 brian
brian
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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brian, Niederschlag is a great word. Thanks for the chart.
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brian
brian
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Frosty the Snowman, almost as good as Doppelsesselbahn 
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You need to Login to know who's really who.
You need to Login to know who's really who.
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brian, there's good agreement for the temps there until 12th. Precipitation's a bit more hit and miss (though 6th/7th looks good with temps slightly higher). I haven't looked at the chart, but the noticeable sawtooth in temps suggests transition to HP?
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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Can someone please explain what all the squigley lines mean?
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You'll need to Register first of course.
You'll need to Register first of course.
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Looking at the chart, a low pressure system moves in bringing a pool of cold air, before moving of NE bringing some northerlies on it's western edge with high pressure follosing in over the western UK. If that came off there would be snow showers at least in the mountains, and the UK will feel noticeably cooler, too.
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brian
brian
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johnboy, squiggly lines across the middle are the temperature in the atmosphere where the pressure is 850mb (surface is ~1000mb, so 850 is usually round about 1500m up but it varies depending on whether you're in high or low pressure situation). The thick red line is the 30 year average.
Squiggly lines at the bottom are precipitation (in mm of rain). Very roughly 1mm of rain corresponds to 1cm of level snow (ie. no drifting effects) but due to the effects of mountains you can usually bump the numbers up or down a bit depending on the aspect of the mountain and the direction the snow's arriving from.
The reason there are multiple lines in different colours is because this is an ensemble forecast, explained nicely by carled here:
http://snowheads.com/ski-forum/viewtopic.php?p=297411&highlight=ensemble+gfs#297411
The thick white lines are the means for temp and precip of all the ensemble runs.
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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brian, beat you! 
Incidentally, there's some reasonable agreement from ECMWF & UKMO (up as far as you can see their output), too.
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brian
brian
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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| Quote: |
| anyway I think you're better at it |
brian, we'll agree to disagree. 
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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brian & skanky, no matter who's the 'best' it's good to have both of you speculate (should that be forecast?) what the snow gods have in store for us. Hopefully we will have a cold and dynamic season for you to get your teeth stuck into 
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You know it makes sense.
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II, the thick red line in the middle is the 30-year average temperature for those dates. The thin, coloured lines represent different forecasts. The white line is the average of the forecasts. The conclusion is that, on average, the forecasts predict that it's going to be a bit colder than usual after 4th October.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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II, the upper lines are plotted against the figures on the left. These are the temperatures (in *C) at a height of roughly 1500m. The lower lines precipitation and plotted against the right hand axis (these are plotted as mms of rainfall, even though it may fall as snow - but then nearly all rainfall starts off as snow).
Incidentally this chart is not necessarily unique to GFS (it's just another model), but it is, AFAIA, the only global model where all of the output is freely available to the public. There is a model run by the University of Basel that's a bit more experimental where all/most output is available. I'll post a link if I get a chance.
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Poster: A snowHead
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Ignoring such things as temperature inversions, is there a typical decrease in temperature for a given increase in altitude? I vaguely remember the term "adiabatic" from the meteorological module I did many moons ago. For example, if the GFS forecast was for 5ºC at 850mb (say 1500m) what would be the forecast temperature for 3000m?
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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rob@rar.org.uk, I think 2 deg C per 300m is the rule of thumb.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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laundryman, thanks.
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brian
brian
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rob@rar.org.uk, for dry air, 1 degree C per 100m. This is reduced when the air is moist by condensation releasing the latent heat of vapourisation, so I think in the middle of say, a warm front, it could be as little as 1 degree C per 300m.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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brian, thanks. A further question: how dry is dry? Is the 1ºC per 100m for a theoretical mass of air, or would this rate of cooling apply to a typical cloud-less day in the mountains?
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brian
brian
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rob@rar.org.uk, unsaturated, ie. no condensation happening. So yes, this would apply to the cloudless day.
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brian, Thanks, this is like Meteorology 101 this morning
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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II, Like me, you need the women's guide to weather forecasts.
1) Will it snow. Yes/very likely/not very likely/no.
2) A guess at how much.
3) Will it be cold enough to have to wear an extra fleece and/or long johns.
Thank you.
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maggi,
1) Forget the first and last options. These are all that's possible:
Will it snow? It is snowing / Very Likely / Not Very Likely / It isn't at the moment
(you could add a middle "Likely" if you wanted)
3) That depends on how cold it has to be to need to wear them.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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maggi, I'm not really clever. 
Looks to have warmed up from the 9th and is hovering around average temps after that. However, I've heard (ahem, read) more than one person say that GFS tends towards average in uncertain situations so it's just adding to the uncertainty.
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FAQ
You're really clever; you study all those charts and data and that's all you can tell us? 
