NCO.OP.160 Meteorological conditions

APPLICATION OF AERODROME FORECASTS (TAF & TREND) Where a terminal area forecast (TAF) or meteorological aerodrome or aeronautical report (METAR) with landing forecast (TREND) is used as forecast, the following criteria should be used:

(a)From the start of a TAF validity period up to the time of applicability of the first subsequent 'FM...' or 'BECMG' or, if no 'FM' or ‘BECMG' is given, up to the end of the validity period of the TAF, the prevailing weather conditions forecast in the initial part of the TAF should be applied.

(b)From the time of observation of a METAR up to the time of applicability of the first subsequent 'FM...' or 'BECMG' or, if no 'FM' or ‘BECMG' is given, up to the end of the validity period of the TREND, the prevailing weather conditions forecast in the METAR should be applied.

(c)Following FM (alone) or BECMG AT, any specified change should be applied from the time of the change.

(d)Following BECMG (alone), BECMG FM, BECMG TL, BECMG FM TL:

(1)in the case of deterioration, any specified change should be applied from the start of the change; and

(2)in the case of improvement, any specified change should be applied from the end of the change.

(e)In a period indicated by TEMPO (alone), TEMPO FM, TEMPO TL, TEMPO FM TL, PROB30/40 (alone):

(1)deteriorations associated with persistent conditions in connection with e.g. haze, mist, fog, dust/sandstorm, continuous precipitation should be applied;

(2)deteriorations associated with transient/showery conditions in connection with short-lived weather phenomena, e.g. thunderstorms, showers may be ignored; and

(3)improvements should in all cases be disregarded.

(f)In a period indicated by PROB30/40 TEMPO:

(1)deteriorations may be disregarded; and

(2)improvements should be disregarded. Note: Abbreviations used in the context of this AMC are as follows: FM: from BECMG: becoming AT: at TL: till TEMPO: temporarily PROB: probability

CONTINUATION OF A FLIGHT In the case of in-flight re-planning, continuation of a flight refers to the point from which a revised flight plan applies.

EVALUATION OF METEOROLOGICAL CONDITIONS It is recommended that the pilot-in-command carefully evaluates the available meteorological information relevant to the proposed flight, such as applicable surface observations, winds, temperatures aloft, terminal and area forecasts, air meteorological information reports (AIRMETs), significant meteorological information (SIGMET) and pilot reports. The ultimate decision whether, when, and where to make the flight rests with the pilot-in-command. The pilot-in-command also should continue to re-evaluate changing weather conditions.