Headwater Box Plot: 78 hour Lead
At a 78-hour lead time we have entered phase 3 when the climatologically based QPF is dominating. Compared to the 30-hour lead time, we see an increase in ensemble spread for the low end flow values and a decrease in ensemble spread for the upper 20% of observed values. In addition to the decrease in spread at the high end, we also see indications of an underforecasting bias. This underforecasting bias is seen by the tendency for box plots to be below or mostly below the zero line. This suggests that the hydrologic forecast ensemble spread does not adequately capture the high flow values at a 78-hour lead time when the climatologically-based QPF is a dominant influence.
