"C Kingsbury" wrote in message
om...

1. I find the 2C/1000' "rule" actually gets the bases right most of
the time when the temperature is much over 45 degrees where I fly in
New England.

The cloud base calculation for convective cloud relies on the difference
between the dry adiabatic lapse rate (the rate at which the temperature of
lifted air falls with height) and the rate at which dewpoint falls with
height. The former is about 3 degC/1000ft at the lower levels, the latter
is about 0.5 degC/1000ft. Thus the difference is 2.5 degC/1000 ft or,
flipped around, the air can rise about 400 ft per 1 degC of spread before it
condenses.

That has little to do with the ISA average lapse rate of 2 degC/1000 ft, but
the value is similar, hence your observation is correct.

Julian Scarfe