A CORRESPONDENT writes:

Even as the remnants of the record snows in the Mid-Atlantic corridor erode day by day, they continue to yield a spectacular harvest of icicles, in all likelihood one of the region’s most abundant ever. I saw one yesterday that appeared to be about 25 feet long, extending from just beneath a third-story window to the top of the snow pack. 

Clearly, or perhaps we should say opaquely, conditions have been ripe: rich raw material; daytime melting, and cold nights. 

Those obvious circumstances notwithstanding, the life of an icicle is surprisingly complicated. It is a self-perpetuating weather system with its own micro-meteorology. Perhaps counter-intuitively, the air in the immediate vicinity of an icicle is warmer than the air a short distance away. When water freezes, it gives up latent heat. Since warm air rises, the warmth creates an updraft from the tip to the base of the icy column. 

Now, for an icicle to keep growing, it needs to be sheathed constantly in a thin membrane of water that flows toward the tip. As it turns out, the aforementioned updraft ends up removing heat from that liquid layer, and some of the water freezes, bonding to the ice mass. 

As the process continues, the icicle grows and grows, and, in some cases, grows and grows and grows and grows.

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