On bar charts, to better distinguish between cases where the data zero vs when there is no data, the bar should be greyed out.
Note: the charting package does not support this function at this time.
For some locations hourly precipitation/rainfall/snowfall data is available. It would be great to have charts on that.
Provide a graph of wind direction over time. See http://nsc.ca/wind/graph_wind_2hr.php for example. There are many varying requests for this type of information.