Officials at Aintree have today said they have no plans to water the course until at least early next week following the forecast of rain this weekend.
And bookmakers Coral are anticipating the possibility of soft going for the Martell Grand National a week on Saturday following support for Edmond in the contest.
Showers are forecast from Saturday afternoon with the chance of sleet and strong winds on Monday and Tuesday.
Clerk of the Course Ian Renton said today: "We would certainly anticipate rain over the weekend which we would welcome as without it the Mildmay and Hurdle courses would be on the fast side.
"At this moment there is no plan to water and will wait to see what happens over the weekend."
The going at Aintree remains good, good to soft in places on the National course and good on the Mildmay and Hurdle courses.
Trainer Henry Daly said on Wednesday that Coral Welsh National winner Edmond was an unlikely runner in the National due to the likelihood of fast ground.
However after "serious support" Coral has cut Edmond to 12-1 from 16-1 and has also trimmed fellow mud-lovers Young Kenny (10-1 from 14-1), Hollybank Buck (25-1 from 33-1) and Kendal Cavalier (20-1 from 28-1).
Coral spokesman Simon Clare said: "The whole shape of the Grand National betting depends entirely on the weather and the latest information suggests soft ground at Aintree is now odds-on.
"If the heavy rain arrives at Aintree this weekend, Young Kenny and Edmond will be vying for favouritism by Monday."
Other ante-post moves in the National have seen William Hill cut Djeddah to 16-1 from 25-1, while Ladbrokes make The Last Fling 16-1 from 20-1 and Esprit De Cotte 40-1 from 66s.
The likelihood of rain will please trainer Venetia Williams who has confirmed Kingdom Of Shades on course for the Aintree spectacular.
The gelding, twice a winner this season including the four-mile-one-furlong Miles Gosling Handicap Chase at Cheltenham in January, has not raced since unseating Brian Crowley in the Tote Northern National at Newcastle last month.
Miss Williams said: "He's fine and the plan was to go straight for the Grand National.
"He wouldn't want fast ground but I can't remember the last time it was fast ground on the National course."
Meanwhile jockey Andrew Thornton, currently sidelined with a leg injury following a fall at Wincanton last week, is hoping to ride the Philip Hobbs-trained Stormy Passage in the National.
"He goes very well fresh. He was second in the Murphy's Gold Cup on his first run so if he could run up to anything near that he wouldn't be a forlorn hope," he said.
"He's got plenty of experience under his belt, he's the right sort of age for the race, he'd like good ground and he's got a nice weight.
"Obviously the trip's a question mark but you don't know until you try so I'd be hopeful of a good ride." Timmy Murphy has been booked to ride the Paul Nicholls-trained Flaked Oats.
His agent Chris Broad said tonight: 'Timmy is excited about the ride as the horse ran well last time and he's looking forward to a big run.'
The 11-year-old, a 33-1 chance with Ladbrokes for the Aintree marathon, was runner-up to Ackzo in the Midlands Grand National at Uttoxeter on his latest start.
Latest Martell Grand National betting:
Coral: 9-1 Star Traveller, Bobbyjo, 10-1 Young Kenny, 12-1 Edmond, 14-1 Micko's Dream, 16-1 Bettys Boy, 20-1 Kendal Cavalier, Cavalero, The Last Fling, 22-1 Djeddah, 25-1 Hollybank Buck, Dark Stranger, Niki Dee, Red Marauder, 33-1 Bar.
Ladbrokes: 7-1 Bobbyjo, 8-1 Star Traveller, 14-1 Betty's Boy, Djeddah, 16-1 Micko's Dream, The Last Fling, Young Kenny, 20-1 Red Marauder, Dark Stranger, Cavalero, 33-1 Bar.
William Hill: 8-1 Bobbyjo, Star Traveller, 14-1 Bettys Boy, Young Kenny, 16-1 Djeddah, Micko's Dream, 20-1 Cavalero, Edmond, The Last Fling, 25-1 Dark Stranger, Earthmover, Red Marauder, 33-1 Bar.
