Then, as foreseen in no one’s calculations, the elements took over.

From 1776 by David McCulough. Page 95.

Describing the troops drawn up at Cambridge, waiting for the order to attack, Washington himself said he “never saw spirits higher.”

It was about noon when the first of the British troop transports pushed off for Castle Island and proceeded down the harbor with increasing difficulty against strong headwinds. For by early afternoon, what had been an abnormally warm, pleasant day had changed dramatically. The wind had turned southeasterly, blowing “pretty fresh.” Then, as foreseen in no one’s calculations, the elements took over.

By nightfall, a storm raged, with hail mixed with snow and sleet. By midnight, “the wind blew almost a hurricane.” Windows were smashed, fences blown over. Two of the transports bound for Castle Island were blown ashore. The American lieutenant Isaac Bangs, who was among those freezing at their posts on the high ground of Dorchester, called it the worst storm “that ever I was exposed to.” Clearly there would be no British assault that night.

The morning after, the winds continued to blow with a fury. The snow and sleet had changed to driving rain. General Heath concluded that “kind Heaven” had stepped in to intervene. As so it seemed to many on both sides, when, that morning, Howe called off the attack and gave orders to prepare to evacuate Boston.