3.5.3.2   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 at EYVI 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 (EYKA) and ultrasonic sensors (EYPA, EYVI and EYSA) located at both ends of the runway near THR at a height of 10 M above the ground surface.

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 1 500 M. The lower limit for RVR reporting is 50 M and 2 000 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.

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.

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. The height of cloud base is reported in steps of 100 FT up to 10 000 FT and the vertical visibility is reported in steps of 100 FT up to 2 000 FT. The ICAO recommended algorithm is used for cloud base and amount calculations.

In local routine and local special 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 2 000 FT. Only cloud of operational significance (a cloud with the height of cloud base below 5 000 FT 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 is 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 2 M above the ground on mast of the wind sensor RWY08, 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 (Celsius degrees).

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.

3.5.4.1   Forecasting services

Forecasting services for aerodromes in Lithuania are provided by the LHMS Forecasts and Warnings Division (aviation), which carries out the duties of AMO.

Aerodrome forecasts

Aerodrome forecasts are prepared in TAF code form. 24-hour validity period TAFs (0024, 0606, 1212, 1818) are issued every 6 hours for EYVI, EYKA and EYPA, 9-hour validity TAFs (0009, 0312, 0615, 0918, 1221, 1524, 1803) are prepared every 3 hours for EYSA. TAFs are disseminated no earlier than 1 hour before the commencement of their validity. If necessary, TAF amendments (COR/AMD) are issued. TAFs are disseminated to OPMET banks and SADIS.

Forecasts for landing

Forecasts for landing for EYVI are provided by LHMS Forecasts and Warning Division (aviation), for EYSA – Lithuanian Air Force Air Base Air Operations Group Air Operations Support Squadron Meteorological Section. Forecasts for landing are prepared in TREND code form. A TREND forecast contains a concise statement of the expected significant changes in the meteorological conditions (surface wind direction and speed and their variations, visibility, phenomena, and clouds) at that aerodrome and is appended to METAR/SPECIAL. The period of validity of a TREND is 2 hours from the time of the METAR/SPECIAL, which forms part of the landing forecast.

Forecasts for take-off

Forecasts for take-off from EYVI, EYKA, EYPA and EYSA are prepared on request and contain concise information about expected meteorological conditions (surface wind direction and speed and their variations, air temperature, and atmospheric pressure) over RWY. The period of validity of the forecast for take-off is 2 hours.

Forecasts for take-off from EYVI, EYKA, EYPA and EYSA can be obtained by contacting LHMS Forecasts and Warnings Division (aviation) by phone +370 648 05 448 or +370 648 06 768 at least 3 hours before the expected departure of the aircraft.

Atmospheric pressure forecasts

QNH forecasts contain concise information about expected minimal QNH values within each area of the Vilnius FIR. The distribution of areas is shown in Figure 1. QNH forecasts are issued every 6 hours for validity periods 0309, 0915, and1521 UTC and transmitted to ATS units not later than 1 hour before the commencement of their validity. QNH forecasts are continuously monitored, and amendments (AMD) are issued if necessary.

Area forecasts for low-level flights

Area forecasts for low-level flights are prepared as a significant weather prognostic SIGWX chart below FL100. The SIGWX chart contains information on meteorological information that may have an impact on low-level flights within Vilnius FIR and further into Europe. SIGWX chart is issued every 6 hours during daylight time at fixed forecast times of 06:00, 12:00, and 18:00 UTC not later than 1 hour before the commencement of their validity. The SIGWX chart covers the period of validity from 3 hours before to 3 hours after the fixed time. The graphical part of a SIGWX chart depicts the weather situation at the beginning of the validity period.

The SIGWX chart shows the position, direction, and speed of movement of atmospheric pressure centers and surface fronts, the boundaries of significant weather zones, and depicts information about:

• the following phenomena warranting the issuance of a SIGMET, and which are expected to affect low-level flights. More information about SIGMET services is provided in part GEN 3.5.8.
• widespread mean surface wind speeds above 30 KT;
• widespread surface visibility of less than 5000 m, including weather phenomena reducing visibility;
• clouds below FL100, including cloud amount, type, and height of the base and top
• TCU/CB clouds (ISOL TCU, OCNL TCU, FRQ TCU, ISOL CB, OCNL CB, FRQ CB);
• thunderstorm with and without hail (ISOL TS, OCNL TS, ISOL TSGR, OCNL TSGR);
• moderate or severe icing, not associated with convective clouds (MOD ICE/SEV ICE);
• moderate or severe turbulence, not associated with convective clouds (MOD TURB/SEV TURB);
• height of 0°C level below FL100;
• sea surface temperature;
• volcanic eruption;
• release of radioactive materials into the atmosphere.

The SIGWX charts are continuously monitored, and amendments (AMD) are issued if necessary. In addition, AIRMET for Vilnius FIR are issued as needed during the validity of SIGWX charts. More information about AIRMET services is provided in part GEN 3.5.8.

SIGWX forecasts are distributed according to agreements with users and can be obtained from self-briefings located at EYVI, EYKA, EYPA and EYSA and from the LHMS Forecasts and Warnings Division (aviation).

3.5.4.2   Warning services

Warning services for aerodromes in Lithuania are provided by the LHMS Forecasts and Warnings Division (aviation), which carries out the duties of AMO.

1. Aerodrome warnings contain a concise statement of meteorological information that can have a negative impact on parked and moored aircraft, aerodrome facilities, or impede RWY cleaning.

   Aerodrome warnings are issued if one or more of the following phenomena occurs or is expected to occur at the aerodrome:

   EYVI, EYKA, EYPA:

   • air temperature change from positive to negative (FROST);
   • freezing precipitation (FZDZ or FZRA);
   • heavy rain (HVY RA);
   • heavy snowfall lasting more than 2 hours(HVY SN);
   • strong surface wind exceeding 40 KT (SFC WSPD or SFC WIND);
   • thunderstorm 9 KM radius around aerodrome (TS).

   EYSA:

   • freezing precipitation;
   • strong surface wind exceeding 30 KT;
2. Wind shear warnings contain a concise statement of information about the reported or/and expected evidence of wind shear at Vilnius aerodrome. The preparation of a wind shear warning and a confirmation of the warning previously issued are mainly based on aircraft reports. Information about wind shear received from ATS units is included in METAR/SPECIAL.

Aerodrome warnings and wind shear warnings are prepared in abbreviated plain English using ICAO-approved abbreviations and numerical values and are distributed according to interoperability services. The validity period of an aerodrome warning is no more than 4 hours, and the validity period of a wind shear warning is no more than 1 hour. Aerodrome warnings and/or wind shear warnings will be cancelled when a phenomenon is no longer occurring or is no longer expected to occur at the aerodrome. The warning is understood to automatically cancel itself 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 aerodrome warnings starts every day at 00:01 UTC and is separate for each aerodrome.

3.5.4.3   MET information for pre-flight planning

Flight documentation

Flight documentation for international and domestic flights for operators and flight crew members is prepared by the LHMS Forecasts and Warnings Division (aviation). Flight documentation comprises:

• a significant weather prognostic chart (SWM, SWH);
• upper winds and air temperature prognostic charts;
• METAR/SPECIAL, including TREND, for the aerodromes for departure, intended landing, and destination alternate aerodromes;
• aerodrome forecasts (TAF) and their amendments for the aerodromes for departure, intended landing, and destination alternate aerodromes;
• SIGMET, AIRMET, information about volcanic ash, tropical cyclones, and space weather for all en route;
• area forecast for low-level flights (SWL), if appropriate.

Flight documentation is transmitted by email or fax from the LHMS Forecasts and Warnings Division (aviation).

Satellite and meteorological radar data is available at online self-briefings located at EYVI, EYKA, EYPA, and EYSA, as well as on the LHMS website via http://www.meteo.lt/lt/palydovu-informacija and http://www.meteo.lt/lt/radaru-informacija.

Briefings and consultations

Briefings and/or consultations for operators and flight crew members are provided by the LHMS Forecasts and Warnings Division (aviation) by phone +370 648 05 448 or +370 648 06 768.

Information about abbreviations used for flight documentation and types of consultations is provided in AD 2.11.

3.5.4.4   Other meteorological information

Specific types of meteorological information for gliders, hot air balloon pilots, etc. can be obtained by agreeing terms for the provision of the required information with LHMS.