Hi, the cloud base calculated by the formula mentioned (Henning's formula) holds for convective clouds only, or for a cloud base in a well mixed boundary layer. I know it as SPREAD * 125 = Base in Meters. As you can imagine, layer clouds may form by different processes which are beyond the reach of a simple formula like this.
The depiction of the freezing level on a map is a bit more complicated. I am working on this subject using a combination of RAOB and DA. The charts I am producing can be seen on my HP
http://www.wetteruwe.de. It is in German, made for Europe thunderstorms, and still 'heavily under construction'. I am awaiting some improvements of DA for a better accuracy, and the number of charts will increase. The charts appear - if everything runs smoothly - starting 45 min after the radiosonde hours, updates are made till t+2 hours.
Uwe