Seasonal Volume Visualization

The seasonal volume visualization provides dashboard users with a quick seasonal volume comparison and a deeper look into the probabilistic forecasts to answer questions such as:

• How has the projected seasonal volume evolved over the past month?
• What is the likelihood that this year’s seasonal volume will be below, above or around the long-term average volume?

Here's an example plot from the HydroForecast Dashboard that computes the seasonal volume from March 5th to June 3rd, 2025, assuming the current day is April 4, 2025. Let's break it down by plot in the next sections.

How Seasonal Volume Predictions Evolve Over Time

This shows box plots of seasonal volume. The left box plot shows the historical seasonal volume from March 5th to June 3rd, showing the distribution of volume from years 2000-2022. Within the box plot there is a solid line which shows the historical median and a dashed line which shows the historical mean. As with typical box plots, the top of the box represents the upper quartile (e.g., 75% of historical data was below this value) and the lower box represents the lower quartile (e.g., 25% of historical data was below this value). The whiskers extend to show the historical minimum and maximum observed values but does not include data considered as an outlier.

The three blue box plots on the right show the predictions of seasonal volume made by HydroForecast. The labels on the x-axis are the forecast issue dates for each of the three forecasts. Since the volume is computed from March 5th to June 3rd, some time has already passed since predictions were issued. We show that contribution of time in the past, or rather the already observed volume in the gray box. 

The forecast furthest right is the latest forecast. In this example, the forecasted median is higher than the historical median, but the forecasted mean is similar to the historical mean. Overall we find that as the season progressed, predictions for seasonal volume increased over time. On March 8th, HydroForecast predicted mean flows around 1.0M acre feet, which steadily increased to a mean prediction of 1.6M acre feet for the forecast issued on April 4, 2025.

While this plot above is shown as units of volume in acre feet, users can also select from the Volume dropdown to view as a % of long-term average (LTA). 

How Seasonal Volume Predictions Compare to the Long Term Average

This plot shows the likelihood of high, normal or low volumes over the selected time period compared to the LTA. This plot always shows the probabilities that the latest issued forecast will be below the LTA (grey bar), similar to the LTA (blue bar), or higher than the LTA (purple bar). In this plot, we see flows are mostly predicted to be similar to the long-term average with around a 40% chance that flows are within 90-110% of the LTA.