Hey everyone, man its good to be back on this website. Dont know when last ive posted or commented on the website!

Ive been following post from both xmesox & gordonr during the winter months even though winter was a bit dull this year in Cape Town(dull for me at least compare to past 3 years).

Summer rainfall season is around the corner & I wonder what xmesox will be up to when he storm chases again this season. Summer is more my kind of weather with strong winds, Hot temperatures & of course Thunderstorms!

Ive notice something on the GFS Modules for next week between 6-8 September 2010, looks like some interesting weather heading this way although its to soon to tell. The SAWS are predicting a strong SE Wind for Tuesday into Wednesday with a 60% chance of rain. hmm? makes me wonder.

i noticed SAWS has changed there report to thundershowers for next week Tuesday and Wednesday for cape town, i hope this materializes
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haha, looks like something might just happen. lets wait and see!

Is it going to be a cut-off low system? Hope something exciting happens. this winter's storms have been rather mild. yeah bring on the summer thunderstorms

Hi guys. I alerted Xmesox to this one by e-mail yesterday, but the GFS models have been very inconsistent, so I didn't start a thread (yet).

This mornings's 00Z GFS run (Fri 3rd) was quite encouraging, but the 12Z GFS run is much less so.

Edit: The SAWS web forecast is always (up to 18 hours) behind the GFS, so the page that Clock3r posted is already out of date...

In any event it looks rather messy, with a lot of moisture, but very marginal instability (with some elements of a cutoff low).

I can post some charts if you want, but they will surely change in the next few days.

I always look at the GFS ensemble, not just the specific forecasts. The GFS ensemble has 14 model runs (once per day), that show the variety of possible outcomes for a particular parameter.

For the 500hPa level, this morning's GFS ensemble (Fri 3rd) shows huge uncertainty (> 500km) in the position of the upper trough as at 12Z on Tues 7th.

For a 108 hour (4.5 day) forecast this indicates low confidence in the specified scenario.

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Another way of looking at the GFS ensemble, is to check the possibility of rainfall exceeding a certain threshold.

In the case of the 1mm (per 6hrs) chart, for 12Z on Tues 7 this is less than 50%, which is very low confidence IMO.

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One more way of looking at the GFS ensemble (there are about 14 parameters!) is to look at the areas where each ensemble member indicates the possibility of 50mm rainfall in 24 hours, which would be a significant event.

For 12Z on Tues 7th only a few ensemble members indicate this possibility, most of the ensemble members show the rain far offshore, or none at all.

I hope this of of some use in understanding how models work

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Some Nice mammatus clouds over the northern suburbs this evening. Quite unexpected! unfortunately the photo I took on my cellphone was not great

This morning's GFS run (00Z on Sat 4th) shows a broad area of moist sub-tropical air moving down from Namibia on Wed 8th. This is 108 hours (4.5 days) ahead, so there is still considerable uncertainty in the models.

The most likely scenario is a patch of moist, marginally unstable air moving close to Cape Town. The surface temperature is too low for major convection, so it will problably be rather cloudy and damp and messy...