Data Clarifications

Below you will find clarifications about some of the data that can be retrieved from Frost.

Standard time offsets

Some elements are historically measured and aggregated at specific times during the day. This is indicated by the timeOffset value. Sometimes multiple timeseries are available at the same station, with the only difference being the timeOffset value.

The table below is a guideline for what to choose when in doubt. The timeOffset values listed are the most typical values used at MET Norway's own stations.

For automatic filtering according to this table, see the concepts page

element_idtimeResolutionPreferred offsetWhy
max(air_temperature P1D)P1DPT18HStandard sampling period for temperature extremes is 19-18 UTC
max(air_temperature PT12H)PT12HPT6HThis offset indicates our standard timeseries, where the first calculation is performed at 06 UTC
min(air_temperature P1D)P1DPT18HStandard sampling period for temperature extremes is 19-18 UTC
min(air_temperature PT12H)PT12HPT6HThis offset indicates our standard timeseries, where the first calculation is performed at 06 UTC
snow_coverage_typeP1DPT6HStandard sampling time for snow observations is 06 UTC
sum(precipitation_amount P1D)P1DPT6HStandard sampling period for precipitation is 07-06 UTC
sum(precipitation_amount P1M)P1MPT6HStandard sampling period for precipitation is 07-06 UTC
surface_snow_thicknessP1DPT6HStandard sampling time for snow observations is 06 UTC
Other elementsOther resolutionsPT0HFor cases not listed above, PT0H is always the preferred offset when multiple offsets are returned.

Quality code

The data is run through a quality control system that can assign several different quality flags which mean different things. For further information see useinfo and controlinfo.

FROST tries to give the user a single value to represent the general quality of the observation. It is an aggregation of 2 of the flags given by the quality control system.

Below is the description of the two flags used:

useinfo[2] - quality level of the original value
  • 0 = original value found to be good
  • 1 = original value suspicious (likely correct)
  • 2 = original value suspicious (likely erroneous)
  • 3 = original value definitely erroneous
  • 9 = no quality information given
useinfo[3] - treatment of the original value
  • 0 = original value is kept unchanged
  • 1 = original value is manually or automatically corrected with a good result
  • 2 = original value is manually or automatically interpolated with a good result
  • 3 = original value is automatically corrected
  • 4 = original value is automatically interpolated
  • 5 = original value is manually created from accumulated values
  • 6 = original value is automatically created from accumulated values
  • 8 = original value is thrown out
  • 9 = quality information is not given

This is how FROST creates one value from them:

useinfo[2], useinfo[3] => FROST
  • anything, '1' => (1) // OK
  • anything, '2' => (1) // OK
  • anything, '3' => (6) // Very uncertain
  • anything, '4' => (6) // Very uncertain
  • anything, '5' => (1) // OK
  • anything, '6' => (1) // OK
  • '0', anything => (0) // OK
  • '9', anything => (2) // Uncertain
  • '1', '0' => (5) // Uncertain
  • '2', '0' => (5) // Uncertain
  • '3', '0' => (7) // Erroneous
  • '3', '8' => (7) // Erroneous
  • all other cases => None // Undefined

Performance and Exposure Categories

Exposure category is used to give information about the quality of the placement of a station. Performance category is used to give information about the quality of a sensor (which is located at a given station).

Exposure Category Description
1 Fulfils all WMO's demands on location
2 Unknown location, assumed good
4 Unknown location, assumed bad
5 Bad location
Performance Category Description
A The sensor type fulfills the requirements from WMO/CIMOs on measurement accuracy, calibration and maintenance.
B Rutines for calibration and maintanance are known. Control of the montage exists. The precision of the measurment is lower than the WMO/CIMO requirements.
C The sensor type is assumed to fulfill the WMO/CIMO requirements. Missing measurement for control, rutines for calibration, or maintanence.
D The sensor type is assumed to fulfill the WMO/CIMO requirements. Some controls show deviations from the WMO/CIMO requirements.
E Less valuable. Possibly useful for extraordinary purposes. Unknown performance

Explanations for some coded negative value elements

Some elements can use negative observation values that are coded to mean a certain thing - and are not an actual value for a measurement. Product time series also exist where these special values are converted to a measurement value. Below you will find a table with explanations of these values.

Observation value element ID Converted value Description
-3 wind_from_direction not converted No unique wind direction is given when winds are weak
-3 cloud_area_fraction not converted Cloud cover is not estimated because of fog or analogous phenomena
-3 low_type_cloud_area_fraction not converted Cloud cover is not estimated because of fog or analogous phenomena
-3 cloud_area_fraction1 not converted Cloud cover is not estimated because of fog or analogous phenomena
-3 cloud_base_height not converted Cloud height is not estimated because of fog or darkness
0 surface_snow_thickness not converted Snowdepth less than 0.5 cm
-1 surface_snow_thickness not converted Zero snowdepth or partial snow cover
-3 surface_snow_thickness not converted Not possible to measure snowdepth
-1 max(surface_snow_thickness P1M) not converted Zero snowdepth or partial snow cover
-1 min(surface_snow_thickness P1M) not converted Zero snowdepth or partial snow cover
-1 snow_coverage_type not converted No snow in station area
-1 min(snow_coverage_type P1M) not converted No snow in station area
-1 max(snow_coverage_type P1M) not converted No snow in station area
-1 state_of_ground not converted No snow or ice cover in the station area
-1 sum(precipitation_amount PT6H) not converted No precipitation
-1 sum(precipitation_amount PT12H) not converted No precipitation
-1 sum(precipitation_amount P1D) 0.0 mm No precipitation
-1 sum_over_undefined_period(precipitation_amount PT1H) not converted No precipitation
-1 max(sum(precipitation_amount P1D) P1M) 0.0 mm No precipitation
-1 sum(precipitation_amount P30D) 0.0 mm No precipitation
-1 sum_until_day_of_year(precipitation_amount P1D) 0.0 mm No precipitation

Explanation of the lightning data format

Lightning data is in UALF format: