A cold front Saturday morning stretching from southern Iowa to northern Virginia may serve as the trigger for storms in Kentucky Saturday afternoon (National Weather Service)

Warm, humid air will be firmly in place over the Tennessee Valley, with afternoon highs expected in the mid-80s. Meanwhile a cold front lurking to the north near Kentucky’s border with Ohio may sag south. The potential clash of the air masses means a 40% chance of showers and thunderstorms.

Writes the National Weather Service in Louisville, Kentucky:

Models are indicating a back-door front will edge into the forecast area by as early as Saturday afternoon, which could trigger more sustainable convection. Either way, heavy rain, wind, and small hail appear to be the main threats at this time.

Accuweather’s a little more optimistic in its forecast:

Indications are that the core of the rainfall will tend to shift to the south of the area during the afternoon and evening Saturday. But, there can still be stray storms and downpours left behind the main mess.

Additional storms are possible on Friday and Friday night, prior to Saturday’s “run for the roses”, potentially muddying up the track.

Historically, rain is common on race day. Of the 137 Derby Days, 46 percent have received rain at some point according to the National Weather Service.

Yahoo notes the Kentucky Derby has never been canceled due to weather.

Here are some more Kentucky Derby weather factoids, courtesy the National Weather Service in Louisville - which has published a complete history of Kentucky Derby weather conditions:

Coldest temperature: 36° May 4, 1940 and May 4, 1957
Coldest high temperature: 47° May 4, 1935 and May 4, 1957
Coldest average daily temperature: 42° May 4, 1957
(The cold temperatures on May 4, 1957 were accompanied by 20 to 25 mph north winds!)

Warmest temperature: 94° May 2, 1959
Warmest low temperature: 72° May 14, 1886
Warmest average daily temperature: 79° May 14, 1886
Wettest: 2.31” of rain May 11, 1918

Frozen precipitation: On May 6, 1989 sleet was observed from 1:01pm to 1:05pm.

Out of the 137 Derby Days, 63 (46%) experienced rain at some point during the day.

Longest stretch of consecutive wet Derby Days: 6 (1989-1994)
Longest stretch of consecutive dry Derby Days: 12 (1875-1886)