Start with temperature and dew point at ground level, apply standard lapse
rate to both until the expected temperature and dew point are the same or
within about 2degrees Celsius of each other..

That would be the "expected cloud base" if clouds were to form.
Depth of clouds or vertical development and resulting rain depend on other
criteria, such as instability in the atmosphere, upslope winds, amount of
moisture in the air, there may be enough for cloud development but not for
rain.

BT

"William_F" wrote in message
...
I'm not a pilot, but I've got a question pertaining to aviation
forecasts. I'm a mountain climber who has recently discovered
aviation forecasts that could be very useful in determining cloud base
heights. The idea being that alot of times I'll see a forecast that
calls for rain yet I find out on my climb that I'm easily above the
clouds for great climbing weather. My question has to do with
interpreting cloud base forecasts. For instance, at
http://usairnet.com/cgi-bin/launch/c...nge +Location,
I note that on Saturday at 11:00 am they are calling for a cloud base
of 3000-6500'. I'm assuming (maybe I'm way off, but that's why I'm
asking) that this means if I was climbing a mountain at 10,000', I'd
likely be above the clouds. Yet at 11:00 am on Friday at
http://usairnet.com/cgi-bin/launch/c...nge +Location,
I note a forecast for clear skies and a cloud base of 12,000' to
"unlimited." I'm not sure what this means, does this mean that even
though it is supposed to be sunny, I may encouter clouds above
12,000'?

Can someone set me straight on what this data is supposed to mean?