Understanding Weather – not predicting – 28 June 2013
Weather’s diversity gave another sample of its extensive repertoire for the spectators here in Namibia. In a multi-dimensional atmosphere, the full range was on offer.
On the surface, the ability to experience 3 bands of temperature remained present for much of this last week. Intermittent cold in the southern parts, adjacent warmer days for the central parts, while the north could have daytime temperatures close to the 30oC mark.
The upper air saw another cirrus band appear, spread, depart and reform across consecutive days from differing sources.
High level cloud patterns appeared by mid-week from a source west of the Congo estuary, flowing southeast eventually merging with an upper vortex extension which passed south of the Cape.
The disturbance forming this cloud source was not easily identifiable yet there was ample uplift to condense into a visible cloud pattern in an unusual area for this time of year.
While the winter weather season should remain dominant for another eight weeks or so, so will the frequently described ability for “cut-off” vortex formation in either upper or sea-level patterns remain a likely possibility.
Such developments are enhanced by the persistent recurrence of major anticyclonic cores with high pressure ridges extending to the antarctic, tapping polar air and sweeping some of this frigid, unstable, airmass across the southern ocean to the African continent. Despite this airflow crossing a very cold ocean, it picks up some moisture bringing it across Namibia, and visible as high altitude streaks. Once over the warmer parts of the landmass, solar heat provides warmth and convection, making the clouds more prominent.
What happens after this depends on the prevailing synoptics of the hour and day in question. Considerable rains are not unknown!
One way or another, anticyclonic control persists over the eastern sub-continent ensuring a north wind control. Conditions on the ground remain unchanged, basically warmer by day with chilly nights. Sunday sees a noticeable drop in temperature with an ensuing colder Monday but by Tuesday, mild days return. By Wednesday it has formed a trough extending high into the upper air. This system moves rapidly to the east taking with it any prospects of rain for the South, however meagre.
The country at large is in typical winter gear but there are no immediate indications of frost. The very mild winter continues.