On May 16, 1:11*pm, MCC wrote:
Is there a good reason why isobars on a surface pressure chart are spaced
at 4 mb? I would have thought 5 mb spacing would have made more sense.
TIA
--
MCC

5 mb is too wide but is used by GFS maybe because it corresponds
very closely to the 4 dam interval in the 500-mb charts and thickness
charts.
In summer, particularly, a smaller interval than 4 mb would be
useful because of the weaker pressure fields. Also, in a
mesoanalysis, a smaller interval is needed, even 1 mb.
The interval of 4 mb has a long history, even going back to the
days when isobars were labelled in inches of mercury. It's about
right.

Tudor Hughes, Warlingham, Surrey.