Double Olympic bronze medallist Tina Cook hopes the wet British summer will not play havoc with riders in Monday's crucial London 2012 eventing cross-country test.
Cook and her Great Britain eventing team-mates, who include Zara Phillips, hold third place in the team competition after dressage.
The British quintet are 7.9 penalties behind leaders and gold medal favourites Germany and 4.9 adrift of Australia, with Sweden and New Zealand tied for fourth.
Germany-based Japanese rider Yoshiaki Oiwa is the shock overnight individual leader on a score of 38.10. Italian Stefano Brecciaroli is second and 56-year-old New Zealander Mark Todd, who is chasing his third Olympic title, lies one place behind.
Mary King and Imperial Cavalier remain the highest-placed British combination in 12th. Cook and Miners Frolic are 14th, William Fox-Pitt (Lionheart) equal 17th, Phillips (High Kingdom) equal 24th and Nicola Wilson (Opposition Buzz) equal 39th.
Cook was faced with torrential rain, thunder and a threat of lightning during her dressage test in the main arena at Greenwich Park.
Sweden's Niklas Lindback - the next competitor after Cook - was delayed for 10 minutes by ground jury president Anne-Mette Binder as conditions deteriorated.
But New Zealander Andrew Nicholson, the world number two, blasted the weather hold as an "absolute disgrace" and claimed that decision had affected his preparations.
Cook coped superbly with the elements, though, as her score of 42 penalties kept Britain firmly in the mix for medals.
Attention now turns to course designer Sue Benson's 28-obstacle cross-country track through the hilly and twisting terrain of Greenwich Park, and it promises to have a considerable effect on where medals - team and individual - will end up.
"I have been eventing for 20-odd years and you do get this type of weather thrown at you," Cook said.
"Unfortunately, we can't stop the competition and say 'I don't want to do it now'.
"At the Olympic Games, you hope you are not going to have rain, thunder and lightning thrown at you, but I did and I had to deal with it. We live up on the South Downs in Sussex getting blown away.
"We just hope it doesn't rain too much tomorrow because it will be very slippery around those corners on the cross-country course.
"The horses do have studs in their shoes, but if horses are slipping then you will just have to steady around some of the corners, so therefore time faults will rack up.
"I think the time (10 minutes, three seconds) will be tough to get, and the riders are all aware of that.
"I think the time is gettable, but less so if we get rain because with there being so many turns you will just have to be a bit cautious in places.
"It will be fast, furious and exciting, anyway."
Cook's dressage performance came after the Queen's granddaughter Phillips marked her Olympic debut with a solid score of 46.10 on High Kingdom. Phillips' audience included her mother the Princess Royal and grandfather the Duke of Edinburgh.
"It was incredible, an amazing feeling to be part of the Olympics and ride for your country," Phillips said.
"The horse coped well with the crowd. He is very chilled and getting stronger all the time."
Cook, though, arguably produced one of the day's most accomplished tests, given what was thrown at her.
"I am used to riding him in the rain at home. I don't have an indoor school, and I have ridden in some very wet days on the South Downs," she said.
"But the noises when the judge's box roof looked as though it was going to come off when he was doing his extended trot, I really hoped he was not going to spook.
"I am just really pleased that the horse kept a lid on it and tried his best. I would have loved the sun to be shining down on me - it would have been brilliant - but that's England for you."