With (most of) the custom GFS models updating, and the outcome of this event coming closer, it is time to post a few charts. Freezing-level charts and likely snow can be seen on the site snow-forecast.com: www.snow-forecast.com/maps/dynamic/southafrica
The NCEP ensemble charts should also be available soon.
This custom GFS chart (based on the 00Z run on Fri 3rd) shows the temperature at the 500 hPa level (roughly 5000m elevation) at 00Z on Tues 7th (96 hours ahead). The extreme disturbance from normal conditions can be seen, with temperatures about 15C below the seasonal average (-30C vs -15C).
This disturbance is likely to have two effects, the first obviously being very cold conditions near the surface, with widespread snow. The second is instability, due to cold air moving over (relatively) warm and moist air near the surface. This could lead to rapid intensification of the surface low (although the position of this low is not clear yet).
Possible outcomes include heavy rain showers, and the development of a cutoff-low along the southern Cape coast (not KZN) on Tues 7th, although it is not possible to make detailed predictions at this stage (4-5 days in advance).
Compiled by Gordon Richardson - StormchasingSA
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