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What factors make snow dry?

post #1 of 32
Thread Starter 

Hi, I'm new to this forum, at least in terms of posting although I like to follow Tony Crocker from time to time inc the best snow website as that man is definately in the know.  


This is a post regarding what constitutes the dryness of snow.  


Although I know the snow is consistently very dry in the Colorado area and significant part of interior North America in general, I was never satisfied with the marketed explanations as to why this was so.  The four main explanations used are altitude, how far from the coast, i.e the higher the dryer, the further from the coast, the drier, the dryer the air the dryer the snow and the colder the air the dryer the snow.  This just didn't sit well with me.  For one thing I am from Europe and mainly ski in the Alps, the Alps have plenty of ski resorts that go just as high as Colorado's highest, the Alps are significantly colder than Colorado (on an altitude comparison), Colorado actually sits in the sub-tropics on the same latitude as Central Portugal, and yet from experience the snow is consistently dryer in Colorado.  I would compare most of the ski areas I have skied in the Alps to have snow conditions more on average closer to somewhere like Whistler.  So with this knowledge that the marketed explanations just didn't add up from my experience I was motivated to do a little research.  


I looked into what makes snow dry?   What I found was snow isn't really dry it’s perceived to be based on the water content of the snow and the water content is derived from the shape of the water crystals that form the snow.  I found that light and fluffy snow is made up of branchy frozen water crystals whereas wetter heavier snow has less and even potentially no branching at all.  So I asked, what factors influence how branchy the crystals are and to my surprise I found the greater the humidity the greater the branching and that the crystal believed to be responsible for super dry snow such as Champagne Powder is largely made up of Stellar Dendrite water crystals which are particularly branchy and refined and only form either very close to freezing (in the cloud - no good as will most likely melt before landing or shortly after) or at or very very close to -15celcius (in the cloud) in high humidity (in the air below); the higher the humidity the drier the snow.  Then I Iearnt that the belief of; the colder it is the dryer the snow, isn't true either because humidity just cannot remain high much after -15C and then the humidity goes down, so does the potential for branching.  What I also learnt is that the formation of snow is extremely complex (and that intricate details of snow formation are still being researched today.  Bizarrely, snow crystals go from branchy to branchless (even if there is sufficient humidity) in temperature windows and scientists have no idea why this is.  However it is well known that -15c and high humidity is the window for premium light dry powder snow.  So the reason why dry snow hot spots score consistently dry snow is because they consistently hit the right balance of temperature and humidity.  


So why is the interior of North America so good at hitting the 'sweet spot'.  I think its partly to do with the fact that a lot of the mountain ranges, especially in interior USA are small and the mountains don't dramatically exceed each other.  I put it to the forum that I am unaware of any consistent powder hotspots in ski areas that have particularly big snow verticals.  So take the big glacier ski resorts in the Alps for example, the are not known for their consistent dry snow however some of the smaller ones on the edge of the chain, especially the North West where they are first in line for the majority of storms following the jet stream tend to get the driest snow.  Flaine in France is well known, amongst us Europeans at least, for dry powder snow.  I think the case in many parts of North America is the mountains (especially those from the smaller interior chains - especially in the USA) don't significantly loft the weather too high and therefore too cold (and dry).  Take The Sierras in California for example, the majority of the weather following the jet stream has to go over some pretty big mountains, before it gets to the smaller Tahoe ski mountains, I believe the weather has been lofted too high.  Same can be said for Mt Baker, small mountain, surrounded by huge glacier mountains that will loft the weather high but also suck more moisture out which partly explains the huge snowfall phenomenon.  Take Alberta; the Banff ski areas or Jasper, they sit on the edge of the chain and are in direct firing line for a good radius of weather coming in following usual pathway of jet stream.  However somewhere like Whistler has a huge amount of mountains (some of those mountains very big) that weather has to travel over before it reaches Whistler (based on usual pathway of jet stream), i.e coming down from Alaska rather than directly off the coast.  In Russia Krasnaya Polyana, the resort for the 2014 winter olympics is said to get Japan dry snow and lots of it (plus in some seriously burly terrain) that is on the edge of the chain in peripheral mountains that are not dramatically big (no where near as big as the main spine).  The Monashees / Selkirks look pritty good too in that there is a large region of flat land that weather will mostly have to travel over before hitting that chain.  Utah's Wasatch, Bridger Bowl Montana, Taos New Mexico, all on the edge of chains and the mountain ranges of the interior US, small and don't dramatically exceed each other.


Personally I believe this is what constitutes dry snow, it all makes sense, and fits together nicely from my experience.  

I would love to get Tony C in on this as he is for sure the one in the know.  

post #2 of 32
Another thread about this?
post #3 of 32

In general, lower air temps hold less moisture. Higher altitudes hold less moisture. Lower temps can also be because of higher latitudes. Distance from major bodies of water are also a factor. 


Maritime snowpacks (Mt. Baker, PNW, etc..) , relatively low elevation, higher average temps, greater water content per cubic foot of snow.


Continental (CO,WY, etc... ) higher altitude, lower mean temperature, lighter snow.


Japan dry snow is a misnomer... Central Honshu (Hakuba area, etc.. ) is very much a maritime snowpack. Niseko is a bit in between... it's not super high altitude, and the snow isn't generally UT blower light, but most would happily live with higher moisture content if there's commensurately more volume/powder days per season. The northwest lower peninsula of Michigan gets some really nice low moisture content snow, but there just isn't the topography nor snow volume to make it a true destination ski region.  :)  

post #4 of 32
Since you're new and appear to have a legitimate interest, I'll be polite and straightforward:

No reason to drag up an old thread and copy the same op into a new one. Your questions aren't that important and it just makes you look spastic.

No reason to do thread titles in all caps. See sentence 2 above.

A concept to think about: a tl;dr version. Or at least shorter paragraphs.

Welcome, interesting question.
post #5 of 32
Thread Starter 

Yeah I genuinly didn't know how to start a new post, then figured it out after.  Do you think then close this thread and just continue in old thread?

post #6 of 32
Thread Starter 

Plus realised old thread was actually quite old but it seems to be running now.  

post #7 of 32
No worries for this one, it may just result in having to switch between two threads to find your answer ; )
post #8 of 32

...what they all said, plus: the word "constitutes" is used here incorrectly. What constitutes the dryness of snow is simply the water content per volume of snow.  What "creates" , "causes" or "affects" the dryness would seem to be the actual question.


Please don't do this again.

post #9 of 32
Thread Starter 

Ok, so you have a better use of the English language than me.  You knew what I was getting at.  Is there a way I can edit the title and I will?


[title changed at request of OP]

post #10 of 32

paging Mr. Crocker....spill in Aisle 3 (nice post lex007. Recommend use of more paragraphs to save our eyes though)


Last time I put snow in the dryer to find out, someone stole it.

Couldn't believe it!! I come back and it's gone. $1.25 down the drain! Who would steal snow? I guess they're too lazy to go outside and get their own.

post #11 of 32

Some areas favor wetter or dryer snow but you can have dry powder in the PNW and wet cement in UT depending on the specific weather conditions at the time the storm rolls through.  Historically, NM and AZ actually have the least water content on average for snow for many of the reasons OP talked about.

post #12 of 32
Thread Starter 

lol, yeah it wasn't written well, should have pre planned it, just felt the urge to post and posted it.  I thought the same, big para's, too long sentences etc. Sorry, still hopefully I made a few interesting points?

post #13 of 32
Thread Starter 

Actually I originally posted this in an old post; Best resort to ski Powder


Turns out my theory was flawed because although on an altitude comparison the Alps are much colder, but on an actual resort base comparison, the base stations in the Alps tend to be milder.  


That said, going back to the basics of my post; high humidity at a specific temperature window (i.e not to warm, not to cold) is said to make the ideal snow, based on purely snow research, un related to skiing.  I would be interested to see how that ties with the realities of skiing, of peoples understanding.  

post #14 of 32
Don't know beans about dendrite crystals, but I know you talked about crystals branching. We have a somewhat higher humidity here than in Utah. We can have quite cold temps. We grow rime like crazy most of the winter:

While I would say our snow is far drier than the maritime snow west of here, but on the same side of the Continental Divide, it is not as dry as that down in Utah, or even Bridger. We are lower from an altitude standpoint and, of course, west of the Divide.
post #15 of 32
Thread Starter 

That's an amazing picture.  It's seems to follow the tendancy of snow crystals but in conglomoration to form what looks like giant crystals.  Really cool pic!  Thanks for upload.  


Yep, your experience seems to mimic what most peeps report regarding snow quality regions in North America. Would love to understand the science behind it.  From my experience in the Alps, altitude doesn't necesserily mean better snow, but if well shielded snow in colder higher altitude preserves better.  

post #16 of 32
That's a half hour while I was in at lunch. I also have others showing it growing up from groomed corduroy. Will see if I can find them
post #17 of 32

Found pictures of rime growing on a groomed run and on the chair lift:


You can see the feathery crystals growing up from the corduroy.






The end result being this:


post #18 of 32
Thread Starter 

Man they are some amazing pictures.  Which ski area is this?

post #19 of 32
Originally Posted by lex007 View Post

Man they are some amazing pictures.  Which ski area is this?


Whitefish. See the link in my signature for the link to my guide to the resort.

post #20 of 32
Thread Starter 

That's a nice looking hill you have there.  Really nice looking terrain, beautiful trees!  

post #21 of 32
Along with fog for snow preservation. biggrin.gif
post #22 of 32
Thread Starter 

Yeah so cold fog is the catalyst for rime and this appears to be an integral part of the complex process for quality pow.  I wounder, is it often pritty cold at Whitefish?

post #23 of 32

Beautiful photos!


As I understand, that's not necessarily the best for skiing, since it's from high moisture/humidity and the fog particles essentially freezing as ice trails (rime).  Foggy skiing is.......challenging.


But hey, looks beautiful out there, I'd love to go someday.

post #24 of 32

Hey, lex.  Would you please not use all caps in your thread titles?




post #25 of 32
Thread Starter 

Check this out;


"Rime forms on the surface of the snow when super-cooled water in clouds freezes onto the snow surface, trees, chairlift towers or any solid surface. It usually forms when clouds rapidly rise over a mountain range. The air rises so fast that tiny water droplets can't form snowflakes (or graupel in this case) fast enough and the water droplets actually cool well below the freezing level. When they touch something solid, they instantly freeze, thus the spikes grow INTO the wind (as opposed to wind loading in which drifts form on the downwind side)." 


This ties in with my observation that a lot of (but not all) consistant dry pow 'hot-spots' are on the edge of the chain, in the direct firing line of the usual weather-pathway (jetstream).  

post #26 of 32
Thread Starter 

Yeah I know, wanted to change that but don't know how to change title once done.  Do you know how I can change to lower-case?  Thanks

post #27 of 32

I don't think you can change it.  Next time.

post #28 of 32
Thread Starter 

Yeah man, I will do lower case next time for sure.  Force of habit, when I write notes for my self.  

post #29 of 32
Thread Starter 

Personally I think there are a number of factors that influence the percieved "dryness of snow"


I think Tony C is right in that there appears to be a strong corollation with how dry the storm is and how dry the snow is, i.e if weather has crossed several barriers, its striped of precipitation on each round.  


Although I think I have highlighted a couple other factors;


Humidity is needed for crystals to branch
Temperatures need to be cold but not too cold
There is an uncanny concentration of quality pow hot spots on the edge of chains in the direct firing line of usual jet-stream path
Rime is an important factor in 'super-cooling' the crystal so as to maintain for longer and have just learnt; weather that is quickly and rapidly forced upwards, such as weather coming across 'flat land' and hitting a mountain barrier cools very quickly producing rime.  

post #30 of 32
Thread Starter 

And also of course, shielding from wind and sun via mountain blocks or trees and in the case of sunlight, fog all helps preserve whatever grade of snow there is.  But I think we all know this.  

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