Rain and storm for Cpt pt 2

satanboy said:
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🚨⚠️ CAPE ON HIGH ALERT: TWO STRONG COLD FRONTS INCOMING ⚠️🚨 After severe weather caused WIDESPREAD DAMAGE and DISRUPTION across the Southern Cape, attention now turns to the SOUTH-WESTERN CAPE. Two...
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Are there any threads on the forum about the wild weather the Karoo/Garden route has been experiencing?
 
Today (Sat 9th) is the calm before the storm, sunny with a few clouds, but a growing NW wind.

The SAWS ship synoptic chart only shows the first cold front, but a very deep low behind it, and unobstructed flow from the SW bringing cold air from the sub-Antartic (unlike the recent cutoff-low).
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I know you said Gordon that the models are a bit optimistic in non mountain areas, but I dont think i would want to be in franschoek or too close to the berg river (those val-de-vie guys)
Up to 300mm over 3 days coming in the mountains with very heavy falls Monday into Tuesday.
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Rocco1 said:
I know you said Gordon that the models are a bit optimistic in non mountain areas, but I dont think i would want to be in franschoek or too close to the berg river (those val-de-vie guys)
Up to 300mm over 3 days coming in the mountains with very heavy falls Monday into Tuesday.
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I'm keeping an open mind, particularly since I'm in the middle of a PC upgrade/repair, and can't look at my usual model details. Remember that CT has had hundreds of years of winter weather, and before the advent of computer models, there was no detailed way of charting the expected outcomes. In reality the SAEON Dwarsberg mountain catchment station records an annual average of 3000mm, so this one event is not as exceptional as the recent cutoff-low along the Garden Route.

I will note that this is a prolonged event. The actual hourly forecast on yr.no shows rates of 10-12mm/hr for 24 hours consecutively. This sounds like a huge amount of rain (and 300mm is a lot), but steep river valleys will be able to carry most of this water away. The effects downstream could be worse though. In low-lying areas like the Cape Flats rainfall is likely to be close to 100mm, and waterlogging will occur.

P.S. The Berg River dam is only 50% full (very early season), and will provide a partial buffer to the main channel flows. After this event the levels are likely to have risen 10% or more.
 
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A general observation from my side of the pond.

In the past few hours there's been a downward trend in air pressure (current 1003) and humidity (current 43%) and temperature rising in .0 increments.

Curious to know what awaits us within the next 12hours.
 
I live between Stellenbosch and Franschhoek (Banhoek valley), going to be fun :D We have had these type of events before over the past 10 years,; never really have long standing water, just a lot of runoff into the Dwarsrivier on the way to the Bergrivier.
 
The latest 3 day chart from snow-forecast.com captures the majority of this event, up to 8am on Tues 12th. Note that while there will be a lot of snow during Sun 10th, slightly warmer rain on Mon 11th will melt most of it. Do not expect good snow chasing conditions, except for a small gap late on Sunday afternoon, and possibly early on Monday morning:
southafricasnownext3days[20260512_0600].jpg
 
Rocco1 said:
I know you said Gordon that the models are a bit optimistic in non mountain areas, but I dont think i would want to be in franschoek or too close to the berg river (those val-de-vie guys)
Up to 300mm over 3 days coming in the mountains with very heavy falls Monday into Tuesday.
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Followup post. I had a bit of time to look at some model runs on my phone (not ideal). See: https://www.cpc.ncep.noaa.gov/products/international/cpci/data/00/fcsts_safrica.shtml

The front on Sun 10th is a normal winter event. Mon 11th is a different animal altogether. A rapidly deepening low (called explosive cyclogenesis) will develop just south of CT, along with an inflow of moist sub-tropical air (an atmosperic river) will bring prolonged orographic rain.
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Gordon_R said:
Followup post. I had a bit of time to look at some model runs on my phone (not ideal). See: https://www.cpc.ncep.noaa.gov/products/international/cpci/data/00/fcsts_safrica.shtml

The front on Sun 10th is a normal winter event. Mon 11th is a different animal altogether. A rapidly deepening low (called explosive cyclogenesis) will develop just south of CT, along with an inflow of moist sub-tropical air (an atmosperic river) will bring prolonged orographic rain.
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Yes, tonight still looks alright. Will be the last night on the stoep until Wednesday. Monday morning looks pretty hairy for Kommetjie.
 
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