Re: APPM Models


Lee Dodge
 

I am at a loss to understand the details of the pressure required for the APPM model, and how some folks are getting that from the local weather report.  The APPM model asks for "pressure" in mbar.  My local weather station reports barometric pressure in inches of mercury (Hg).  So, for today, the barometric pressure 30.52 in. Hg., and using a conversion factor of 33.8639 mbar/in. Hg, I would get an absolute pressure of 1033.5 mbar, which sounds reasonable for a nice clear day.  However, my observatory is at 8565 ft. above sea level, or 2611 m.  Using this barometric pressure at my altitude would be nonsense, as I compute the absolute pressure at my altitude and a temperature of -11 C (today's temp.) to be 725.3 mbar.  The difference between the barometric pressure and the actual absolute pressure at my location is that the barometric pressure is always converted to some sea level equivalent, and regardless of how high you go, the barometric pressure is always around 1013 mbar.  If the model is looking for barometric pressure, then it must be labeled barometric pressure rather than pressure, and if it is really looking for pressure, then how are folks getting that from the local weather report.  Which pressure is it looking for?  

Lee

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