[The Saucepan Man]

Well, it may be an obvious one (which is perhaps why no one had mentioned it yet), but one of the most striking uses of weather to mirror events occurs as the chapter Helm's Deep unfolds.

The brooding atmosphere is set in the opening paragraphs, as Theoden's company rides towards the fortress:

There were no clouds overhead yet, but a heaviness was in the air: it was hot for the season of the year. The rising sun was hazy, and behind it, following it slowly up the sky, there was a growing darkness, as of a great storm moving out od the East. And away in the North-West there seemed to be another darkness brooding about the feet of the Misty Mountains, a shadow that crept down slowly from the Wizard's Vale.

The clouds are not yet overhead, but darkness is gathering over Mordor and, more pertinently for the purposes of the battle about to unfold, over Isengard. Slowly, the clouds approach:

As the second day of their riding drew on, the heaviness in the air increased. In the afternoon the dark clouds began to overtake them: a sombre canopy with great billowing edges flecked with dazzling light.

There was neither star nor moon when the Riders came to the breach in the Dike ...

And then the storm breaks as the battle commences:

It was now past midnight. The sky was utterly dark, and the stillness of the heavy air foreboded storm. Suddenly the clouds were seared by a blinding flash. Branched lightning smote down upon the eastward hills. For a staring moment the watchers on the walls saw all the space between them and the Dyke lit with white light: it was boiling and crawling with black shapes ... The dark tide flowed up to the walls from cliff to cliff. Thunder rolled in the valley. Rain came lashing down.

The weather here parallels events in a number of ways. The dark clouds gathering at Isengard and approaching Helm's Deep mirror the gathering and approach of Saruman's army. The still, heavy air tells of a coming storm, as the defenders grimly await the coming battle. Thunder and lightning signify the arrival of the Saruman's army, and the lightning is used to illuminate the dreadful force as it approaches. And the rain starts lashing the fortifications just as the Orcs start to assault the fortress. Indeed, their arrows are described as being "thick as rain" as they whistle over the battlements.

Just as the battle seems hopeless, the skies start to clear and the mooon shines brightly. It is said to bring little hope to the Rohirrim as their enemy seems to grow rather than diminish. But, although matters worsen for the defenders, this clearing of the sky does nevertheless preface their ultimate victory.

Gandalf and Erkenbrand arrive just as the sun is rising, and with the battle won, the next chapter opens with:

So it was that in the light of a fair morning King Theoden and Gandalf the White Rider met again upon the green grass beside the Deeping-stream.