MET.TR.220 Aerodrome forecasts

(a)Aerodrome forecasts and amendments thereto shall be issued as a TAF and shall include, in the order indicated, the:

(1)identification of the type of forecast;

(2)location indicator;

(3)time of issue of forecast;

(4)identification of a missing forecast, when applicable;

(5)date and period of validity of forecast;

(6)identification of a cancelled forecast, when applicable;

(7)surface wind;

(8)visibility;

(9)weather;

(10)cloud;

(11)expected significant changes to one or more of these elements during the period of validity.

(b)TAF shall be issued in accordance with the template shown in Appendix 3.

(c)The period of validity of a routine TAF shall be either 9 or 24 or 30 hours, unless otherwise prescribed by the competent authority taking into account the traffic requirements for aerodromes which operate for less than 9 hours.

(d)TAF shall be filed for transmission not earlier than 1 hour before the commencement of their period of validity.

(e)The meteorological elements included in TAF shall be:

(1)Surface wind

(i)In forecasting surface wind, the expected prevailing direction shall be given.

(ii)When it is not possible to forecast a prevailing surface wind direction due to its expected variability, the forecasted wind direction shall be indicated as variable using ‘VRB’.

(iii)When the wind is forecasted to be less than 1 kt, the forecasted wind speed shall be indicated as calm.

(iv)When the forecast maximum speed exceeds the forecasted mean wind speed by 10 kt or more, the forecasted maximum wind speed shall be indicated.

(v)When a wind speed of 100 kt or more is forecasted, it shall be indicated to be more than 99 kt.

(2)Visibility

(i)When the visibility is forecasted to be less than 800 m, it shall be expressed in steps of 50 m; when it is forecasted to be 800 m or more, but less than 5 km, in steps of 100 m; when it is forecasted to be 5 km or more, but less than 10 km, in kilometre steps; and when it is forecasted to be 10 km or more, it shall be expressed as 10 km, except when conditions of CAVOK are forecasted to apply. The prevailing visibility shall be forecasted.

(ii)When visibility is forecasted to vary in different directions and the prevailing visibility cannot be forecasted, the lowest forecasted visibility shall be given.

(3)Weather phenomena

(i)One or more, up to a maximum of three, of the following weather phenomena or combinations thereof, together with their characteristics and, where appropriate, intensity, shall be forecasted if they are expected to occur at the aerodrome:

(A)freezing precipitation;

(B)freezing fog;

(C)moderate or heavy precipitation (including showers thereof);

(D)low drifting dust, sand or snow;

(E)blowing dust, sand or snow;

(F)dust storm;

(G)sandstorm;

(H)thunderstorm (with or without precipitation);

(I)squall;

(J)funnel cloud (tornado or waterspout);

(K)other weather phenomena, as agreed by the aerodrome meteorological office with the ATS units and operators concerned.

(ii)The expected end of occurrence of those phenomena shall be indicated by the abbreviation ‘NSW’.

(4)Cloud

(i)The cloud amount shall be forecast using the abbreviations ‘FEW’, ‘SCT’, ‘BKN’ or ‘OVC’, as necessary. When it is expected that the sky will remain or become obscured and clouds cannot be forecasted and information on vertical visibility is available at the aerodrome, the vertical visibility shall be forecasted in the form ‘VV’ followed by the forecasted value of the vertical visibility.

(ii)When several layers or masses of cloud are forecasted, their amount and height of base shall be included in the following order:

(A)the lowest layer or mass regardless of amount, to be forecasted as FEW, SCT, BKN or OVC as appropriate;

(B)the next layer or mass covering more than 2/8, to be forecast as SCT, BKN or OVC as appropriate;

(C)the next higher layer or mass covering more than 4/8, to be forecast as BKN or OVC as appropriate;

(D)cumulonimbus clouds and/or towering cumulus clouds, whenever forecasted and not already included under points (A) to (C).

(iii)Cloud information shall be limited to cloud of operational significance; when no cloud of operational significance is forecasted and ‘CAVOK’ is not appropriate, the abbreviation ‘NSC’ shall be used.

(f)Use of change groups

(1)The criteria used for the inclusion of change groups in TAF or for the amendment of TAF shall be based on any of the following weather phenomena, or combinations thereof, being forecasted to begin or end or change in intensity:

(i)freezing fog;

(ii)freezing precipitation;

(iii)moderate or heavy precipitation (including showers thereof);

(iv)thunderstorm;

(v)dust storm;

(vi)sandstorm.

(2)When a change in any of the elements given in point (a) is required to be indicated, the change indicators ‘BECMG’ or ‘TEMPO’ shall be used followed by the time period during which the change is expected to occur. The time period shall be indicated as the beginning and end of the period in whole hours UTC. Only those elements for which a significant change is expected shall be included following a change indicator. However, in the case of significant changes in respect of cloud, all cloud groups, including layers or masses not expected to change, shall be indicated.

(3)The change indicator ‘BECMG’ and the associated time group shall be used to describe changes where the meteorological conditions are expected to reach or pass through specified threshold values at a regular or irregular rate and at an unspecified time during the time period. The time period shall not exceed 4 hours.

(4)The change indicator ‘TEMPO’ and the associated time group shall be used to describe expected frequent or infrequent temporary fluctuations in the meteorological conditions which reach or pass specified threshold values and last for a period of less than 1 hour in each instance and, in the aggregate, cover less than one half of the forecast period during which the fluctuations are expected to occur. If the temporary fluctuation is expected to last 1 hour or longer, the change group ‘BECMG’ shall be used in accordance with point (3), or the validity period should be subdivided in accordance with point (5).

(5)Where one set of prevailing weather conditions is expected to change significantly and more or less completely to a different set of conditions, the period of validity shall be subdivided into self-contained periods using the abbreviation ‘FM’ followed immediately by a six-figure time group in days, hours and minutes UTC indicating the time the change is expected to occur. The subdivided period following the abbreviation ‘FM’ shall be self-contained and all forecasted conditions given before the abbreviation shall be superseded by those following the abbreviation.

(g)The probability of occurrence of an alternative value of a forecast element or elements shall be included when:

(1)a 30 % or 40 % probability of alternative meteorological conditions exists during a specific forecast time period; or

(2)a 30 % or 40 % probability of temporary fluctuations in meteorological conditions exists during a specific forecast time period. This shall be indicated in the TAF by using the abbreviation ‘PROB’ followed by the probability in tens of per cent and, in the case referred to in point (1), the time period during which the values are expected to apply, or in the case referred to in point (2), by using the abbreviation ‘PROB’ followed by the probability in tens of per cent, the change indicator ‘TEMPO’ and associated time group.