The snow coming thread was getting a bit long, plus a bit confusing for those just reading it for the first time since Octobers dates got messed up, so seemed like a good time to start a new thread....

The snow coming thread is here.

From TWO: 18/11 to 24/11

Quote:
During the middle part of the week there is a significant risk of a major area of low pressure crossing southern or central parts of the UK, bringing heavy rain to southern areas, and heavy snow to northern parts. As this clears all areas will be left in a cold and showery air stream with the possibility of further snow

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The mild spell maybe short lived and not quite so mild.

You can still see snow on the CG webcam, although that will all go, and so so far it just hasn't got too horrendeously mild yet.

By the weekend things cool down with temps on saturday a more seasonal 7 in the highlands, cool enough for snow at the summits.

Then things really start to cool down...

Just out of interest can I ask you guys how do you predict a long-term forecast?

So far it seems as if Weather Outlook's forecast that I posted a little while ago has proved pretty good. They predicted a little cold snap (Friday-Saturday) and then for it to warm up a bit after that. Just hope the rest of their forecasts are correct! I'm amazed there is still a fairly complete (if this cover) at the top. It was 6c at the carpark on Sunday, so it couldn't have gotten much warmer (if at all) than that. Say that, it seems it's gonna get a fair bit warmer from the Beeb forecasts before it does get cooler again. Just hope the 1993-4 model continues as suggested it might.

Well it's looking like a pretty series low pressure is going to smack into some part of the UK Thursday/Friday, on THursday summit temps look like getting down to around freezing so possibly wintry precipitation, then going back up on Friday to a few °c above freezing.

As the low moves south east, during Saturday cooler air will again feed in, with summit temps dropping back below freezing on the basis of this mornings forecast. Some snow likely on the higher slopes, but again going mild on Monday as a warm sector pushes over, but going below freezing on the higher slopes again by Tuesday.

In summary still uncertain as to where the lows will track exactly, but at present they look like giving some high level snow and freeze thaw cycling from the weekend into next week, some hopeful signs for the trend for mid to later part of next week, but as ever, to early to say, need to keep watching the forecasts.

PS Its bound to snow late next week, CairnGorm Mountian closes on the 17th!

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From this mornings model output things are looking fairly promising for a potential dump on the mountains as we go through the weekend cooling down, and then into next week. From the 0z run you could be looking at 10-20cm of snow for the higher slopes of CairnGorm by middle of next week, and more like 30-40 for the top of Aonach Mor. A slight drop in temps from the model would bring the snowline down very usefully, a slight rise from those values would lift it almost above the summit, but if the temperature is right and that depression does indeed get stuck of the Western Highlands, a good chance of significant hill snow on the higher peaks, esp the west!

With the possibility of some thaw/freeze cycling in the middle part of the week, and more snow later, promising signs, and they've been there for days now, so fingers crossed!

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Alan,

Which reports do you refer to and could you provide a link.

Cheers,
JY

A range of NWP computer model output. Visit www.theweatheroutlook.com and go to community -> forums -> weather and you'll be able to find links to various sites showing such data.

A useful one for temperature indication is the UK 850hpa Temperature forecast. This is based on single runs of the GFS (Global Forecasting System) a computer NWP model. The key is not taking a single run from a single model as gospel, you need to consider trends in the model output, how much has things changed since the last output?

This morning's 06z GFS run has chucked a wobbly and if it is right will give summit temps around +7°c on Sunday, where as 6hrs earlier it was like 0! Totally at odds with other forecasts. Forecasters use ensemble forcasts, made up of various runs of the model, this works by inputing slightly altered data input values into the model. This gives an idea to the expected accuracy and relibility of the computer forecast, if all the individual forecasts are a close match, you can be fairly confident that this is what will happen, if they are all over the place, then you can't be.

The reason for this ensable forecasting is, that we can't know the weather at every point in the atmosphere, we have to extrapolate between actual weather stations. This introduces errors into the initial starting data, the ensemble forecasts give an indication as to how significant these 'errors' could be.

Ensemble forecast for Aberdeen

The graph in the link above shows the ensemble elements for the 850hpa temperature for Aberdeen.

The 850hpa temperature is the air temperature of the atmoshpere at the point where air pressure is 850mb, this is aprox. around 5000ft. Given that the average lapse rate for temperature is 1°c per 1000ft, adding 2°c to the 850hpa temperature gives an indicaiton of possible summit (4000ft) temperatures.

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Not to divert the subject (or to make anyone jelous of another country), but the resorts of Lake Louise and Banff in Canada have seen near-record snowfalls. Over the past 3 days, 80cms of snow has fallen over the resorts which has pushed the snowbase at both resorts over 100cm. And they have more forecast for today before temps are due to drop to the region of -20c with clear sunny skies. Why couldn't my ancestors have been kicked out of Scotland to the Canadian colony during the Highland clearances ;-)

From [url=http://www.theweatheroutlook.com/othskiing.asp]The Weather Outlook, visit their site for the full snow outlook:

Quote:
Skiing forecast headline:

In Scotland conditions are likely to be colder than recently with the possibility of heavy snowfall at times. The main risk is there will be milder sectors crossing at times and these will melt some of the snowcover. Despite this, it is possible that during the first half of December there MAY be some good early season snow.

Issued 22/11/03

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The current model runs are very mixed up, but it does not look to good for next weekend, just about tropical again, could go either way. If there is not some reasonable snow fall this week, it's worrying in that we are in danger of having a predominently mild November, which would swing us back to the autumn 2002 pattern.

There seemes to be a battle between potential very cold scenarios and very mild scenarios, and the next month upto Christimas could be critical, providing an indication of which way it will go. Unless it is cold for a couple of weeks now, and then cold and snowy over Christmas, the indications are not good. I've said several times that this winter will be one extreme or the other, unless the next month delivers, I think the odds are starting to tip away from the good season to the poor season end of the scale. Fingers crossed that the tide will turn back again.

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Still looking good on snow-forecast though, 39cm of snow still forecast for Nevis range this week and it's looking snowing on the nevis web-cam! Do you have any more info on the weekend weather? The forecast on TWO is still looking quite cold for the weekend. Still hope..................

the nevis web-cam isn't there anymore though, is it?

there's another site, check it out at:

[www.visit-fortwilliam.co.uk]

Well there has been a few light showers pass through Fort William today and they have left a dusting on top of the snow from Friday which took a bit of a battering in the mild weather yesterday. The gullies on Ben Nevis appear to have filled a bit though.

Its pretty cold today so hopefully the snow that is left is freezing and forming the beginnings of a base, fingers crossed !

snow-forecast has predicted high temps from wed night but the met office are predicting a cold weekend now, who do we believe? Alan, could you spread some light on the matter?