LOUISVILLE, Ky — The sun will not shine bright on the old Kentucky track on this Derby Day. Saturday’s 143rd edition of America’s rite of spring will feel more like November. It will be overcast at soggy Churchill Downs, with temperatures in the low to mid-50s and a 70-percent chance of occasional showers, and maybe even a thunderstorm or two.

That would be an improvement on Friday, rain-soaked Kentucky Oaks Day. To paraphrase W.C. Fields, it was “not a fit day out for man or beast,” but the show went on anyway. With umbrellas banned for safety reasons, elegantly attired fans draped themselves with see-through plastic ponchos and drank mint juleps.

According to weather.com, there’s only a 6 percent chance of precipitation two hours before the Derby’s 6:46 post time. A sloppy or muddy surface maximizes confusion in a race that annually bedevils serious and casual horseplayers. It would be only the 43rd Derby run on a track not rated fast.

Among the field of 20, only six — 4-1 morning line favorite Classic Empire and long shots Battle of Midway, Hence, Tapwrit, Thunder Snow and Gormley — have won on a wet surface. Five lost their only try, and it will be a new experience for nine.

Then again, Orb never had raced on a wet surface but won the 2013 Derby anyway, coming from far back on a sloppy track to begin a streak of four winning favorites. That hadn’t happened since the 1970s, and the post-time betting choice hasn’t won five in a row since the 1890s. The favorite paid off from 1891-96, when a total of only 30 horses competed.

Handicapping on pedigree is a tricky business, and there’s no guarantee that a son will repeat his sire’s success on wet tracks. Orb’s father was Malibu Moon, a prolific producer of slop runners. Irish War Cry’s sire is two-time Horse of the Year Curlin, who dominated the 1 1⁄4-mile Breeders’ Cup Classic in 2007 on a weekend when a monsoon engulfed Monmouth Park.

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Trainer Graham Motion won the 2011 Derby with Animal Kingdom, who never had raced on conventional dirt. Motion hopes “like father, like son” applies with Irish War Cry. The late Polish Numbers, the colt’s maternal grandsire, was a standout off-track sire.

“His daddy handled a sloppy track well, and he looked good galloping on it [Friday],” Motion said. “He’s had a good week here, so we’re hopeful.”

Unlike Animal Kingdom, who paid $43.80, Irish War Cry is the 6-1 morning line fourth choice and a popular pick.

“Animal Kingdom was basically under the radar,” Motion said. “It’s a little bit different this time around because he’s one of the liked horses. This is the first time I’ve come here with a horse who’s considered a real contender. It’s definitely a different situation, but I don’t feel a lot of pressure. I feel really comfortable with him.”

Notes & quotes: There were no scratches by Friday’s 9 a.m. deadline, so the two Derby also-eligibles, Royal Mo and Master Plan, will not run, even if a horse is withdrawn.