I like to do my cross country planning a few hours before the flight (in a C172). But in order to get the pressure alt., which the cruise performance charts are made for, you need to have the altimeter setting which is given in the METAR on the hour.

is there such a thing as forecast altimeter settings?

NO, but a guy can make a pretty good inference by looking at a pressure chart and seeing what’s happening out there.

If you’re getting that detailed with regards to pressure altitudes that is.

You can measure it off the GFA. To convert hPa to in.Hg, divide by 1013.15 and multiply by 29.92.

The engine won’t burn accurately enough anyway so don’t worry about it.

photofly wrote: ↑Wed Feb 07, 2018 8:56 pm You can measure it off the GFA. To convert hPa to in.Hg, divide by 1013.15 and multiply by 29.92.

This is a great tip! thx guys.