GEN 3.5.1   Responsible service

The meteorological services for civil aviation are provided by Croatia Control Ltd., Aeronautical Meteorology Service (MET).

The service is provided in accordance with CIR (EU) 2017/373, as amended and complemented, and with the provisions contained in the following ICAO documents:

• Annex 3 - Meteorological Service for International Air Navigation;
• Doc 7030 - Regional Supplementary Procedures;
• Doc 7754 - Air Navigation Plan - European Region;
• Doc 8400 - Abbreviations and Codes;
• Doc 8896 - Manual of Aeronautical meteorological Practice.

Differences to these provisions are detailed in subsection GEN 1.7.

GEN 3.5.2   Area of responsibility

Area meteorological watch is provided for the Zagreb FIR.

GEN 3.5.3   Meteorological observations and reports

Meteorological observations and reports are provided and disseminated from aeronautical meteorological stations, according to ICAO Annex 3 regulations. Routine reports are issued at HR+00 and HR+30.

Observations are provided at airports ZAGREB/Franjo Tuđman, SPLIT/Saint Jerome, PULA, DUBROVNIK/Rudjer Boskovic, ZADAR/Zemunik, OSIJEK/Klisa, RIJEKA/Krk I., LOŠINJ/Lošinj I. and BRAČ/Brač I.

Runway visual range (RVR) assessment is made at airport ZAGREB/Franjo Tuđman, PULA, SPLIT/Saint Jerome, DUBROVNIK/Rudjer Boskovic, ZADAR/Zemunik and OSIJEK/Klisa. The RVR values are displayed automatically in digital form at the MET and ATS units.

AUTO METAR is made from sensor data and a calculation of algorithms. Sensors are located on sites representative for airport measurements. In AUTO METAR reports weather conditions are reported in accordance with ICAO Annex 3 if they are within the detection range of the system.

There is no difference between METAR and AUTO METAR reports for the following elements:

• Wind speed and direction
• Temperature and dew point
• Pressure (QNH)
• RVR

Differences and limitations of AUTO METAR reports in relation to METAR reports are reflected in the following elements:

• Visibility
• Present Weather
• Cloudiness
• Supplementary information on recent weather phenomena
  
  

VISIBILITY:

In AUTO METAR reports aeronautical visibility is determined and reported as defined by ICAO Annex 3 at the location of the visibilimeter. Visibility cannot be estimated within 360 DEG and this is why the reported visibility may not represent prevailing values. Minimum visibility in a certain direction cannot be reported.

PRESENT WEATHER:

In AUTO METAR reports present weather and recent weather information is assessed from the sensor located at the visibilimeter position. Sensor limitations are single point measurement (covering only one runway threshold) and the inability of reporting certain phenomena (GR, GS, PRFG, DU, SA, FU). Also, it is possible that the sensor reports present weather differently from the one that is actually present. Apart from the phenomena itself, the difference is more to be expected in the characteristic or the intensity which is due to a limitation of the sensor and a result of a single point measurement. The most frequent observed error is in reporting feeble rain (-RA) when there is no precipitation.

The lightning detection network is reliable in reporting TS and VCTS. In case of using a backup sensor rare occurrences of lightning that was not detected by the system are possible.
According to ICAO Annex 3 showers (SH) are not reported due to a lack of algorithm.

CLOUDS:

In AUTO METAR reports cloud amount and ceiling is reported as a result of ceilometer measurements and an algorithm calculation. The laser-based measuring principle in one point prevents reporting cloud cover that is not, or recently has not been above the sensor itself. Determination of cloud amount is made by an algorithm that includes cloud detection data from the recent period. The algorithm works well for homogenous cloud distribution and moving clouds. Clouds off the sensors cannot be detected. Orographic clouds are most likely not to be detected by the system.
TCU and CB clouds are not reported in AUTO METAR reports due to a lack of algorithm.

MONITORING AND TECHNICAL SUPPORT:

The system for the production and distribution of AUTO METAR is monitored by the technical service. Technical failure of an individual sensor can be replaced by another sensor only when there are other redundant sensors/indicators
. Otherwise, missing data is replaced by slashes as usual in AUTO reports.