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This visualization has been developed to illustrate how snowpack changes in water supply basins throughout Colorado in a water year. The goal is to quickly gain an understanding of both the absolute and relative magnitude of water supply throughout Colorado. The visualization illustrates how conditions in local and major basins vary in time and compare to each other. The basins correspond to those used by the National Weather Service (NWS) River Forecast Centers (RFCs) and Northern Water. ABRFC = Arkansas Basin, CBRFC= Colorado Basin, MBRFC = South Platte (Missouri) Basin, NCWCD = Northern Water collection basins, WGRFC = Rio Grande Basin (West Gulf RFC). See also the map interface to SNODAS data hosted by the Open Water Foundation (in process of moving to a State of Colorado server) - use this to learn more about locations of the basins.

SNODAS snow data are estimated using remote sensing, calibrated with on the ground measurements including SNOTEL. Unlike SNOTEL sites, which can only measure snow at specific locations, SNODAS provides estimates of Snow Water Equivalent (SWE) and snow cover throughout the United States. It is important to recognize that SNODAS data are not consistent across time because the algorithms used to estimate computed values have changed over time, and SNODAS data are only available since water year 2004. However, these facts are ignored in this visualization in order to leverage SNODAS and illustrate the utility of the dataset.

The visualization is configured to plot snowpack data for each local basin as 'bubble' markers on the chart. Daily SWE values are displayed during the period of a single water year. This visualization displays 3 separate variables across time, explained below. The markers move across the chart to show 2 variables (x and y), while also varying in size, representing a third variable.

  • X-axis is the cumulative SWE volume in each local basin, in acft, essentially the amount of precipitation as snow that has fallen on a basin during the water year. This is a measure of seasonal water supply and is contrast to daily "SWE on the ground" data products that are traditionally used to indicate potential future runoff from the snowpack. The cumulative value gives a broader indication of seasonal drought and water supply from the full hydrological system, including snow that has melted and is present in the ground (as can enter the stream later), has run off as streamflow and is observed in streamflow measurements, and has evaporated, ablated, or sublimated into the atmosphere.
  • Y-axis is the corresponding cumulative SWE in each local basin, as percent of mean. Cumulative SWE is used to limit the amount of ups and downs from one day to the next and to provide a better evaluation of the entire water year. A horizontal line is emphasized at 100% to indicate mean of historical SNODAS daily values for all years.
  • The size of the marker indicates the cumulative total SWE for the local basin and all upstream basins (total upstream drainage area). Therefore, the largest marker in a basin color group indicates the most downstream local basin in that group. An organization that is evaluating its water supply could, for example, determine the most downstream basin in its water collection watershed. The size of the marker will indicate the total amount of snow precipitation that has accumulated on the upstream basins. The total amount is also indicated in the data view area. The relative y-axis position of the marker for that basin will indicate whether or not the water supply situation is below, at, or above the mean for historical SNODAS data. A relatively small marker below the 100% line means that the local basin and the total upstream basin are both "dry" (bad news). A relatively large marker above the 100% line means that the local basin and the total upstream basin are both "wet" (good news).

The choices of values for each axis and marker size could be altered to create other data visualizations. OWF welcomes feedback on this visualization and suggestions for new visualizations. Additional variable combinations may be provided in the future.



The legend on the upper right side of the visualization doubles as a tool to select markers for larger basins, grouped by color. Selected markers are shown in normal colors whereas non-selected markers are transparent. In this visualization, the grouping is by River Forecast Center basin and Northern Water system basins, Single-click on a legend symbol or its text label to select a basin group to highlight. Use Ctrl-click to select additional basins. Use the 'Select all Markers' button to select all groups.


Local Basin Selection:

The dropdown/search menu on the right side of the visualization (below the group selector) allows specific local basins to be selected. Markers can be toggled on or off. It is also possible to highlight specific markers on the visualization by clicking on them once (multiple markers can be selected in this way). Re-click on a selected marker to deselect the specific marker.


Toggle Annotations:

The visualization defaults to not show annotations, which are notes that are shown at specific times to explain the data. If annotations are included in the dataset and are enabled, then annotations can be enabled and will be displayed below the time scrollbar. Annotations are currently not available for this dataset.


Toggle Tracer:

The visualization defaults to not show tracers. Tracers can be toggled on, which will result in a line showing the path of a marker as it moves through time. Tracers can be overwhelming for a large number of markers; therefore, consider using only when specific basins or markers are selected.


Water Year Selector:

The visualization defaults to showing the most recent water year. Historical water years can be selected, which will cause the visualization to refresh the data. If a water year has missing data after a day, the animation will stop at the last day that has data.


Time Slider:

The time slider at the bottom of the visualization is interactive. Drag the slider to move the visualization across points in time, or use the controls located below the time slider to play, pause, replay the visualization, or move the visualization forward/backward a day in the year. Moving the slider across time too quickly will reflect in the tracers that track the data, and may result in unexpected behavior through the display of the tracers. Clicking anywhere on the time scale will reposition the animation at that day. A vertical jump in the animation corresponds to a snowstorm that immediately increases the absolute and relative magnitude of snowpack. The position of markers tends to settle down in summer given that little additional accumulation occurs.


Speed Slider:

Click and drag the Speed slider to change the speed at which the visualization will play.


Data Values/Interpolation:

At the bottom left of the visualization is the data view area. Hovering over a marker will cause the associated data for the marker at the current display time to be shown the data view area. The visualization interpolates across all points of time to fill in data points in order to fluidly display the animation. However, the data view area will only display the raw data used as the input for the visualization. For this dataset, SNODAS data are typically available for each day, other than when the SNODAS system is offline and for the end of the water year after the current day. Therefore, actual, rather than interpolated values, are shown. The units of time on the time slider are the same as the intervals for the input data (day).



The annotation view area below the visualization on the right displays data annotations that explain he data. The SNODAS visualization does not currently contain annotation data but these could be added to explain the dataset, for example to note unusually large storms or high temperature/melt events.


The input data for the visualization can be viewed by clicking on the Data tab. The comma-separated-value input file can also be downloaded.


The source of data is listed in the Sources tab.


This visualization has been developed by the Open Water Foundation.

This visualization uses a template based on the Open Water Foundation variant of the "Gapminder" tool.

Source data for the visualization was downloaded from the CDSS SNODAS Tools data and further processed using TSTool software.