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[GEMPAK #VLS-573998]: Adding new parameters in surface SHIP files

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  • Subject: [GEMPAK #VLS-573998]: Adding new parameters in surface SHIP files
  • Date: Tue, 17 Apr 2007 10:58:18 -0600
> Steve,
> 
> So for example, if a station reports SLP=550 with no altimeter
> settings, GEMPAK would decode it as 955.0mb instead of 1055.0mb?
> 
> Kwan

Actually, in a METAR, the valid range without altimeter is 980 to 1049
as seen in $GEMPAK/source/bridge/mt/mtslp.f:
C
C*      Check for the altimeter setting in millibars or inches.
C*      If neither exists, then the mean sea level pressure can have
C*      the range of 980-1049 mb.
C*
C*      If the altimeter exists, get the value in millibars.
C


With altimeter, it will start at 1000 + coded slp, and then iterate downward
using altimeter with a minimum value of 800mb. So, the only way to decode a
PMSL of 1054 in a metar report would be to have the altimeter.

Steve Chiswell
Unidata User Support


> 
> ----- Original Message -----
> From: Unidata GEMPAK Support <address@hidden>
> Date: Monday, April 16, 2007 6:26 pm
> Subject: [GEMPAK #VLS-573998]: Adding new parameters in surface SHIP
> files
> 
> > > Hi Steve,
> > >
> > > Didn't realize that you replied my last email until now.
> > >
> > > I have several questions/comments since my last email.
> > >
> > > 1. When I tested the script of analyzing the North America
> > isobars for
> > > a day in March, I noticed the objective analysis made a strange low
> > > near the center of a 1054mb high in northern Canada.  After
> checking
> > > the data there, I found some stations had pressures in the 950mb
> > range> while others are correctly decoded as 1050s.  I concluded
> > that GEMPAK
> > > set 950 as the critical pressure for determining if the METAR
> > pressure> was in the 900's or 1000's.  GEMPAK also used the
> > altimeter settings
> > > to help this determination.  So stations that reported altimeter
> > were> decoded correctly.  (Is that right?)
> >
> >
> > That is the way that the decoder is supposed to work using the
> > altimeter to
> > figure out the PMSL value. If you see otherwise, let me know.
> 
> 


Ticket Details
===================
Ticket ID: VLS-573998
Department: Support GEMPAK
Priority: High
Status: Closed