Tornadovideos.net chasers managed to intercept some great supercell structures in
July 26, 2015 at 7:24 pm #93579
Numerous recent model runs (GFS up to 12Z on Sun 26th) have shown the potential for a powerful cold-front, reaching the Western Cape during Thurs 30th and Fri 31st. Repeated GFS runs have ‘flip-flopped’ between extreme scenarios (heavy snow or no snow), but are finally starting to converge on a moderate intensity front, with very cold conditions. Edit: A deep surface low (970hPa) will pass far to the south of Cape Town.
The latest model run shows widespread light to moderate snow (below 1500m), though this scenario is likely to continue to ‘wobble’ somewhat over the next 2-3 days. The cold air is likely to extend quite far into the interior, but limited moisture in circulation may mean only a light dusting of snow in places. I will post further updates closer to the time.
Edit: The GFS ensemble has converged fairly well, but still shows some uncertainty in the position of the cold-core cupper trough (500hPa isolines) in this ‘spaghetti’ chart at 12Z on Thurs 30th:
This morning’s NCEP GFS animations give a good overview of likely developments:
Attachments:July 30, 2015 at 10:00 am #93596
Lots of flooding on the roads this morning.
Totals has not updated yet, but i’m sure it will be interesting. But it should be available here at some point today.
http://www.weathersa.co.za/media/data/climate/nr_daily_rai.pdfJuly 30, 2015 at 11:50 am #93597
The ‘first’ cold-front passed over during the night, with heavy rain during the early hours of this morning (Thurs 30th). The current situation can be seen on the EUMetsat Airmass animation and SAWS ship synoptic chart:
Quite strong winds were experienced yesterday (Wed 29th), as a surface low intensified, producing tightly spaced isobars. Several trees were reported to have fallen, blocking roads in some parts of Cape Town.
The SAWS reports significant rainfall in places around the Cape Metropole during the 24 hours to 8am. Highest include Kirstenbosch 49mm, Jonkershoek 47mm, Strand 39mm, Wellington 34mm, Molteno Reservoir (CBD) 33mm, Bellville 29mm, Paarl 27mm, etc.
The cold-core upper-trough associated with the front is lagging somewhat, so that the freezing-level has not yet fallen below 1800m. As a result, the only places that have received snow so far have been the extreme highest peaks in the SW-Cape.
The freezing-level is likely fall gradually during today (Thurs 30th), reaching 1500m over the SW-Cape by midday. However, follwing passage of the front, there is very little moisture in circulation, and only traces of snow are likely at low elevations.
The cold air is likely to move far over the southern interior of SA by tomorrow morning. Scattered moisture is likely to produce snow over parts of the Eastern Cape and southern Drakensberg early tomorrow morning (Fri 31st). It will clear rapidly from the west by the weekend.July 31, 2015 at 8:58 am #93599
At first light this morning (06Z on Fri 31st) the EUMetsat visible (false-colour) image shows widespread (light) snow over parts of the Eastern Cape and southern Drakensberg. The area covered closely matches the model predictions, with the freezing-level as low as 1500m in places.
Edit: Several mountain passes in the area are reportedly closed this morning.
Edit #2: This morning’s Terra Modis overpass (Fri 31st) gives a nice view of the fresh snow over the Drakensberg, as well as several parts of the Eastern Cape.
Attachments:July 31, 2015 at 9:48 am #93602
Just spotted some snow on Stellenbosch mountain. I have a lovely office 😛 Dwarsberg @ 1214m is also currently (31Jul’15 09:45) at 0.1 C. With its temp log recoding a minimum of -1C. So I believe the freezing level probably went down to 1100m overnight. Should have some snow on Table Mountain too then.
Might also be worth checking river levels after this event.
Moderator: I was also watching the temperature at the Dwarsberg site. However, surface (2m) temperatures can be influenced by radiative cooling (clear skies), and are not the same as the freezing-level in the bulk atmosphere. There is no evidence that the freezing-level was below 1400m last night, though flurries of snow may have fallen as low as 1300m (never on Table Mt).August 19, 2015 at 8:12 am #93606
It has been a very quiet and dry month for South-Western Cape so far this month and with rainy season drawing to a close, Cape Town is facing possible water restrictions in the coming summer season, if we do not receive significant rains in the next few weeks. No significant rains is anticipated in the next ten days, according to long range forecast and below-average rainfall is also forecast for September, October and November.
According to some models, West Coast trough is expected to form and migrate southwards towards Cape Town and tropical moisture is likely to be in circulation and isolated to scattered showers and thunder-showers is likely to affect Northern Cape and Western Cape including Cape Town on Saturday, 22 August 2015.
You must be logged in to reply to this topic.