The featured chart is a time series of air temperatures from Sioux City (red) and Des Moines (blue). A cold front is currently pushing thru the state and you can see from the chart how it passed Sioux City first and then Des Moines by the lag in time for the temperature drop. Highs will be around 20 degrees cooler than yesterday, which will be closer to seasonal values for this time of year.

Voting:
Good = 16
Bad = 2