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QA and QC

The increased visibility of the NWS Hydrology program on the web, including near-real-time stream gage observations, requires more timely and persistent quality control to ensure bad values do not appear in the forecast or observed hydrographs on the web.

The WFO has primary responsibility for data quality. Ensure the quality of hydrologic products and services by completing two steps - quality assurance (QA) and quality control (QC).

Quality Assurance Quality Control

Quality Assurance (QA) programs are preventive activities to minimize or avoid data quality errors.

Corrective actions include:

  • Defining observer procedures and equipment siting standards.

  • Staff and observer training.

  • Station visitations and accurately documenting station metadata.

  • Internal data checking (QA algorithms).

QA Steps in the Dataflow
Hydrometeorological Automated Data System (HADS) uses parity checking, an error detection technique, to test the integrity of digital data.

The AWIPS SHEF Decoder  parses out data from ALERT and other automated gages with sensor or transmission errors. The data does not post to the database.

Monitor the "Rejected Data Trashcan” in HydroView to ensure the data is truly "bad" data and not an extreme event.

See the SHEF manual for details on data flags (Table 10) and SHEF error messages (Appendix J).

QC programs are corrective actions taken by NWS offices to ensure high quality data in real-time through post processing.

In most cases, the corrective action involves “fixing” the data, but it may include removing the suspect data or simply discounting the data in our decision-making process.

QC measures include monitoring:

  • ASOS data for timeliness, missing elements, false precipitation, and spatial consistency.
  • Cooperative Observer Program (COOP) reports for missing elements and data discrepancies.
  • Climate observations for data discrepancies, missing elements, and spatial consistency.

Coordinate with the RFC(s) after finding data errors (including those due to bad gages), issue corrected data in products, and notify the gage owner.

QAQC

Reference: NWS Directive 10-1305