This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.
>From: "David J. Knight" <address@hidden> >Organization: . >Keywords: 200001061655.JAA27619 >Hi, > There seems to be a problem in decoding many South American >metar observations using dchrly in gempak. > >Specifically it does not seem to be decoding the altimeter >setting when given in Hpa. > >For example, an observation like: >SBSN 061230Z 25002KT 9999 FEW016 SCT100 28/24 Q1010= >produces a missing value for alti in the surface file. As I >understand it the Q group should be the altimeter setting in Hpa. > >The apparently relevant code in: >gempak5.4/src/bridge/metar/parse_metar.c >is: >if( Mptr->A_altstng ) > *alti = (float)Mptr->inches_altstng; >else > { > if( Mptr->Q_altstng ) > *alti = (float)Mptr->hectoPasc_altstng * 1013.25 / 29.921; > } >Which appears to suggest it should be working properly. (i.e. >it looks like it converts the Q group to alti in inches of mercury) > >Suggestions - help ? > >Thanks >David > >David Knight >Department of Earth and Atmospheric Sciences Tel: (518)-442-4204 >SUNYA ES-228 Fax: (518)-442-4494 >Albany, NY 12222 Email: address@hidden > Dave, I fixed this in a message to Robert Mullenax at: http://www.unidata.ucar.edu/glimpse/gempak/3160 the conversion should be: *alti = (float)Mptr->hectoPasc_altstng * 29.921 / 1013.25; eg, flip the conversion factors. Recompile the bridge/metar directroy to update bridge.a, then recompile and link $GEMPAKHOME/src/programs/dc/dchrly Steve Chiswell