Observations QC Documentation

Quality control tests for meteorological observations were modeled after Shafer et al. (2000) J. of Atmos. and Oceanic Tech, which describes automated QC proceedures used for the Oklahoma Mesonet. Tests analyze each observation in both time and space.

Range Check

A simple gross error check to make sure the observation is within a reasonable range.

Ranges, by variable:
Variable Minimum threshold Maximum threshold
Temperature (including max, min)[K] 225 323
Relative Humidity [%] 0 105
Precipitation, 6-hr total [in.] 0.0 20.0
Precipitation, 24-hr total [in.] 0.0 40.0
Sea Level Pressure [hPa] 800 1050
Wind Speed [m/s] 0 60
Wind Gusts [m/s] 0 70
Wind Direction [deg.] 0 360

Step Check

This test looks for "spikes" in an station's time series for a given variable. Successive observations are compared and if the delta between them is above a set threhold, the value is flagged.

Step threholds, by variable:
Variable "Suspect" level step threshold "Warning" level step threshold
Temperature (including max, min)[K] 10 15
Relative Humidity [%] 60 80
Precipitation, 6-hr total [in.] N/A N/A
Precipitation, 24-hr total [in.] N/A N/A
Sea Level Pressure [hPa] 10.0 15.0
Wind Speed [m/s] 40.0 50.0
Wind Gusts [m/s] 40.0 50.0
Wind Direction [deg.] 360.0 360.0

An example of a temperature observation that fails the step test:

Persistence Check

This test looks at the standard deviation of 24 hours of data for each station and variable. If the standard deviation is below a set minimum allowed value, all values in the 24 hour period are flagged at the "warning" level, depending on set thresholds. As an additional test of persistence, this test determines the largest difference between successive observations in the 24 hour period. If this delta is less than a set threhold, all observations within the 24 hour period are flagged with a "warning" flag.

Persistence delta threholds by variable:
Variable "Warning" level step threshold
Temperature (including max, min)[K] 0.1
Relative Humidity [%] 0.1
Precipitation, 6-hr total [in.] N/A
Precipitation, 24-hr total [in.] N/A
Sea Level Pressure [hPa] 0.1
Wind Speed [m/s] 0.0
Wind Gusts [m/s] 0.0
Wind Direction [deg.] 0.1

An example of a wind speed observation that fails the persistence test:

Spatial Check

This test compares each observation to those of surrounding stations. Differences are calculated using values from stations within a 100-km radius and vertical elevation band, and if all differences are greater than a set threshold, the value in question is flagged. At least 5 stations must be found for the test to occur. If less than 5 stations are found with 100-km and within the set elevation band, a 150-km radius is used. For the larger radius, the differences threshold is eased.

Below are variable-specific parameters for the spatial test:
Variable Elevation Band (m, +/- this value) Lower Threshold Higher Threshold
Temperature (including max, min)[deg F] 150 10.0 15.0
Relative Humidity [%] 250 75 85
Precipitation, 6-hr total [in.] 500 3.0 4.0
Precipitation, 24-hr total [in.] 500 6.0 8.0
Sea Level Pressure [hPa] 1000 7.5 10.0
Wind Speed [knots] 250.0 15.0 20.0

An example of a temperature observation that fails the spatial test: