QC FLAGS

Mesowest Data Flagging

*QFLAG* *VALUE*	*Meaning*
-1	Suspect: one or more of the variables from this location were outside the acceptable ranges
0	Unknown: flagging algorithms have not been applied to this data
1	Caution : pressure, temperature, humidity, and/or dew point data from this location should be used with caution.
2	OK: Data from this location has passed all defined qc checks.
9	Missing: QC checks beyond the max/min checks were not applied.

Included with the MesoWest data is a variable called QFLAG which is a function of time. This variable is used to define the quality of data from a station.

The initial QFLAG value for all observations is 0 or unknown, and is changed after processed by quality control algorithms.
The first part of the quality control process determines whether the variables reported from a station are of reasonable values. If one or more of the variables are out of range at a given time the QFLAG value is set to -1 and is considered a suspect observation. Also, if the difference bewteen the wind speed and wind gust is greater to or equal to 75 knots the data will be flagged as bad.
The next step in the quality control process uses a statistical regression analysis to provide additional quality information for temperature, pressure, and/or dew point data. The absolute average difference between the data and the regression estimates of the variables over a 6 hour period are used to flag the data as caution. Data are flagged quesetionable, QFLAG = 1, if the average temperature difference is greater than 10 degress F, the average pressure difference is greater than 10 mb, and/or the average dew point difference is greater than 15 degrees F. Also, if the difference between the wind speed and wind gust at a site exceeds 50 knots the data will be flagged as "caution".
Data that is not flagged by either the range limit checks or by the regression analysis checks are labeled as OK, QFLAG = 2. If a site did not report any temperature, pressure, or dew point data during the lastest 6 hour period then QFLAG = 9.
A QFLAG value of -1 is not overwritten by the other QC checks. All networks are currently being run through this quality control scheme except for the NWS or AFOS data which always have a value of 0 or unknown. The checking of bad data is done during the current processing cycle, however the regression analysis is performed on the previous processing cycle data set which is usually about 15 minutes old.