What are the enemies of snow?

[billski]

Help me out with a list, going from worst to best. Please rank for me precipitation events, from worst to best that wreak the worst damage to the snowpack. I'm defining "damage" as reduction of snowpack, or anything that makes it less ski-able (like ice).

I'll take a stab at it based on my pedestrian understanding. I know there are other variables like sun and temperature and winds, but I'm trying to keep it simple for my simple brain.

Most Damage to snowpack
..
Fog
Freezing Fog (whatever that is)
Freezing Rain
Rain
Sleet
Hail
--- the line where we move from damage to base-building. Is this right?
Wet Snow
Dry Snow
..
Least Damage to snowpack

did I get it right? What did I miss? Thanks.

 

[Greg]

I hear a lot how fog melts snow. It's my understanding that the fog is a result of melting snow, i.e. warm moist air over the cold snowpack. Bottom line is warmth is the biggest enemy of snow, whether from a southerly flow or the sun. Warm wind just amplifies the problem since it mixes the air thus causing you to lose the cold layer near the surface.

 

[awf170]

Greg is correct. Here is my list.


Warmth + rain + wind
rain + warmth and wind + warmth
rain or warmth or wind (if there is powder on the surface)
---------------------------------------------------------------------------------------------------------------------------
Freezing rain (despite making conditions awful I think it does help with base building)
Powder (really doesn't do anything for the base unless you get huge quantities)
Sleet (wicked good base material, but still might not cover large rocks, down trees, stumps, etc)
Dense snow (equal to sleet in base building ability but will also cover lurking objects in the woods)

 

[dmc]

communism...

 

[GrilledSteezeSandwich]

People from Jersey..since they skid their turns and scrap it down to the ice..

 

[cbcbd]

I don't see how sleet, hail and freezing rain lower the snowpack...
Sleet is wet, but still accumulates, and with a freezing after it should add to the snowpack, although not a fun add.
Same for hail and freezing rain - they don't lower the snowpack, they're just not the ideal additions to the snowpack for skiing.

Also don't see how wind should negatively affect the snowpack other than blowing powdery snow off a particular slope. If it's warm or raining, wind should only "help" by lowering the windchill and helping the precip to go away from the liquid kind.


Rain is the worst. Rain at 35 degrees is worse than 60 degree weather with no rain.

 

[awf170]

If it's warm or raining, wind should only "help" by lowering the windchill and helping the precip to go away from the liquid kind.

When it is warm, but not windy a thin layer of cooler air forms above the snowpack. So even if it is 60 degrees there could be a layer at the surface of 40 degree air. If it is windy that layer won't be able to form and the snow will constantly be hit with the 60 degree air.

 

[Greg]

Also don't see how wind should negatively affect the snowpack other than blowing powdery snow off a particular slope. If it's warm or raining, wind should only "help" by lowering the windchill and helping the precip to go away from the liquid kind.

Wind chill has nothing to do with actual temperature. Windchill is an estimate of how it "feels" to exposed skin.

Again, wind will mix colder layers at the surface with warmer layers aloft, effectively raising the temperature closer to the snowpack where it does the most damage.

Rain is the worst. Rain at 35 degrees is worse than 60 degree weather with no rain.

Disagreed. Cold rain can just drain through. 60 degree temps will eat snow.

 

[KingM]

The Christmas one was a brutal example of this kind of stuff. It warmed to rain, then the rain went away and was followed by extreme warmth and wind. The end result was the almost complete annihilation of the snow pack over the course of what? 36 hours?

 

[dmc]

I don't see how sleet, hail and freezing rain lower the snowpack..

that would depend on the snowpack itself.. temp and water content...

 

[cbcbd]

When it is warm, but not windy a thin layer of cooler air forms above the snowpack. So even if it is 60 degrees there could be a layer at the surface of 40 degree air. If it is windy that layer won't be able to form and the snow will constantly be hit with the 60 degree air.

Ok, I can see that.

Wind chill has nothing to do with actual temperature. Windchill is an estimate of how it "feels" to exposed skin.

Again, wind will mix colder layers at the surface with warmer layers aloft, effectively raising the temperature closer to the snowpack where it does the most damage.

Disagreed. Cold rain can just drain through. 60 degree temps will eat snow.

And wouldn't then the precipitation also feel the same temperature as exposed skin? I know wind chill is not the actual temperature, but it affects everything hit by that wind since it removes heat more effectively from objects that have energy, right? Anyone take physics recently and can school us?

As for the rain... from what I have seen I still think rain will cause more damage. But then again, I would really have to get my physics books from HS out to really check this one since there are so many variables if you were to compare the two... I think I'm just going to step out of this one.

 

[dmc]

they teach all this stuff in AVI class... Or a lot of it...

 

[cbcbd]

I took Avy 1 and it was mostly about the basics - triggers, the avy triangle, traps, planning, route finding, beacon use, etc.
At least from what I was told, Avy 2 went more into the snow science part of it.

 

[dmc]

I took Avy 1 and it was mostly about the basics - triggers, the avy triangle, traps, planning, route finding, beacon use, etc.
At least from what I was told, Avy 2 went more into the snow science part of it.

AVIII get more into it for sure...

 

[Greg]

And wouldn't then the precipitation also feel the same temperature as exposed skin? I know wind chill is not the actual temperature, but it affects everything hit by that wind since it removes heat more effectively from objects that have energy, right? Anyone take physics recently and can school us?

I'm not a meteorologist, but wind is a result in changes in air pressure. It doesn't have any effect on changes in temperature per se. That's really an effect of wind direction as you probably know (northerly = cold, southerly = warm, at least in this hemisphere ). So if you're on the backside of a departing high pressure system (spins clockwise) you'll get wind from the south which will usher in warm air.

Anyway, right - windchill is just an estimate of how it feels. A warm wind blowing on a cool surface probably does warm it faster and vice versa probably is true. I'm not a physics guy either, but I do know that wind doesn't inherently "cool". It depends on the temperature of the wind and the surface it's hitting as to whether it accelerates heat loss or gain.

 

[polski]

My experience this season is that far and away the biggest enemy of snow is a Storm Speculation thread.





Sorry, couldn't resist.

On a more serious note, I suspect hail is rarely if ever a positive factor for skiing base because it forms in strong thunderstorms, which tend to happen outside of ski season. Even if there were a severe tstm on the shoulders of the season, like in the spring, hail at the front of the system almost certainly would be followed by heavy rain. I know there's occasionally "thunder snow" (some was forecast in SNE on New Year's Eve in fact, though I didn't hear any thunder while I was out that day) but you need lower-level warmth to feed the instability for the kind of strong tstm that could produce hail.

 

[snoseek]

Does sun fall into tempature?

 

[tcharron]

I hear a lot how fog melts snow. It's my understanding that the fog is a result of melting snow, i.e. warm moist air over the cold snowpack. Bottom line is warmth is the biggest enemy of snow, whether from a southerly flow or the sun. Warm wind just amplifies the problem since it mixes the air thus causing you to lose the cold layer near the surface.

An additional issue is that fog allows the humid air to maintain tempurature, potentially causing more sublimation. I'd asked a simular thing on some forums a while back, and it came down to, when the fog conditions happen, a nasty cycle begins, where more fog is made, where more snow turns to fog, etc..

 

[Greg]

An additional issue is that fog allows the humid air to maintain tempurature, potentially causing more sublimation. I'd asked a simular thing on some forums a while back, and it came down to, when the fog conditions happen, a nasty cycle begins, where more fog is made, where more snow turns to fog, etc..

Makes sense.

 

[Marc]

Ok, I can see that.


And wouldn't then the precipitation also feel the same temperature as exposed skin? I know wind chill is not the actual temperature, but it affects everything hit by that wind since it removes heat more effectively from objects that have energy, right? Anyone take physics recently and can school us?

As for the rain... from what I have seen I still think rain will cause more damage. But then again, I would really have to get my physics books from HS out to really check this one since there are so many variables if you were to compare the two... I think I'm just going to step out of this one.

Somebody call me?

If wind becomes a net help or hinderence to the heat transfer to a snowpack depends on the temperature of the snow pack and the air.

If the air is warmer than the snowpack, wind will add heat to the snow pack faster by convective transfer.

If the air is colder than the snowpack, it will remove heat faster from the snow pack than stagnant air because of convective transfer.

All other conditions being equal, naturally.

Also, fog damages a snow pack so badly because much of the radiative energy emitted from the snowpack (mostly the infrared range of the spectrum) is reflected by fog (really just a water in air suspension). That's why clear nights in the winter are often colder than cloudy nights. All the radiation eminating from earth bound surfaces is lost to space with very little gain (stars... moon... tinker toys compare to the sun). Clouds will reflect that back.

They other reason fog is killer is because of high humdity. Humidty, as Greg sort of touched on, sets up a loop of melting and evaporation/sublmation that creates more fog as the conditions persists because of the radiative feed back, and because of the higher capacity for conduction that humid air has compared with try air. The more humid the air, the better at transferring heat it is.