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Model Inconsistencies Leave Snow Potential Up In The Air

Model Inconsistencies Leave Snow Potential Up In The Air

Firstly, I’d like to state the discussion of this upcoming weather events poses a larger than normal degree of uncertainty and that it should be noted by all readers that due to the timeframe of the events discussed herein, it’s still very possible for there to be significant changes to the outlook.

Update #3 – 24 June 2015 (09:00): There is always a challenge in forecasting, and it’s definitely wise to mention the potential for changes in outlook when forecasting more than 72 hours into the future. This article has turned into a great example of just how easily forecast models change their outlooks, especially in cases where the forecast hinges on a single feature, in this case a low pressure.

The latest 00z GFS run shows a scenario far different to that shown yesterday, with good amounts of snowfall (in excess of 20cm accumulation) possible for Lesotho, as well as the north eastern parts of the Eastern Cape this weekend. Yesterday the forecast was showing absolutely no snow for the eastern parts due to a lack of moisture and change of position of the low, today however the models are back to showing moisture, in fact they are now showing a large band of moisture moving eastwards from the Northern Cape, which will reach Lesotho and the northern parts of the Eastern Cape on Saturday. Freezing levels look to drop to around the 2500 meter mark in places — but a lot will still depend on the timing of freezing levels and moisture, variables that can still change dramatically.

Apart from the snow potential, there also exists the possibility for heavy rains over the Karoo late on Friday and into Saturday morning as the cut-off low moves eastward (At least that’s what the latest models are indicating).

We’ll continue to monitor what the models suggest tomorrow morning, however things should start to line up within the next 48 hours, as we head into a more reasonable outlook timeframe.

In the more immediate future, the cold front has already arrived in the Cape bringing with it some thundershowers, heavy rains and strong winds. Snowfalls are likely tonight and into tomorrow morning over the mountains of the SW Cape, with the potential for some light snowfalls around the 1500 meter mark. There is also a marginal possibility for light snow in Sutherland with freezing levels around the 1800 meter mark.

lesotho-snow

Image from Snow-Forecast

Update #2 – 23 June 2015 (09:00): Well things have certainly taken a turn for the worst for those looking to chase snow up country. On the weekend, as can be seen below – the long range models were showing a scenario that was impossible not to talk about, with huge snow totals possible for Lesotho and the Eastern Cape. However, the trend has since been one of less and less snow, with some of the new model runs suggesting the possibility of absolutely no snow for both of the provinces. The reason for the change in outlook was one that was discussed in the original post below. The low pressure which was forecast to develop, on which the snow forecast for the provinces hinged, is now no longer set to develop as early as before. It is also set to develop far to the west of the original forecast position. Because of this, it means that there will be insufficient moisture present, though it is also partially due to the less than favourable freezing levels now forecast.

However things continue to look good for the Western Cape, as we expect snowfalls to occur from early Wednesday morning, through until Thursday morning. Initial snowfalls may be quite good, with over 10cm possible – though this will only be at higher altitudes. Early on Thursday morning, the freezing level are forecast to drop to around the 1500 meter mark, which will be more favourable for lower level snow, however moisture becomes a concern at this point, and any snowfall at lower altitudes is likely to be light.

Update #1 – 22 June 2015 (09:00): The latest GFS model run from 00z indicates what was an all to likely probability, the latest forecast has changed dramatically between yesterday and the forecast for snow for Lesotho and the Eastern Cape into this coming weekend has diminished. The latest charts seem to show freezing levels being less favourable, as well as a lot less moisture being present. This is all due to how they are forecasting the low that is set to develop later into the week. As we expressed in the original publication of this discussion, there’s still a bit variable at play, and it’s almost impossible to put out an accurate forecast at this stage. However, it can be noted that there’s good certainty about light snowfalls for the Western Cape on the higher mountain ranges on Tuesday night and into Wednesday morning.

We’ll continue to watch how the forecasts evolve regarding the low pressure system, and for all we know things could be looking optimistic again in the next run.

Original Outlook – Published 20:00 on 21 June 2015: The first system to bring the possibility of snow is a cold front which is set to push into the Western Cape late on Tuesday afternoon and bring with it colder air and the chance for light snowfalls over the higher mountains of the Western Cape, freezing levels at this point don’t look too promising, so it’s likely that any snow would be quite isolated and not good for snow chasing. Freezing levels are set to drop later into Wednesday night and Thursday early morning, however the problem then will lie with the lack of moisture, with the cold front already having past.

western-cape-snow-forecast-late-june

Image from Snow-Forecast

The really interesting parts of the model runs over the past 2 or so days has however have been focused more to the north east of the country. Snow may already begin to fall on the high grounds of the north eastern parts of the Eastern Cape as early as Thursday, but the bulk of the current forecast suggests snow will be at its heaviest into the weekend. The forecast models at the moment are extremely aggressive on the amount of snow that is forecast to accumulate in both the Eastern Cape and Lesotho. The reasons for the very optimistic forecast by the models is the development of a sharp trough (with potential to form into a cut-off low) which evolves through Friday.

Heavy snow shown over Lesotho, with rates up to 20cm per 6 hours. Image from Snow-Forecast

Heavy snow shown over Lesotho, with rates up to 20cm per 6 hours.
Image from Snow-Forecast

low-snow-june-2015

A lot depends on this low pressure development and is the reason why we emphasized the uncertainty involved in this event. Freezing levels are looking promising, but with the forecast still a week away – things can and are more than likely going to change dramatically before the event arrives. The development of the low pressure system in the northern parts will dictate how much moisture both Lesotho and the Eastern Cape see. If the low does develop as forecast, it will bring plenty of moisture to areas of low freezing levels and with it, snowfalls could potentially accumulate in excess of 40cm in under 24 hours, which would be massive. On the other end of course, is the potential that the low doesn’t develop as currently shown by the models and that a lack of moisture decreases the chances for snowfall.

Updates will be posting here in this article during the course of the next week, as the models evolve… However, if ever there were a snow event to keep a close eye on, this is it.

This weather event is being discussed in the forums.

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