QCMS Summary Message Description

The QCMS collects statistics on observational errors encountered for NWS sea-level pressure, potential temperature, dewpoint, surface wind, and as of OB4, altimeter setting. The system provides the total number of observations for each variable, the number of observations that failed the QC checks, the station names for the failed observations, and the error and threshold values for each of the failed observations. The error is defined as the difference between the QC analysis value and the observed value, as computed in the QCMS spatial consistency check.

Statistics are calculated for all stations in the 48 contiguous states and neighboring areas of Canada and Mexico. Stations from different networks are kept statistically separate. Specifically, for the initial implementation of the QCMS, the following stratifications are maintained: "ASOS," "OTHER-MTR," (non-ASOS METARs), "MARITIME," and prior to OB4, "NPN" (NOAA Profiler Network). Local mesonets are stratified by provider. For example, "CODOT," for the Colorado Department of Transportation. The statistics are available in the form of hourly QC messages. Figure 1 shows the CODOT hourly message for 16 September 1997 at 1300 UTC.


            CODOT HOURLY QUALITY CONTROL MESSAGE  (PAGE 1 OF 1)         

  **********************************************************************
  * 16-SEP-1997 *   SLP    * POT TEMP *  DEW PNT *    DD    *    FF    *
  *  1300 UTC   *   (MB)   * (DEG F)  *  (DEG F) *   (DEG)  *  (KNTS)  *
  **********************************************************************
  * TOTAL OBS   *      0   *     24   *     24   *     24   *     24   *
  *   QST OBS   *      0   *      0   *      1   *      1   *      1   *
  * PERCENT QST *   0.00   *   0.00   *   4.17   *   4.17   *   4.17   *
  **********************************************************************
  *    1-13     *          *          *  11(   7)*   -70    *    -5    *
  *             *          *          *          *          *          *
  *             *          *          *          *          *          *
  *             *          *          *          *          *          *
  *             *          *          *          *          *          *
  *             *          *          *          *          *          *
  *             *          *          *          *          *          *
  *             *          *          *          *          *          *
  *             *          *          *          *          *          *
  **********************************************************************
  ERROR = ANALYSIS - OBSERVATION            OB ERROR ( ERROR THRESHOLD )

Figure 1.Hourly QC message for Colorado Department of Transportation stations on 16 September 1997 at 1300 UTC. The station listed was found bad by the spatial consistency check.

Statistics for the total number of observations ("TOTAL OBS"), the total number of observations that failed the QC checks ("QST OBS"), and the percentage of failed observations ("PERCENT QST") are given at the top of each page of the hourly message. "QST" represents "questionable" observations. Errors and threshold values for the failed observations are listed in the columns. In ASOS hourly messages, the stations are also stratified by NWS region. Note that threshold values are not given for the surface wind errors in Figure 1. Wind observations are tested by computing observation errors and threshold values for each of the u and v components of the wind. However, observation errors are converted to polar coordinates before display in the QC messages. If either of the u or v components fail, both direction and speed errors are computed.

Stations listed in the QC messages are either in error due to hardware or software failure, or are unrepresentative of the observation scale and, as such, are susceptible to diurnal, mesoscale, and terrain effects. To help distinguish between the two, daily, weekly, and monthly (4-week) summaries of the hourly QC messages are also provided. The summaries include the percentage of failed observations and the average error and rms error for individual stations and for all stations combined. Figure 2 shows the daily NOAA Profiler Network (NPN) QC message for 16 May 1997.


          NPN   DAILY QUALITY CONTROL MESSAGE (PAGE   1 OF   1)                

  **********************************************************************
  *16-MAY-1997*   SLP    * POT TEMP *  DEW PNT *     DD     *    FF    *
  * 00-23 UTC *   (MB)   * (DEG F)  *  (DEG F) *    (DEG)   *  (KNTS)  *
  **********************************************************************
  * TOTAL OBS *    336   *    336   *    301   *     336    *    336   *
  *  QST OBS  *      0   *      0   *     11   *       0    *      0   *
  *PERCENT QST*   0.00   *   0.00   *   3.65   *    0.00    *   0.00   *
  **********************************************************************
  *    PRCO2  *          *          *21/-20/ 85*            *          *
  *           *          *          *          *            *          *
  *           *          *          *          *            *          *
  *           *          *          *          *            *          *
  *           *          *          *          *            *          *
  *           *          *          *          *            *          *
  *           *          *          *          *            *          *
  *           *          *          *          *            *          *
  *           *          *          *          *            *          *
  **********************************************************************
  ERROR= ANALYSIS-OBSERVATION           RMS ERROR/MEAN ERROR/PERCENT QST

Figure 2.Daily QC message for NOAA Profiler Network (NPN) surface stations on 16 May 1997.

As with the hourly messages, all stations in the domain are used to calculate the statistics reported at the top of each page, but only stations that have failed the QC checks (at least once in the reporting period) are listed in the individual statistics. Stations with large percentages of failed observations are most likely experiencing hardware or software failures. For example, the QC message in Figure 2 shows PRCO2 (Purcell, OK) as reporting bad dewpoint temperature observations 85% of the time. The rms errors for the station are also identical to the absolute value of the mean error, an indication that a persistent bias exists in the observations. The fact that the error is negative further indicates that the observations are biased high. With the information, the Profiler Control Center in Boulder was able to determine that the surface dewpoint sensor at Purcell had failed. The sensor has since been fixed, and the percentage of dewpoint observations failing the QC checks is back to zero.

Daily, weekly, and monthly summaries include only those stations with observations that have failed more than 25% of the time. This explains why Figure 3, which shows an OB4-formatted weekly message for the Oklahoma Mesonet, has no entries, as no stations had variables during this week that failed the QC more than 25% of the time.


          OK-Meso  WEEKLY QUALITY CONTROL MESSAGE (PAGE   1 OF   1)             

  *********************************************************************************
  *12-FEB-2004*   SLP    * POT TEMP *  DEW PNT *     DD     *    FF    *    ALT   *
  *18-FEB-2004*   (MB)   * (DEG F)  *  (DEG F) *    (DEG)   *  (KNTS)  *   (MB)   *
  *********************************************************************************
  * TOTAL OBS *      0   *  18342   *  18067   *   18829    *  18829   *  18497   *
  *  QST OBS  *      0   *     96   *     42   *      40    *     40   *      8   *
  *PERCENT QST*   0.00   *   0.52   *   0.23   *    0.21    *   0.21   *   0.04   *
  *********************************************************************************
  *           *          *          *          *            *          *          *
  *           *          *          *          *            *          *          *
  *           *          *          *          *            *          *          *
  *           *          *          *          *            *          *          *
  *           *          *          *          *            *          *          *
  *           *          *          *          *            *          *          *
  *           *          *          *          *            *          *          *
  *           *          *          *          *            *          *          *
  *           *          *          *          *            *          *          *
  *********************************************************************************
  ERROR= ANALYSIS-OBSERVATION           RMS ERROR/MEAN ERROR/PERCENT QST

Figure 3.Weekly QC message for Oklahoma Mesonet surface stations covering the week of 12-18 February 2004.


Last updated 24 February 2004.
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