After quite a few days of Moderate Risk tornado issues
April 9, 2015 at 8:17 am #93032
Temperatures in the western half of South Africa have been rising steadily since last weekend’s cold-front, and a surface trough has developed along the West Coast. During today (Thurs 9th) surface temperatures are likely to peak (> 30C), and tropical moisture will move down from Namibia, producing thunderstorms over parts of the Northern Cape this afternoon.
There is already some scattered altocumulus near Cape Town, but the main area of activity is still far to the north, as seen on the EUMetSat Airmass animation: http://oiswww.eumetsat.org/IPPS/html/MSG/RGB/AIRMASS/SOUTHERNAFRICA/
Numerous model runs and charts show the band of moisture and upper instability passing directly over CT overnight into Fri 10th. This will produce scattered showers over a wide area, though it is difficult to predict the amount of rainfall, and whether or not there will be any thunder.
The latest SAWS aviation TAF (terminal forecast) for CT airport shows activity between 00Z and 06Z tomorrow morning (Fri 10th).
TAF FACT 090400Z 0906/1012 20005KT CAVOK BECMG 0922/0924 34010KT
FM100000 34010KT 9999 SCT050 PROB30 TEMPO 1000/1006 TS FEW050CB
The SAWS Aerosport thunderstorm chart for tomorrow (2pm on Fri 10th) shows activity over the southern Cape coast, after the trough has passed to the east of CT during the night:
Attachments:April 9, 2015 at 9:12 am #93046
Bryn De KocksKeymaster
It’s about damn time!
Seems like forever since the last thunderstorms down here. Looks like another case of early morning madness though. Not sure if I’ll be going to sleep tonight, but I will be charging my camera batteries.
The altocumulus this morning are already showing nice signs of instability in the atmosphere, wouldn’t be surprised if we end up with some CB by this afternoon given the surface heating that’s going to occur.April 9, 2015 at 9:29 am #93047
While surface heating near Cape Town will be good today (Thurs 9th), the amount of moisture in circulation is insufficient for development of proper CBs anywhere in the Western Cape, at least until after sunset.
The situation overnight will be the opposite, with lots of mid-level moisture, but minimal surface heating (marginal values of LI and CAPE). This is likely to produce dense altocumulus, with some embedded TQs. Dawn tomorrow (Fri 10th) may see some lingering activity over CT.
The NCEP GFS animations give an idea of the likely flows of moisture, and the scattered patches of precipitation:
http://www.cpc.ncep.noaa.gov/products/african_desk/cpc_intl/africa/mslp.htmlApril 9, 2015 at 3:56 pm #93052
Things have been rather slow, but very warm out here in Kraaifontein (work)
some activity has started to show up on the satellite and some clouds are visible NE (from where i am)
Attachments:April 10, 2015 at 8:28 am #93057
Development of this trough has been tantalisingly slow, though by this morning (Fri 10th) we finally have some activity around Cape Town! A dense layer of altocumulus is directly overhead (8am), with some signs of convection, but rather weak precipitation (raindrops rather than showers).
The satellite images indicate very patchy distribution of clouds, and the current ‘shower’ may be about the best we are going to get in CT. There should be a few more bands of moisture during the morning, before the trough starts to move inland. A fresh north-westerly wind later today will bring cooler surface temperatures, making further convection unlikely.
The trough is likely to linger over the Western interior of South Africa for at least the next 24 hours. Thundershowers are likely over parts of the Northern Cape during today (Fri 10th), and possibly tomorrow (Sat 11th).
Edit: The SAWS website was offline this morning (Fri 10th), and many of the more detailed Aerosport charts have not updated. The aviation charts confirm the limited prognosis for CT.
Edit: The EUMetsat MPE (satellite/radar) animation shows the peak activity has already passed over Cape Town at 8am, and is likely to diminish intensity during this morning: http://oiswww.eumetsat.org/IPPS/html/MSG/PRODUCTS/MPE/SOUTHERNAFRICA/April 10, 2015 at 4:51 pm #93062
Bryn De KocksKeymaster
Here’s a shot from last night, taken at Sir Lowry’s Pass viewpoint.
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