I am not even sure it would be helpful to gather info on the highest DP of a given day. Rain causes the RH to go up obviously but raining into relatively dry air at the surface will cause the temp to fall and DP to rise a bit. So we could have a day with DP's in the 50's, we get a shower, and the DP rises to the 60's for a bit and then back down when the shower is over...but that day is then recorded as a 60's DP day.