In short... Light breeze, not too hot not too cold, very very light rain, and sun rising without rays the next morning.
What are the signs of laylatul-Qadr?
Allaah's Messenger , (SAW), described the morning after Lailatul-Qadr, so that the Muslim may know which day it is. From Ubayy, (RA), who said: that he, (SAW), said: "On the morning following Laylatul-Qadr the sun rises not having any rays, as if it were a brass dish, until it rises up." {Muslim, Abu Dawud, Tirmithi and Ibn Majah}
Abu Hurairah, (RA), said : "We were discussing Laylatul-Qadr in the presence of Allah's Messenger so he said : 'Which of you remembers {the night} when the moon arose and was like half a plate? {Muslim}
Ibn 'Abbaas (RA), said: Allaah's Messenger, (SAW), said: "Lailatul-Qadr is calm and pleasant, neither hot nor cold, the sun arises on its morning being feeble and red." {at-Tayaalisee, Ibn Khuzaimah and al-Bazzaar with a Hasan Isnad}
Narrated by Ubayy Ibn Ka’b, "Zirr Ibn Hubaysh reported: I thus asked Ubayy Ibn Ka’b: Your brother (in faith) Ibn Mas’ud says: He who stands (for the night prayer) throughout the year will find Lailatul Qadr. Thereupon he said: May Allah have mercy upon him. (He said these words) with the intention that people might not rely only (on one night), whereas he knew that it (Lailatul Qadr) was in the month of Ramadhan and it was the 27th night. I said to him: AbulMundhir, on what grounds do you say that? Thereupon he said: By the indication or by the sign which the Messenger of Allah SAW gave us, and that is that on that day (the sun) would rise without having any ray in it." {Muslim}
It was narrated by Abu Salama: "Once I went to Abu Said al-Kudri and asked him, "Won’t you come with us to the date palm trees to have a talk?" So Abu Said replied, "Once Allah’s Apostle performed Iktikaaf on the first 10 days of the month of Ramadhan and we did the same with him. Gabriel came to him and said, "The night you are looking for is ahead of you." So the Prophet SAW performed the Iktikaaf in the middle (second) 10 days of the month of Ramadhan and we too performed Iktikaaf with him. Gabriel came to him and said, "The night which you are looking for is ahead of you." On the morning of the 20th Ramadhan, the Prophet SAW delivered a sermon saying: "Whoever has performed Iktikaaf with me should continue it. I have been shown the Night of ‘Qadr’, but have forgotten the date, but it is in the odd nights of the last 10 nights. I saw in my dream that I was prostrating in mud and water." In those days the roof of the mosque was made of branches of date palm trees. At the same time the sky was clear and no cloud visible, but suddenly a cloud came and it rained. The Prophet SAW led us in the prayer and I saw the traces of mud on the forehead and the nose of Allah’s Apostle. So it was the confirmation of that dream." {al-Bukhari, Volume 1:777}
