Weather Question: forecasting clouds

I've been wondering about this for a while now, and am sure someone here
will know...

How can I find/figure out what the forecast cloud bases will be 3 or 4 days
out? I've looked on ADDS, AOPA's weather, NOAA.gov, etc but not found
anything.

In other words, if I'm going flying in a few days, And I go to weather.com
and see 'mostly cloudy' in the forecast, how do I know if that's "2000'
better-file-an-ifr-flight-plan Cloudy" or "10,000' VFR-is-no-problem"
cloudy?

I've tried looking at forecast temperatures and dewpoints, and using lapse
rate calculate cloud bases, but that hasn't worked out.

Are there any sites which give this info? or other info I could use to
figure this out?

TIA for your help

-Jonathan