The SNODAS Tools page provides ways to access AOI-level SNODAS and stream flow data.
The data hosted on this page come from two major sources: NOHRSC SNODAS and USGS stream flow. The SNODAS data are delivered to a PSU ftp server daily. A script on the PSU server converts the delivered data to GIS raster format and extracts the aggregated AOI values to the server's database. The conversion and data extraction are also performed daily.
SNODAS Variables:
* To convert integers in files to model output values, divide integers in files by scale factor.
Monthly stream flow data:
The USGS adjusted stream flow data are downloaded to eBAGIS server automatically every 5th of the month from USDA Enterprise Content Management (ECM) stream flow json files which are updated a couple times a day for recent months (around 6 months). USDA adjusts the observed flow to remove the flow volume altered by man-made structures (e.g., dams), so that the stream flow data represent the "natural" flow. Some of the adjustment might take up to 6 months. The unit of monthly stream flow values is in acre-foot.
There are three query types of SNODAS data.
Query by date range for single AOI: Users specify the starting and ending dates to retrieve the daily SNODAS data for all eight variables.
Query by date of the year for single AOI: Users specify the day of the year and the year range to retrieve the data of the eight SNODAS variables for the given day of the year for all years specified in the year range.
Query SNODAS and streamflow correlation for all AOIs: Users specify one of the eight SNODAS variables and month(s) of monthly stream flow data to get the coefficients and r-square values of the regression models for all AOIs in the database.
All queries create .csv files that are automatically downloaded to users' computer hard disk. The .csv files have the following column headings.
Query by date range: date (mm/dd/yyyy), swe, depth, runoff, sublimation, sublimation_blowing, precip_solid, precip_liquid, average_temp
Query by date of the year: date (mm/dd/yyyy), swe, depth, runoff, sublimation, sublimation_blowing, precip_solid, precip_liquid, average_temp
Query SNODAS and streamflow regression: awdb_id, name, intercept, slope, r2, std_err_res, variable, query_day, query_month, start_month, end_month, start_year, end_year, num_years_included, streamflow_yyy1, streamflow_yyy2, streamflow_yyy3, ...snodas_yyy1, snodas_yyy2, snodas_yyy3, ...
Whereas:
awdb_id: NRCS awdb forecast station triplet ID (e.g., "10336715:NV:USGS")
name: NRCS awdb forecast station name (e.g., "Marlette Lake Inflow")
intercept: the intercept (b) of the linear regression model of monthly (or multiple-monthly) stream flow (y) and daily SNODAS variable (x), where y = ax + b.
slope: the slope (a) of the linear regression model of monthly (or multiple-monthly) stream flow (y) and daily SNODAS variable (x), where y = ax + b.
r2: the r-squared value of the regression model with a value between 0 and 1. Larger r-squared values indicate a better fit of the data to the regression line.
std_err_res: standard error of the residuals in stream flow unit (acre-foot).
variable: a text indicating which of the 8 daily SNODAS variables was used in the model. The valid values are: "swe", "depth", "runoff", "sublimation", "sublimation_blowing", "precip_solid", "precip_liquid", and "average_temp".
query_day: the day of the targeted forecast date
query_month: the month of the targeted forecast date
start_month: the beginning month of the monthly stream flow data
end_month: the ending month of the monthly stream flow data
start_year: the beginning year of the data used in the regression model
end_year: the ending year of the data used in the regression model
num_years_included: the number of years of data used in the regression model
streamflow_yyy1: the stream flow value from the first year of start_year
streamflow_yyy2: the stream flow value from the second year of start_year
streamflow_yyy3: the stream flow value from the third year of start_year
...
snodas_yyy1: the SNODAS variable value from the first year of start_year
snodas_yyy2: the SNODAS variable value from the second year of start_year
snodas_yyy3: the SNODAS variable value from the third year of start_year
...