Dirty snow (snirt) & melting point

[Mephisto]

You know that dirty disgusting snow that accumulates on sides of roads over the winter, and then doesn't melt until well into May or something? Why is it that this snow refuses to melt? It mixes with dirt and exhaust fumes from the cars, and somehow becomes really hard and un-meltable.

Does anyone have an explanation? Its much darker, so it should absorb light much more easily and melt even faster! Its a puzzle :(

 

[Dr Lots-o'watts]

I thought the dirty snow left in May was simply what was left of the highest and most shaded snow banks of the previous winter. I have no reason to assume a different melting rate for the late snow I see in my area.

 

[russ_watters]

If it's not in the sun, it absorbs heat via convection, which is a pretty slow process. I have some fresh looking snow on my deck that never seems to melt.

 

[Ranger Mike]

I think due to snow plows pushing the snow to the burm, many times, you have a layered effect and snow is "packed" thus denser relative to soft fallen snow around the packed snow..all things are relative and it takes mucho time to melt a packed snow mass..
also there may be severla thawing freezing cycles for the curb side snow pack and will make melting more difficult