of Nebraska-Lincoln                        address@hidden
>
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