Atmospheric models of fog, clouds and rain are described. These models are typical for mid-latitude temperate regions of the globe. A computer code for incorporating the models into a new efficient computer algorithm of the AFGL HITRAN series named FASCOD1 has been completed. The computer models presented allow calculation of atmospheric transmission or attenuation for millimeter and submillimeter waves (1-34 cm-1 or 1-1000 GHz). Four (4) fog models, eight (8) cloud types and rainfall rates from 1-150 mm hr available. All models consider hydrometeors as having temperatures between 0°C and 40°C and permit arbitrary input of atmospheric parameters and geometry (slant range).