The Environmental Conditions Behind the Formation of Small (subLCL) Clouds

SubLCL clouds are defined here as clouds that form below the estimated lifting condensation level (LCL), on days that are predicted to be cloud-free. On more than 50% of those days we observed clouds. Measurements of thermodynamic and sky conditions are used here together with numerical simulations to study subLCL clouds’ formation. It was previously demonstrated that humidified parcels in mid-boundary layer (BL) are likely to be the driving mechanism. We found the height of the LCL above the BL top and the RH near the BL top to be good predictors of the appearance of these clouds. In addition, the average change in RH in the rising parcels that form them was found to have a specific constant value (4.4 (Formula presented.) 0.2[%] per 100 m of elevation). This value enables the prediction of subLCL clouds’ formation on days that rising parcels can reach saturation while moving up in the BL.