Understanding Weather – not predicting – 24 May 2013

What happened?
The departure from one pattern to a more favourable one is now an established feature on our synoptic charts for both the surface and throughout the upper air. The reversion to more normal patterns coincided with the approach of a very promising front which was expected to develop into a cut-off vortex and stagnate for a day or two. This system collapsed but gave rise to an equally well-marked pattern which also brought about the collapse of the extensive, dominant upper air anticyclonic presence which had held sway for the past few months.
As this new vortex pattern evolved it began the advection of moist air from the fringes of the tropical air persisting west of the Congo estuary. Because this pattern persisted, this advection also continued, intensifying as its moisture depth increased from a few hundred feet to some 2 or 3 thousand feet. This persistence was rewarded as local convergence lines appeared with comparable thundery cloud patterns identified both by satellite imagery and personal observation across much of Namibia.