2   Observing Systems and Operating Procedures

At all aerodromes automated weather observing systems (AWOS) are installed. Human meteorological observations (visibility, cloud type and/or amount, some of present weather phenomenon and supplementary information) are made additionally to automated observations. Appropriate ATS units, briefing and aerodrome offices have a real time weather displays with all data measured by AWOS including data inserted manually by human observers. At EYVI, EYKA and EYPA all displayed data are updated in 10 s intervals. At EYSA displayed data values on the monitors are updated when particular data values are measured by AWOS.

Surface wind. Surface wind speed and direction are measured by cup anemometers and wind vanes or ultrasonic sensors located at both ends of the runway near THR at a height of 10 M above the ground surface.

EYKA wind sensors are the cup anemometers, EYVI, EYPA, EYSA wind sensors – the ultrasonic. The unit knot (KT) is used to indicate surface wind speed. 10 minutes average of the true wind direction and wind speed, variation in wind direction (consisting of the two extreme directions between which the wind has varied during the past 10 minutes) and variation from the mean wind speed (gust) during the past 10 minutes are reported in METAR. The wind data from the wind sensor representing TDZ zone of the current RWY in use is always included in a current reports. The magnetic wind direction and speed (2-minute average), variation in wind direction and variations from the mean wind speed (gusts) (during the past 10-minutes) are reported in local reports and transmitted to ATIS for broadcasts. On ATS unit’s real time weather displays all wind data, including crosswind and headwind/tailwind values, relating to the wind sensors installed near the runway, are displayed.

Visibility. Visibility is measured by transmissometers at a height of approximately 2.5 M above RWY or observed visually by human observer (if necessary) and reported in metres.

At all aerodromes reported visibility in METAR is a prevailing visibility (10-minute average median value) determined from all measuring sites. When the visibility is not the same in different directions and the lowest visibility is different from the prevailing visibility and

1. less than 1500 M or
2. less than 50% of the prevailing visibility and less than 5000 M,

the lowest visibility is also included in METAR (with or without indication of its general direction).

At EYKA and EYPA automatic METAR reports a visibility value (10-minute average) from the measuring site representative to TDZ of the current RWY in use is included.

At EYVI, EYKA and EYPA in local reports a visibility value (1-minute average) from the measuring site representative to TDZ of the current RWY in use is included. At EYSA in local reports a visibility values (1-minute average) from all measuring sites are included.

At all aerodromes on ATS unit’s real time weather displays visibility data (1-minute average) from all measuring sites representing all zones along the runway are displayed.

Runway Visual Range. Assessment of the runway visual range (RVR) is carried out by means of transmissometers.

The RVR assessments are performed using MOR values from transmissometers and information of background luminance and runway light intensity. The RVR is reported in meters throughout periods when the visibility or the RVR is less than 1500 M. The lower limit for RVR reporting is 50 M and 2000 M is the upper limit. The RV reported in METAR is RVR (10 minute average) assessed using MOR from measuring site representative to TDZ of the current RWY in use and using 100% runway light intensity.

The RVR reported in local reports at EYVI, EYKA, EYPA and EYSA is RVR (1 minute average) values assessed using MOR from all measuring sites representing all zones along the runway and using runway light intensity:

1. for a runway with the lights switched on, the light intensity actually in use on that runway; and
2. for a runway with lights switched off (or at the lowest setting pending the resumption of operations), the optimum light intensity that would be appropriate for operational use in the prevailing conditions.

The RVR reported in local reports at EYPA is RVR (1 minute average) values assessed using MOR from measuring sites representing both zones along the runway and using 100% runway light intensity.

On ATS unit’s real time weather displays RVR data (1-minute average) from all measuring sites representing all zones along the runway are displayed.

Present weather. The present weather phenomena are observed by means of a present weather sensors, integrated into transmissometers, lightning detector and additionally by the observer.

Present weather phenomena are reported in accordance with ICAO Annex 3 and Commission implementing regulation (EU) 2017/373 requirements.

Clouds. Laser ceilometers are used at all aerodromes to determine the height of cloud base and cloud amount or vertical visibility in case when the sky is obscured and cloud base is not detected.

They are installed at ILS MM at the both ends of the RWY. The height of cloud base or vertical visibility is reported in feet above the aerodrome elevation. In METAR and SPECIAL reports the height of cloud base is reported in steps of 100 feet up to 10000 feet. The ICAO recommended algorithm is used for cloud base and amount calculations.

In local reports at EYVI, EYKA and EYPA to report the height of cloud base steps of 50 FT up to and including 300 FT and steps of 100 FT between 300 FT and 10 000 FT are applicable, and the vertical visibility - steps of 50 FT up to and including 300 FT and steps of 100 FT between 300 FT and 2 000 FT. In local reports at EYSA to report the height of cloud base steps of 100 FT up to 10 000 FT are applicable, and the vertical visibility – steps of 100 FT up to 2000 FT. Only cloud of operational significance (a cloud with the height of cloud base below 5000 feet or a cumulonimbus cloud or a towering cumulus cloud at any height) is included in local reports. Type of cloud, if applicable, is inserted to reports (except fully automatic reports) by a human observer. In automatic reports at EYKA and EYPA type of clouds is indicated as not available by the use of code ///. In automatic reports at EYSA type of clouds are not indicated as not available.

On ATS unit’s real time weather displays the data on the height of cloud base, amount and type of clouds are displayed. At EYVI ATS weather displays instant measured data (in 30 s intervals) on cloud height is displayed additionally.

Air temperature and dew point temperature. Air temperature and air humidity (from which the dew point temperature is calculated) at EYKA are measured by sensors placed in a solar radiation protection 2 M above the ground in the meteorological garden, at EYVI, EYPA, EYSA – on the masts of wind sensors at the both ends of the RWY. All measured values are updated in 60-second intervals. On ATS unit’s real time weather displays the data on the air and dew point temperature are displayed.

Atmospheric pressure. Digital aviation barometers are used as main and backup sensors for QNH and QFE values calculations. All values are updated in 60-second intervals. The QNH value in steps of whole hectopascal is included in all reports. On ATS unit’s real time weather displays QNH and QFE values in hPa are displayed. At EYVI, EYKA and EYPA ATS weather displays QNH and QFE values in Hg and mmHg units are displayed additionally. At EYSA ATS weather displays QNH and QFE values in mmHg units are displayed additionally.

Supplementary information. In METAR and SPECIAL reports information on wind shear, based on aircraft reports. In local reports (except automatic reports) information on wind shear along the take-off path or approach path and other supplementary information received from aircrafts via ATS units (including severe and moderate turbulence or icing) is included by a human observer.

RWY surface temperature, water film height and freezing points are measured by the road sensors at EYSA at both ends of the RWY.

1   MET information for pre-flight planning

Crew members and/or other flight-related staff at EYVI, EYKA, EYPA and EYSA are consulted by phone by Forecast and Warnings Division (aviation). Flight documents are provided to international and, if necessary, to local flights.

Flight documents include: a charts of significant meteorological phenomena, a charts of upper wind and upper air temperatures and the latest available METAR/SPECI reports and TAF forecasts of the departure, destination and alternate aerodromes; the latest valid SIGMET information along the flight route and AIRMET information for low level flights.

At the request of EYVI, EYKA, EYPA, EYSA tThe required flight documents arecan be sent by fax or e-mail from Forecast and Warnings Division (aviation).

2   MET information for general aviation

Forecasts for general aviation (IFR and VFR) for low-level flights are prepared in a SIGWX charts format and cover information for traffic below FL100 within the Vilnius FIR and further into Europe.

SIGWX forecasts for low-level flights are prepared every 6 hours at daytime and are transmitted not later than 1 hour prior to the beginning of their validity period. SIGWX charts are issued at 0200 UTC for fixed forecast time of 0600 UTC, at 0800 UTC for fixed forecast time of 1200 UTC and at 1400 UTC for fixed time of 1800 UTC. Charts cover the period of validity from 3 hour before to 3 hour after the fixed time. The charts show the position, direction and speed of movement of surface fronts, pressure centers and boundaries of significant weather zones for the fixed time, height of zero-degree isotherm. Height indications in SIGWX forecasts are given in hectofeet above ground level (AGL). If necessary, AIRMET information is issued and amendments of SIGWX charts for low-level flights are prepared (AMD and COR).

SIGWX forecasts for low-level flights are disseminated according to agreements with users and are available at all Lithuanian aerodromes

3   Other meteorological information

The weather satellite picture covering EUR region is provided and displayed at the pre-flight briefing office in Vilnius. Information obtained from two ground based meteorological radars (Doppler type) installed at Laukuva (West part of Lithuania) and Traku Voke (not far from Vilnius aerodrome) is also available for pilots at pre-flight briefing office in Vilnius.

Air-sport users (gliders, hot air balloon pilots) if require some specific types of meteorological information, shall apply to LHMS and agree on the terms of providing required information.

1   Meteorological Watch Office

The Forecast and Warnings Division (aviation) performs the functions of the Meteorological Watch Office (MWO).

The Forecast and Warnings Division (aviation) prepare SIGMET information for Vilnius FIR on the following present and forecasted significant meteorological phenomena:

1. thunderstorm:
   • obscured,
   • embedded,
   • frequent,
   • line squall,
   • obscured with heavy hail,
   • embedded with heavy hail,
   • frequent with heavy hail,
   • line squall with heavy hail;
2. turbulence:
   • severe turbulence;
3. icing:
   • severe icing,
   • severe icing due to freezing rain;
4. volcanic ash clouds;
5. radioactive clouds.

The three-character number to be used in the sequence number should correspond to the number of SIGMET messages, dependent on the phenomena as indicated by the first character, issued for the FIR since 0001 UTC on the day concerned. The period of validity of SIGMET information is not more than 4 hours. In preparing SIGMET for volcanic ash clouds (VA SIGMET), the MWO Vilnius will use the relevant advisory information received from the Volcanic Ash Advisory Centers (VAAC) in London or Toulouse. The period of validity VA SIGMET messages for Vilnius FIR is extended up to 6 hours. The information is transmitted to international meteorological data banks.

The Forecast and Warnings Division (aviation) forwards its own and adjacent MWOs SIGMET information to ACC and ATC.

AIRMET information, prepared in abbreviated plain language (English), is issued for traffic operating below FL100, if present and/or forecasted weather phenomena (in accordance with para 2.14 of Appendix 6, Part II, ICAO Annex 3), which may affect the safety of low-level flights, have not been included SIGWX forecast chart.

AIRMET information is transmitted to international meteorological data bank and to ACC and ATC.

Wind shear reports from aircraft are included in METAR and SPECIAL reports (except automatic).

2   Warning Service

Aerodrome warnings for EYVI, EYKA, EYPA and EYSA aerodromes are prepared by the Forecast and Warnings Division (aviation). Warnings shall give information of meteorological conditions which can adversely affect the parked aircraft and the aerodrome facilities or impede RWY cleaning. Warnings are prepared if one or more of the following phenomena occurs or is expected to occur at the airport:

For EYVI, EYKA, EYPA:

• air temperature change from positive to negative value;
• freezing precipitation;
• heavy snowfall lasting longer than 2 hours;
• wind speed in the gusts 20 m/s or more;
• thunderstorm, 9 km radius around aerodrome.

For EYSA:

• freezing precipitation;
• wind speed 15 m/s or more.

Text of the aerodrome warnings is prepared in English language and numerical values and is distributed according to interoperability of services. The validity period of the aerodrome warning is not more than 4 hours.

Warnings about wind shear for EYVI aerodrome are based on aircraft reports, received via ATS, and are prepared in abbreviated plain language using approved ICAO Annex 3 and Commission implementing regulation (EU) 2017/373 abbreviations and numerical values and are distributed according to interoperability of services. The validity period of the wind shear warning is not more than 1 hour. Additionally information on wind shear, received from ATS, is included in METAR and/or SPECIAL reports.

Aerodrome and wind shear warnings are understood to cancel itself automatically at the end of its validity period. If the phenomenon persists a new warning will be issued with the next sequence number and for a further period of validity. The numbering of warnings starts every day at 0001 UTC separately for each aerodrome.