Why Does Snow Pack Better Near the Melting Point?

[Charles Link]

Over the last 20 years or more, I have made the observation that the snow for making a snowman only packs properly when the temperature is, in general, above freezing. This could be explained by the unique property of water, which, because it expands upon freezing, the solid phase will melt when pressure is applied. To get the snow to pack well, the temperature of the snow needs to be close enough to the melting point that a slight pressure will melt it, and then it re-solidifies in its new form as the pressure is released. Last Saturday, Chicago had a snowfall that occurred with above freezing temperatures, and I was able to build this snowman in my backyard. He started out at about 5'0", and now stands about 4'0", after a couple of days of partial melting along with sublimation has reduced his height. Anyway, I think I got the physics part correct, but it was fun making the snowman in any case. :) $\\$ Editing: @Chestermiller I welcome your feedback. Do I have the thermodynamics correct on this one, in regard to the snow packing much better near the melting point? :) $\\$ Additional editing: The explanation of the physics of getting snow to pack in this post is later determined to be most likely incorrect, with a different explanation offered by @DrClaude in post 20.

 

[jedishrfu]

Nice snowman. What did you name him?

 

[Charles Link]

Nice snowman. What did you name him?

I didn't give him a name yet, but I think I will call him "Archimedes". :) The weather forecast for Chicago is calling for below freezing temperatures for another week or so, so he should be around for a while. :)

 

[jedishrfu]

Yes and maybe he’ll shout Eureka as he takes a bath in the melt water. :-)

 

[Charles Link]

In case anyone is unfamiliar with how a good snowman is made, especially those in warmer climates, you begin by making a small snowball, perhaps about 6"-8" diameter with your hands. You then take that ball and roll it in the snow, turning it every so often to keep it spherical. If the snow packs well, the ball will increase quickly in size, and it actually gets easier once the snowball gets larger, and the weight of it creates its own pressure to the snow below it that it picks up. (When it is smaller, it helps to press downward to help pick up the snow). A good size for the bottom is about 24"-30" inches in diameter. You first make the bottom, and then do the same with the middle, and then lift the middle onto the bottom portion. The head is the easiest because it doesn't need to be very large. $\\$ And to repeat the observation mentioned in post 1, if the snow is cold, i.e. even a degree or two below the freezing point, it will be very difficult to get it to pack in order to make a good snowman. $\\$ Additional comment: On this one, the snow was only packing moderately well, and it took me perhaps 1/2 hour or more to make it. On a previous one in December, that I made that was slightly larger, the snow was packing exceptionally well, and I built it in about 15 minutes.

 

[jedishrfu]

When I was young I made snow angels then snow men then a snow fort for snow ball battles. We had a lot of fun with our sleds and saucers with the saucers doubling as shields in a snow battle. The fastest downhill thing though was a freezer door. It was so fast and the snow got sprayed in your face as it spun around.

 

[lekh2003]

I have never ever touched fluffy snow. I have been at very high altitudes with cable-cars and trains, but only in the summer, where the snow was basically ice at those heights.

I can't relate to all these wonderful things. Always lived in nice temperate countries (I am well accustomed to heat).

 

[blue_leaf77]

I have never ever touched fluffy snow. I have been at very high altitudes with cable-cars and trains, but only in the summer, where the snow was basically ice at those heights.

I can't relate to all these wonderful things. Always lived in nice temperate countries (I am well accustomed to heat).

An Australian acquaintance of mine once told me that it does snow in some part of Australia, especially those around the center of the continent. You never have winter vacation there?

 

[lekh2003]

An Australian acquaintance of mine once told me that it does snow in some part of Australia, especially those around the center of the continent. You never have winter vacation there?

I have lived, for a large portion of my life, in the Middle East. I have since moved to Australia. It does not snow at all, mostly hail. Of course, we can go up to Blue Mountains or Snowy Mountains, for vacations, but I never had the opportunity.

But I'm 14, I have plenty of time left to go on vacations to all kinds of places.

 

[Drakkith]

I have lived, for a large portion of my life, in the Middle East. I have since moved to Australia. It does not snow at all, mostly hail. Of course, we can go up to Blue Mountains or Snowy Mountains, for vacations, but I never had the opportunity.

But I'm 14, I have plenty of time left to go on vacations to all kinds of places.

No worries. I grew up in Texas, worked in Louisiana for about a decade, and now reside in Arizona, all places that see very little snow on average. I think I remember building a snowman one year when I was a kid, and that single snowman used up all of the snow in our yard.

 

[Charles Link]

Chicago still has cold weather, so the snowman isn't melting yet. Here is a picture of the snowman "Archimedes" on 2-8-18:

 

[Charles Link]

Here is another picture of the snowman that I made on 2-3-18 that I took today, Saturday 2-10-18. Even though we (Chicago) had 10" of snow yesterday, (you can see the additional snow in the picture=I brushed the new snow off of the snowman though), it came down with temperatures several degrees below freezing, and it would have been very difficult to make another snowman because it packs very poorly when the temperature is that much below freezing. For the snowman from 2-3-18, there was only about 1" of snow, but the temperature was just right, (just above freezing), so that it was somewhat easy to make. $\\$ He started out at nearly 5'0" tall, but he is now about 3'6" tall, because of evaporation and partial melting. Temperatures are forecast to be 39 degrees in Chicago on Wednesday, and most likely he will melt on that day.

 

[Charles Link]

The previous snowman melted on Wednesday 2-14-18, but today, Saturday 2-17-18, we had another 1" of snow in Chicago that packed exceptionally well, since the temperature was around 35 degrees, and I made another snowman. This one is about 5' 8" tall. The forecast is predicting temperatures in the 40's tomorrow, so most likely he will melt. Because the snow packed exceptionally well, this one only took me about 15 minutes to make.

 

[DennisN]

I think I remember building a snowman one year when I was a kid, and that single snowman used up all of the snow in our yard.

Here is a little snowman for you (the snowman was not done by me, I found it and took a photo of it a couple of days ago, when we had a little snow):

 

[Charles Link]

Here is a little snowman for you (a photo I took a couple of days ago, when we had a little snow):
View attachment 220590

@DennisN The photo didn't show up. Instead it is a .jpg without a working link. $\\$ Editing: It showed up as an attachment in your quote that I'm responding to, so I can now see it. Very cute. :) And I also can now see it in post 14. Very cute. :)

 

[DennisN]

@DennisN The photo didn't show up. Instead it is a .jpg without a working link.

Thanks! It works on my computer, could you try hitting refresh (F5 or something) on your computer, perhaps?

 

[Charles Link]

Thanks! It works on my computer, could you try hitting refresh (F5) on your computer, perhaps?

See my edited post above. I can see it now. Thanks. :)

 

[Charles Link]

Here is a photo of me with the latest snowman, taken by my neighbor lady. The snowman is about 5'0" tall in this picture, and was about 5'8" tall yesterday. (Temperatures were in the upper 30's today and it is melting a little). Forecast is for rainy and 50's tomorrow in Chicago, so he's likely to undergo a phase change. :) :)

 

[jedishrfu]

You could give him heftier muscles by packing snow on the shovel handles.

 

[DrClaude]

To get the snow to pack well, the temperature of the snow needs to be close enough to the melting point that a slight pressure will melt it, and then it re-solidifies in its new form as the pressure is released.

I think that this is completely wrong. The ability to make snowballs is related to the wetness of the snow. Dry snow is not sticky at all, whatever the temperature, and I think the amount of pressure needed to even partially melt it is beyond what you can achieve with your hands. When the snow is wet, no pressure is needed: simply taking a snowball and lightly putting it on fresh snow is enough to make additional stick to it.

There is often a link between the wetness of the snow and temperature: wet snow usually falls when temperatures are close to freezing. But I have often seen dry snow when the temperature is just below freezing. Likewise, old snow that has been on the ground all winter is rarely sticky, whatever the temperature.

Caveat: all this is based on personal experience of having lived nearly all my life in regions where snow is abundant. I have never dug deeper as to what actually makes snow wet and dry.

 

[jedishrfu]

I remember packing snowballs. The snow had to have a certain consistency. Basically it had to be a little wet and as we packed it, it got more ice like and wouldn't fall apart when thrown.

We also used slushy snow to make ice balls by squeezing the water out and forming an icy ball. We didn't do that too often as slushy balls lead to soggy gloves, then icy cold fingers and time for hot chocolate.

 

[Charles Link]

I think that this is completely wrong. The ability to make snowballs is related to the wetness of the snow. Dry snow is not sticky at all, whatever the temperature, and I think the amount of pressure needed to even partially melt it is beyond what you can achieve with your hands. When the snow is wet, no pressure is needed: simply taking a snowball and lightly putting it on fresh snow is enough to make additional stick to it.

There is often a link between the wetness of the snow and temperature: wet snow usually falls when temperatures are close to freezing. But I have often seen dry snow when the temperature is just below freezing. Likewise, old snow that has been on the ground all winter is rarely sticky, whatever the temperature.

Caveat: all this is based on personal experience of having lived nearly all my life in regions where snow is abundant. I have never dug deeper as to what actually makes snow wet and dry.

I do think that you @DrClaude may be correct. The polar nature of the water molecule might also be part of the mechanism for packing. $\\$One feature of the temperature observation that I have made is that an air temperature of 32 degrees is sometimes too cold for packing, and one explanation is that the snow is colder than the air. Will wet snow pack when the temperature is colder? Then I think it would be more like an ice and snow mixture with very little water, and it might not be very wet. $\\$ The presence of snow,(perhaps different types), along with water and ice complicates any phase diagram that one might try to construct, so I agree, it may be a stretch, and in fact, incorrect to attribute the packing to something going on in the P vs. T diagram. At this time, I think I concur with @DrClaude . $\\$ Editing: Something that might further refute my initial explanation for packing in the OP is, would it be possible to make a snowball even if the P vs. T curve for the solid to liquid line for water had a positive slope, (instead of the negative slope that it has)? And I think the answer would be yes.

 

[DennisN]

We also used slushy snow to make ice balls by squeezing the water out and forming an icy ball. We didn't do that too often as slushy balls lead to soggy gloves, then icy cold fingers and time for hot chocolate.

I remember slushy snow during snowball fights. Snowballs made of slushy snow (non-icy) were a bit like WMDs; semiprohibited, hard to handle by the aggressor, but when fired properly against the target, quite powerful and nasty.

 

[Greg Bernhardt]

I remember slushy snow during snowball fights. Snowballs made of slushy snow (non-icy) were a bit like WMDs; semiprohibited, hard to handle by the aggressor, but when fired properly against the target, quite powerful and nasty.

Essentially turns into ice balls

 

[Charles Link]

@DrClaude appears to have a very good explanation for what is responsible for good packing. In any case, I always enjoy it when the snow conditions are right for making a snowman. As a youngster,(age 6 or 7), I saw my uncle roll a couple of large, (2 feet diameter or more), snowballs to make a snowman. As a teenager, I could never repeat the result. It wasn't until I was perhaps in my late twenties or early thirties that I finally made a good sized snowman, and over the next ten or twenty years, I observed there was a very strong correlation of packing quality to air temperature at or above the melting point. :)

 

[Charles Link]

Here is a snowman I made today, Tuesday 3-13-18, in my backyard in Chicago. The temperature (32 degrees) made for good packing, but there was very limited snow, so this time all I could assemble was a small snowman. He stands about 3'0" high. He might be the last snowman of the season for us, because spring usually means warmer weather and little snow. :)

 

[Charles Link]

Today Monday 4-9-18, we had about 1" of snow in Chicago that was at a very good packing temperature (33 degrees), and I did much better than the previous one. This one is nearly 5'6" tall. :)

 

[jedishrfu]

You'll have to take daily measurements to see how fast he shrinks and how its related to the exposed surface area.

Nice creation too!

 

[jedishrfu]

My preference has been the ice that forms on trees. Its a very beautiful and serene picture of nature in action especially if it drags the power lines down and you now have nothing to watch on TV.

As a kid, sticky snow was great for snowmen, snow forts and snowball battles while dry snow was great for sledding. On becoming a Dad, I began to hate sticky snow because it made shoveling so much harder and was especially troublesome after the snowplow came by (right after you cleared the driveway to go out :-) and dumped a load of heavy packed snow at the entrance much deeper, dirtier and higher than you can imagine. Ugh!

 

[Charles Link]

Here is a photo taken about 6 hours later at 4:30 P.M. With the afternoon sun shining on him, he was leaning tremendously to one side, but I propped him up at the base with some snow that I found in the shade. He has now shrunken to about 4'0" tall, but should survive until tomorrow, with nighttime temperatures below freezing. Tomorrow they are forecasting 46 degrees and sunny here in Chicago, so he will most certainly melt tomorrow. :-) :-)