Definition of Current Conditions
This page outlines the criteria and definitions used for calculating and displaying statistics for the current conditions map layer.
Definition of Percentile
A percentile is a statistical measure that indicates the value below which a given percentage of data (or observations) in a group of data falls.
For example, on the map of streamflow current conditions, a river discharge at the 20th percentile indicates the value below which 20% of the data falls.
A streamflow which is greater than the 75th percentile is considered above normal.
A streamflow which is between 25th and 75th percentile is considered normal.
A streamflow which is less than the 25th percentile is considered below normal.
Criteria for Displaying Current Conditions
Zero Flow (Discharge) Station
A station reporting a flow (discharge) value of 0 m3/s is labeled "Not flowing", and no current condition will be available.
Daily Data Availability
A station must have at least 10 years of daily data for the current day, to calculate statistics, otherwise it is labeled "Not ranked due to lack of statistics", and no current condition will be available.
Discharge Unit Value Data Availability
Only stations reporting flow (discharge) data will have current conditions displayed.
A station with no discharge unit value data available for the current day is labeled "No discharge data available today", and no current condition will be available.
Statistical Calculation Methodology
The percentile calculations for current conditions follow the methodology outlined by the National Institute of Standards and Technology (NIST).
For detailed formulas and procedures, please refer to the NIST web page:
https://www.itl.nist.gov/div898/software/dataplot/refman2/auxillar/percenti.htm
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