 Poster: A snowHead
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Mountains shrouded in cloud as I sit looking out the window in Annemasse. Metro suggesting a few flakes above 2000m are possible this morning.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Teeny bit of new snow here at 2000m in Plagne Centre. Right on the rain/snow line. Brightening up now.
Maybe a bit cooler.
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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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| Weathercam wrote: |
Hells Bells, pam w, so the red sand that appeared on my van, and all the other cars in the valley yesterday must have been there from Feb and must have been there all along since then and only appeared after the rain washed the surface "dirt" off yesterday, and of course what the avalanche bulletin of yesterday was alluding to yesterday was also said Feb deposits  |
I didn't say that, I said there had been some earlier in the season as well.
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GFS seems to be flipping back to the (relatively compared to current weather) cold+snow scenario for Tuesday/Wednesday for Austria on the 00Z and 06Z runs as far as I can tell? Is this supported by ECMWF and ZAMG?
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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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What I still don't understand is why, when there is supposedly no overnight freeze, the pistes are boilerplate in the morning - for hours, in the case of less sun-exposed aspects.
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You'll get to see more forums and be part of the best ski club on the net.
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pam w, there is Pam. We were in Austria a couple of weeks ago and snow forecast was saying that minimum nighttime temperatures were 5 degrees or so.
We woke to a frost every morning.
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pam w, the answer is that both evaporation of liquid water and sublimation of frozen water will also cool the surrounding air as it cools itself. Overnight snow surface freezing won't happen in mild and windy conditions but given calm enough atmospheric conditions, the phase change cooling will overcome the warm air mixing ...
http://www.theweatherprediction.com/habyhints2/524/
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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I actually think this GFS run is quite good - resort level at Ischgl is around 1500 (850hpa) and 90% of the pistes 1800+ so for the time of year I'm actually quite optimistic for my easter in Ischgl.
If resort level temps are around 0c, mountain temps will be -3 and dropping and with a good chance of precipitation I think it should a good week.
I think it's important with these longish range forecasts, to use a number of different resources and to always heir on the side of caution.
I'm not sure what data they use but I use metcheck for UK forecasts and they are forecasting "precipitation" for 17th onwards for Ischgl at resort level. Rain at first changing to snow at resort level as it passes to mid week at easter.
Really looking forward to the week (19th-26th) now the only worry I have now is that this band that are on the Sunday Fettes Brot are going to be rubbish! Regardless of whether me and my mates can understand what they are saying I'm sure we will be enjoying ourselves!
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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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| AthersT wrote: |
| I actually think this GFS run is quite good ! |
Yes, that individual GFS 0Z 'operational' run itself would be fabulous but it is 'pie in the sky' at the moment and the next operational (rolling out now) could be 10 degrees warmer ! I'll ignore every operational run for a few days yet and just be cheered that the mean is getting a lot cooler because there are just as many cold options in weather model la-la land as there are warm ones. 
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moffatross, thanks. I've been trying to get my head round that, with some difficulty. the air starts off warmer than the snow surface, snow will be sublimating/melting and therefore releasing latent heat which will cool the air very near the snow. So far so good. But then at some point that air near the surface will be the same temperature as the snow and that process slows down - how can the air get so much cooler than the snow that it causes the latter to freeze? ( I probably shouldn't have given up physics after O level  )
Anyway, it's good that it happens!
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You know it makes sense.
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AthersT, Metcheck will I imagine be using the GFS operational run (as it's free). So not really very useful as a comparison (as it's the same data). The six month stuff is presumably CFS.
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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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| nozawaonsen wrote: |
| AthersT, Metcheck will I imagine be using the GFS operational run (as it's free). So not really very useful as a comparison (as it's the same data). The six month stuff is presumably CFS. |
I was just looking at their 14 day forecast - I don't look at anything further than that. I'll be keeping my hopes in check for a week - after that I will start to take notice of the forecast then as accuracy increases.
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Poster: A snowHead
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pam w, the bit you are missing is that air masses that are ostensibly warm but dry may have low 'dew points' and can readily accept water vapour. So the process in a dry air mass can allow both snow and air to continue cooling so long as the air continues accepting water vapour. Once the surrounding air mass becomes 'saturated' with water vapour, the surface evaporation/sublimation process stops.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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AthersT, if you see a 14 day forecast on the internet it's very likely that it is derived from the GFS operational run. The US makes all this data free so people tend to use it.
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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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moffatross, ah yes. the air is certainly very dry - a pair of heavy denim jeans dries in no time!
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AthersT, the only thing that GFS run really shows is that it's going to be above freezing at resort level for most of the period out to the 12th. After the outputs of the different runs diverge significantly, so as far as I'm concerned it's anyones guess, outputs from +15 to -8 degC, take your pick.
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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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I thought the main reason snow freezes on seemingly warm nights was due to long wave radiation. Snow just can't wait to radiate away the heat from the day. Needs clear calm nights with dry air. I'm sure a weather expert can give a more correct explanation.
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| waynos wrote: |
| I thought the main reason snow freezes on seemingly warm nights was due to long wave radiation. Snow just can't wait to radiate away the heat from the day. Needs clear calm nights with dry air. I'm sure a weather expert can give a more correct explanation. |
Although there'll obviously be a cooling contribution from radiation away from a surface, I can't help but think about its implications. If radiation was the 'main reason' for snow losing heat, its surface would eventually be able to reach -270 Celsius or thereabouts. There is actually a lot of research going on as to what determines the limiting factor for lowest surface temperatures on the Earth which appears to be around -90C (much warmer than the background temperature of the Cosmos) even in the coldest frost hollows in winter darkness in Antarctica.
And since 'clear calm nights with dry air' are entirely conducive to rapid cooling via evaporation then sublimation (given sub-freezing dew points of the air mass), that seems like the overwhelming mechanism for freezing to me with the air's dew point being the lower limit.
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Am I alone in not wanting any more snow this season?
Fresh snow this time of year is horrible and grabby for at least a couple of days. Never provides much of a top-up either.
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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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snowheads68, yes you are, fresh snow can and often is lovely this time of the year
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moffatross and others, as mentioned before: all this seems to go against the laws of thermodynamics.
If the air is warmer than the snow, the snow should heat up.
I know volatile liquids can evaporate so fast they cool down and can freeze
But we are talking ice crystals here: can the rate of sublimation really account for the freeze?
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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Jonpim, currently, RH's are about 40% across the Alps. If the air temperature around a mile high (850 hPa) is +5C, and its RH is 40%, its DP is around -10C so there's a lot of energy can be taken out of the snow before the air's moisture content rises so high that DP's get above freezing.
P.S. I haven't a clue what the real life parameters are to freeze the snow, i.e. how still the air needs to be, how dry the air needs to be, what the difference needs to be between actual air temperature and its DP etc, but if it's not evaporation then sublimation (and a bit of radiation) that's freezing it, it has to be the pixies. 
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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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I reckon its the pixies 
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The generally mild theme continues, a brief cool down to around average mid week, otherwise above average till at least Good Friday.
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You know it makes sense.
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| waynos wrote: |
| I thought the main reason snow freezes on seemingly warm nights was due to long wave radiation. Snow just can't wait to radiate away the heat from the day. Needs clear calm nights with dry air. I'm sure a weather expert can give a more correct explanation. |
Doesn't need to be calm, just clear so that the long wave radiation isn't reflected back. Indeed wind can cool down the snow further as it removes warm air just above the snow.
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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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Out in Saas Fee this week and it was 14 in the shade, felt more like 20+ in the sunshine at resort level. Still really good up the top but you experience every kind of snow on the way back to resort by midday.
Marginally cooler tomorrow but looks like rain apart from very high ... hoping it will get a bit cooler/stay drier again than the forecast suggests. There was no show for the rain predicted for this afternoon so fingers crossed.
Warm but enjoyable spring conditions so far 
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Poster: A snowHead
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Fairly heavy rain since day break in Les Saisies. Stopped just now and distinctly colder following the rain. Meteo suggesting rain/snow line at 2300m but dropping by afternoon to 2200. Rather hope they are wrong and it will fall further 
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Overcast but dry in Stuben at the moment...
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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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Cooler temperatures in the Alps overnight but the overall picture suggests April will continue above average through to mid month. There's a pretty strong consensus out till 17 April at which point options start to open up a bit (both warm and cool).
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davidof, this talk of "long wave radiation" still seems to suggest heat is moving from cold snow to warm air.
This is contrary to the laws of physics as I understand them.
http://en.wikipedia.org/wiki/Heat_transfer
Quote: "Heat transfer always occurs from a region of high temperature to another region of lower temperature".
Not the other way round.
This article on Snow Hydrology is also intersting.
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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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| Quote: |
Out in Saas Fee this week and it was 14 in the shade, felt more like 20+ in the sunshine at resort level. Still really good up the top but you experience every kind of snow on the way back to resort by midday.
Marginally cooler tomorrow but looks like rain apart from very high ... hoping it will get a bit cooler/stay drier again than the forecast suggests. There was no show for the rain predicted for this afternoon so fingers crossed.
Warm but enjoyable spring conditions so far
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Got back last night from a long weekend just round the corner to you in Zermatt and I agree. The itinerary on the northish facing run down from Stockhorn (3532m) down to Gant (2223m) went from ow, ow, ow over solid bumps at the top down to whoah, whoah, whoah ploughing through slush and avoiding patches of grass at the bottom. Great fun!
As I am now not back out again until late May when only the glacier top will be open I really must stop compulsively reading this thread hoping for good snow news (I bet I don't thought).
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Whilst I'm not about to start getting my head around the nuances of freezing it has been an interesting couple of days, seeing snow refreeze at night when temps have been 30+ in the sunshine.
After the overcast drizzle type conditions of last Thurs and Fri when we did not get 5% of the precipitation forecast, sun did appear along with clearing skies on the Sat, going outside at around 21:00 under a clear sky what chunks of snow are still around in the shade were freezing and temps were 4.5, we're at 1450.
We started (08:00) at a very popular spot at 1710m and people were using crampons on the S facing approach as the snow was so frozen. By the time we came back down at 11:00 this had really softened up.
Same scenario for Sunday night going into Monday, bonkers warm Sun afternoon but again the refreeze. Though we are starting earlier as we know that temps are rising so quickly.
Today is very overcast and drizzle and temps just below double figs with a chill N'ly breeze, so luckily had decided on nothing today because of the forecast, and will be interesting to see how tomorrow works out as meant to be a tour on Thursday with the local Club Alpine.
So like I say nuances of why snow freezes when temps are warm my fuddled old brain has problems (never was any good at physics) understanding, what I do know is that under clear skies and positive temps it will refreeze, the question now is what are the conditions when it will not such as tonight maybe?
Will go out at 22:00 and test some snow, if I can find any lurking
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| Weathercam wrote: |
| question now is what are the conditions when it will not ... |
A/. The rough mechanism was already explained for the freezing i.e. clear mountain air is quite dry and can strip a lot of heat from the snowpack as it absorbs the moisture until some kind of equilibrium is reached. For the lack of freezing, if that equilibrium is reached when the air's dew point is above zero, then no chance.
In real life, if there's low cloud overhead, or it's misty or foggy around you, that air will have a relative humidity of 60%, approaching 100% if you can 'feel' the moisture in the air. At 10C, if the air is 50% RH (could still occur in a clear sky), its dew point is already above freezing so there's no chance of the snow freezing then either.
At the extremes, very dry air (10% RH) at +10C has a dew point of -20C and very moist air (90% RH) has a DP of +8.5C.
Useful calculator here ... http://andrew.rsmas.miami.edu/bmcnoldy/Humidity.html
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Well the rain did indeed come as forecast today. Absolutely chucked it down thw lower half of Saas Fee, extremely low vis and quite windy for a time up the top (several lifts closed for a bit).
That's it for the change though all back on for warm and sunny the rest of the week according to pretty much all forecasts. Much the same everywhere at the moment by the looks of the models?
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There is definitely a breakdown of sorts for the current weather patterns due for around 16th - 20th period.
Within the last few days Ischgl (where I am going on 19th) has been been forecasted to receive 30-50cm of fresh at valley level more up at mid and upper mountain. Then this changed to nothing but rain even up top then back to 30-50cm of fresh again, so at the moment it is very uncertain.
The most certain I think we can be is that the current pattern of mainly warm bluebird days will change and that precipitation is likely to come just whether it is cold and falls as snow or whether it is warm and falls as rain is the big query - fingers crossed it does bring the fresh snow :]
Valley - Level
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