"Sunday evening's figures give the second episode of Top Gear a 14% share of all television viewing in its timeslot.
BBC One's Antiques Roadshow attracted more viewers than the motoring show - with 4.2 million people tuning in."
That's from a BBC news article
http://www.bbc.co.uk/news/entertainment-arts-36458510Evans doesn't think it's relevant, though:
"Overnight television viewing figures for Top Gear have never been less relevant. Obviously some newspapers prefer to live in the past." (from his Twitter account).
Weather probably did play a part, but I'm not so sure it will have played enough of a part to justify that level of drop.