Hey, so after implementing the changes with rounding and converting to integers the start-up script should now look like this.
clean_data=read.csv("ncdc_galesburg_daily_clean.csv",stringsAsFactors=FALSE)
clean_data$Date=as.Date(clean_data$Date)
require(zoo)
clean_data$PRCP[is.na(clean_data$PRCP)]=0
clean_data$TMAX=na.spline(clean_data$TMAX)
clean_data$TMIN=na.spline(clean_data$TMIN)
## See Exploring Daily Avg Temperatures
clean_data$TMAX=as.integer(round(clean_data$TMAX))
clean_data$TMIN=as.integer(round(clean_data$TMIN))
clean_data$avgTemp=((clean_data$TMAX+clean_data$TMIN)/2.0)
require(xts)
avgTempXTS=xts(x=clean_data$avgTemp,order.by=clean_data$Date)