OVERCONVECTION

The promise of a fine, sunny day is sometimes spoiled because cumulus cloud builds and spread out into an almost unbroken sheet of stratocumulus by late morning - which then refuses to break up for the rest of the day. For this to occur, there must be a marked inversion within 100 to 300 hPa of the surface, which must be intense enough to stop convective currents 'breaking - through' the inversion even at maximum temperature; the convective condensation level (CCL) must be at least 60 hPa below the inversion level, and the layer between CCL and inversion must have a reasonably high relative humidity. For some rather obscure reason, this phenomenon has come to be called 'overconvection' (at least in the UK)- possibly because convective cumulus 'spills-over' to cover the sky?