Understanding Weather – not predicting – 04 April 2013

What happened?
While the southern hemisphere has experienced astonishing downpours, in Namibia we had good reason to query our prospects.
The desirable weather patterns were on the way though. A sharp cold front extending northward from an intense vortex close the Antarctic shore was advancing east toward the Cape. The upper air trough was just as significant. The significance lay in an obvious clearance of the already weakening middle level anticyclonic core which had taken root across the South-Atlantic for the past dozen or so weeks. Within a couple of days, the southerly airflow was replaced by a developing flow from the northwest bringing with it some moist air throughout its deepening stream of air. Initially, the air-stream was both narrow and limited in its depth. However, the increasing impetus of the circulation provoked by the advancing cold front trough and the tightening isobars proved itself. Within 12 hours the positive development of both convective cumulus cloud and the increasing middle level clouds showing turbulence were visible and active. Shower activity appeared more widespread.
The vortex core was also active. Responding to the thrust of the mobile anticyclone advancing along the 40S range, the frontal push sagged along its northern reach and developed its own closed core vortex: a cut-off low was forming.