MET.TR.275 World area forecast centre responsibilities

(a)WAFCs shall use processed meteorological data in the form of grid point values for the supply of gridded global forecasts and forecasts of significant weather phenomena.

(b)For global gridded forecasts, WAFCs shall:

(1)prepare forecasts of:

(i)upper wind;

(ii)upper-air temperature;

(iii)humidity;

(iv)direction, speed and flight level of maximum wind;

(v)flight level and temperature of tropopause;

(vi)areas of cumulonimbus clouds;

(vii)icing;

(viii)turbulence;

(ix)geopotential altitude of flight levels; four times a day and be valid for fixed valid times at 6, 9, 12, 15, 18, 21, 24, 27, 30, 33 and 36 hours after the time (00.00, 06.00, 12.00 and 18.00 UTC) of the synoptic data on which the forecasts were based;

(2)issue forecasts referred to in point (1) and complete their dissemination as soon as technically feasible, but not later than 5 hours after standard time of observation;

(3)provide grid point forecasts in a regular grid comprising:

(i)wind data for flight levels 50 (850 hPa), 80 (750 hPa), 100 (700 hPa), 140 (600 hPa), 180 (500 hPa), 210 (450 hPa), 240 (400 hPa), 270 (350 hPa), 300 (300 hPa), 320 (275 hPa), 340 (250 hPa), 360 (225 hPa), 390 (200 hPa), 410 (175 hPa), 450 (150 hPa), 480 (125 hPa) and 530 (100 hPa) with a horizontal resolution of 1,25° of latitude and longitude;

(ii)temperature data for flight levels 50 (850 hPa), 80 (750 hPa), 100 (700 hPa), 140 (600 hPa), 180 (500 hPa), 210 (450 hPa), 240 (400 hPa), 270 (350 hPa), 300 (300 hPa), 320 (275 hPa), 340 (250 hPa), 360 (225 hPa), 390 (200 hPa), 410 (175 hPa), 450 (150 hPa), 480 (125 hPa) and 530 (100 hPa) with a horizontal resolution of 1,25° of latitude and longitude;

(iii)humidity data for flight levels 50 (850 hPa), 80 (750 hPa), 100 (700 hPa), 140 (600 hPa) and 180 (500 hPa) with a horizontal resolution of 1,25° of latitude and longitude;

(iv)geopotential altitude data for flight levels 50 (850 hPa), 80 (750 hPa), 100 (700 hPa), 140 (600 hPa), 180 (500 hPa), 210 (450 hPa), 240 (400 hPa), 270 (350 hPa), 300 (300 hPa), 320 (275 hPa), 340 (250 hPa), 360 (225 hPa), 390 (200 hPa), 410 (175 hPa), 450 (150 hPa) 480 (125 hPa) and 530 (100 hPa) with a horizontal resolution of 1,25° of latitude and longitude;

(v)direction, speed and flight level of maximum wind with a horizontal resolution of 1,25° of latitude and longitude;

(vi)flight level and temperature of tropopause with a horizontal resolution of 1,25° of latitude and longitude;

(vii)icing for layers centred at flight levels 60 (800 hPa), 100 (700 hPa), 140 (600 hPa), 180 (500 hPa), 240 (400 hPa) and 300 (300 hPa) with a horizontal resolution of 0,25° of latitude and longitude;

(viii)turbulence for layers centred at flight levels 100 (700 hPa), 140 (600 hPa), 180 (500 hPa), 240 (400 hPa), 270 (350 hPa), 300 (300 hPa), 340 (250 hPa), 390 (200 hPa) and 450 (150 hPa) with a horizontal resolution of 0,25° of latitude and longitude;

(ix)horizontal extent and flight levels of base and top of cumulonimbus clouds with a horizontal resolution of 0,25° of latitude and longitude.

(c)For global forecasts of en-route significant weather phenomena, WAFCs shall:

(1)prepare SIGWX forecasts four times a day and shall be valid for fixed valid times at 24 hours after the time (00.00, 06.00, 12.00 and 18.00 UTC) of the synoptic data on which the forecasts were based. The dissemination of each forecast shall be completed as soon as technically feasible, but not later than 7 hours after standard time of observation under normal operations and not later than 9 hours after standard time of observation during backup operations;

(2)issue SIGWX forecasts as high-level SIGWX forecasts for flight levels between 250 and 630;

(3)include in SIGWX forecasts the following items:

(i)tropical cyclone provided that the maximum of the 10-minute mean surface wind speed is expected to reach or exceed 34 kt;

(ii)severe squall lines;

(iii)moderate or severe turbulence (in cloud or clear air);

(iv)moderate or severe icing;

(v)widespread sandstorm/dust storm;

(vi)cumulonimbus clouds associated with thunderstorms and with points (i) to (v);

(vii)non-convective cloud areas associated with in-cloud moderate or severe turbulence and/or moderate or severe icing;

(viii)flight level of tropopause;

(ix)jet streams;

(x)information on the location of volcanic eruptions that are producing ash clouds of significance to aircraft operations, comprising: volcanic eruption symbol at the location of the volcano and, in a separate text box on the chart, the volcanic eruption symbol, the name of the volcano, if known, and the latitude/longitude of the eruption. In addition, the legend of SIGWX charts should indicate ‘CHECK SIGMET, ADVISORIES FOR TC AND VA, AND ASHTAM AND NOTAM FOR VA’;

(xi)information on the location of a release of radioactive materials into the atmosphere of significance to aircraft operations, comprising: the radioactive materials in the atmosphere symbol at the location of the release and, in a separate box on the chart, the radioactive materials in the atmosphere symbol, latitude/longitude of the site of the release and, if known, the name of the site of the radioactive source. In addition, the legend of SIGWX charts on which a release of radiation is indicated should contain ‘CHECK SIGMET AND NOTAM FOR RDOACT CLD’.

(4)The following criteria shall be applied for SIGWX forecasts:

(i)points (i) to (vi) of point (3) shall only be included if expected to occur between the lower and upper levels of the SIGWX forecast;

(ii)the abbreviation ‘CB’ shall only be included when it refers to the occurrence or expected occurrence of cumulonimbus clouds:

(A)affecting an area with a maximum spatial coverage of 50 % or more of the area concerned;

(B)along a line with little or no space between individual clouds; or

(C)embedded in cloud layers or concealed by haze;

(iii)the inclusion of ‘CB’ shall be understood to include all weather phenomena normally associated with cumulonimbus clouds, i.e. thunderstorm, moderate or severe icing, moderate or severe turbulence, and hail;

(iv)where a volcanic eruption or a release of radioactive materials into the atmosphere warrants the inclusion of the volcanic activity symbol or the radioactivity symbol in SIGWX forecasts, the symbols shall be included on SIGWX forecasts irrespective of the height to which the ash column or radioactive material is reported or expected to reach;

(v)in the case of coincident or the partial overlapping of points (i), (x) and (xi) of point (3), the highest priority shall be given to point (x), followed by points (xi) and (i). The point with the highest priority shall be placed at the location of the event, and an arrow shall be used to link the location of the other point(s) to its (their) associated symbol(s) or text box(es).

(d)Medium-level SIGWX forecasts for flight levels between 100 and 450 for limited geographical areas shall be issued.