York is bracing itself for a potential deluge of overnight rain, with torrential thunderstorms forecast to hit the Knavesmire.

The going had already been changed to good, good-to-soft in places before racing began on Wednesday, meaning there is every chance conditions could become really tough if the forecasts prove accurate. Rain-softened ground of that kind asks different questions of runners than the quicker surfaces more typical of high summer, placing a premium on proven stamina and an ability to handle cut in the ground.

The feature contest on day two of the Ebor Festival — York's flagship four-day August meeting, which also stages the Juddmonte International, the Nunthorpe and the Ebor Handicap — is the Group One Yorkshire Oaks (3.35pm), the fillies-and-mares showpiece run over the same mile-and-a-half trip as the Epsom Oaks, in which this year's Classic generation has the chance to measure itself against the elders.

One mare looks likely to take all the beating: KALPANA, who will relish any rain and is available at 6/5 with bet365. She brings by far the strongest form to the table courtesy of her most recent victory in the King George VI and Queen Elizabeth Stakes — Britain's premier all-aged middle-distance race, run at Ascot in late July — undoubtedly the best performance of a career that also includes two Group One victories before that success, as well as several creditable performances at the highest level.

A credit to her connections for her consistency, she has finished out of the top three just once in 17 starts. Seeing off the likes of Calandagan and Benvenuto Cellini most recently is top-class form, and she will not need to hit that level to win here.

Last year's winner MINNIE HAUK can bounce back from an abject performance last time. The Aidan O'Brien-trained filly looked one of the best around in her three-year-old campaign, landing both Classics — the Oaks double at Epsom and the Curragh — before this contest and producing a huge run when second in the Arc at Longchamp, Europe's most prestigious all-aged race. She has not quite kicked on this year, but ran a near career best behind Ombudsman in the Prince of Wales's Stakes over ten furlongs at Royal Ascot, a trip two furlongs shorter than Thursday's test and one that looks on the sharp side for her. It may be wise to put a line through her King George run last time, and if she rediscovers her form she is the main danger.

The pair look the obvious two for a Quinella with World Pool, the internationally commingled tote pool through which bets such as the Quinella — naming the first two home in either order — are offered, but it may be worth adding pacemaker SUGAR ISLAND, who may just be in the right spot out front at 150/1 with Paddy Power. She will relish conditions if they get really bad and could easily hit the frame.

Pointers — Thursday

• Kalpana — 3.35pm, York Ebor Festival
• Sugar Island (each-way) — 3.35pm, York Ebor Festival
• Kalpana, Minnie Hauk, Sugar Island (Quinella) — 3.35pm, York Ebor Festival