Present weather is given using the codes listed on page 2. Appropriate intensity indicators and letter abbreviations will be combined in groups of two to nine characters to indicate present weather at, or in the vicinity of, the aerodrome.
If more than one form of precipitation is observed, the appropriate letter abbreviations shall be combined in a single group with the first being the dominant type of precipitation. In such a group, the intensity shall refer to the total precipitation. The qualifier VC will be used to report certain significant weather phenomena in the vicinity of the aerodrome Note: vicinity, for meteorological purposes refers to the area between approximately 8—16 km of an aerodrome reference point.
Pilots should exercise caution when interpreting automated present weather information, as it may not be equivalent to a human observation. Cloud height is reported in hundreds of feet using three figures, for example: ft is reported as Cloud amount is given using the following abbreviations listed on page 2.
In a weather report, nil cloud is reported as SKC sky clear. In a weather forecast, cloud information is not included if the sky is clear. Cloud information is given from the lowest to the highest layer or mass in accordance with the following criteria:.
Type of cloud is identified only for cumulonimbus and towering cumulus observed at or near the aerodrome. When an individual layer or mass of cloud is composed of cumulonimbus and towering cumulus with a common cloud base, the type of cloud is reported as cumulonimbus only, and the amount shall be reported as the sum of the CB and TCU amounts.
Whenever cumulonimbus cloud is forecast, the degree of associated thunderstorm activity or probability of occurrence is included. A clear sky will be indicated in a report by SKC. When the sky is obscured, the cloud group is omitted and vertical visibility may be given in the format VVhhh, where hhh is the vertical visibility in hundreds of feet. CAVOK is included in reports from staffed stations only or forecasts when the following conditions are observed, or forecast to occur, simultaneously:.
A report from an AWS with a cloud sensor will include data from this sensor in the body of the report if the report is fully automated in which case the abbreviation AUTO is also included in the message.
The data will be in the same form as manual reports except that:. Pilots should exercise caution when interpreting automated cloud information as it may not be equivalent to a human observation because:. These relate to improvements as well as deteriorations. FM is used when changes are expected at a specified time and which are rapid, BECMG is used when changes are expected to be regular or irregular to occur during the specified period.
When thunderstorms or reduced visibility due to fog, mist, dust, smoke or sand is forecast, but the probability is assessed at between 30 per cent and 40 per cent, the terms PROB30 or PROB40 are used.
If greater than, or equal to, 50 per cent probability is forecast, reference is made to the phenomenon in the forecast itself and not by the addition of a PROB statement. If a TAF includes a forecast of turbulence, its commencement will be indicated by the abbreviation FM, and its cessation within the forecast coverage will be indicated by the abbreviation TILL. Start and finish times are given in the format ddhhmm day of month, hour, minute.
Aerodrome weather reports contain both air temperature and dew point. Users should use linear interpolation to determine the forecast value between these points. The temperature forecasts are prefixed by the letter T. Negative values are indicated by the letter M before the numeral. Observed intermediate values are rounded down, for example: QNH is always given, prefixed by the letter Q , for example: Q The QNH forecasts are prefixed by the letter Q. The remarks section of the report will include rainfall recorded by an automatic rain gauge.
The information is in the form RF. Both amounts are expressed in millimetres to the nearest 0. Any other significant weather conditions for example an approaching front or visible bushfires are appended in plain language. When the visibility is expected to be greater than 6 statute miles, it is indicated as P6SM. A forecast visibility that is expected to vary between 2 and 4 statute miles with light rain showers would be indicated as:.
Weather and Obstructions to Vision : Forecast weather is always included immediately after the visibility. Obstructions to vision are only mentioned when the visibility is forecast to be 6 statute miles or less. A dashed line is used to enclose areas of intermittent or showery precipitation. A solid line is used to enclose areas of continuous precipitation.
Isobars : Isobars, which are lines joining points of equal surface pressure, are included in the GFA Clouds and Weather chart at 4 millibar intervals. Surface Winds : The speed and direction of forecast surface winds, with a sustained speed of at least 20 knots, are indicated by wind barbs and an associated wind speed value. Wind gusts are indicated by the letter "G", followed by the peak gust speed in knots. In the following example, the surface wind is forecast to be from the west o true with a speed of 25 knots and a peak gust speed of 35 knots.
The GFA Icing, Turbulence and Freezing Level chart depicts forecast areas of icing and turbulence as well as the expected freezing level at a specific time. Included on the chart are the type, intensity, bases and tops for each icing and turbulence area. Surface synoptic features such as fronts and pressure centres are also shown. This chart is to be used in conjunction with the associated GFA Clouds and Weather chart issued for the same valid period. Icing : Icing is depicted whenever moderate or severe icing is forecast for the coverage area.
The bases and tops of each icing layer, measured in hundreds of feet above mean sea level, as well as the type of icing e. Areas of light icing are described in the Comments Box. An area of moderate mixed icing, based at ft. ASL with a top of ft. ASL would be indicted as follows:. If icing is expected to be present during only part of the forecast period covered by the chart, the time of occurrence of the icing is indicated in the Comments Box.
Turbulence : Turbulence is depicted whenever moderate or severe turbulence is forecast for the coverage area. The base and top of each turbulence layer is measured in hundreds of feet ASL.
The height of the freezing level is measured above sea level and the contour lines for the freezing level will be at foot intervals, starting at the surface. But two months from now, Area Forecasts FA are gone for good. Now would be a good time to get used to their replacement: the Graphical Area forecast. The FA is a jumbled group of weather contractions, along with different effective times for the synopsis, VFR clouds and weather, and the outlook.
The hard-to-read format originated in the s, when character-count limitations required short hand format. Along with that, extremely large geographical areas covered in the forecast meant broad forecasts with limited value. Like a bad comic book villain, Area Forecasts aren't completely dead. Good Riddance, Except While Area Forecasts aren't anyone's favorite weather product, there is one thing that IFR pilots are going to miss: cloud top forecasts. Until recently, the Area Forecast was the only weather product with cloud top forecasts.
And for an IFR pilot flying in the mid-altitudes, those cloud-top forecasts are a big deal. Sure, there are PIREPs reported during the busiest flying hours of the day, but even those can be hard to come by in the less-traveled parts of the US. And having a solid plan to get out of icing conditions is critical for turbo-piston and turboprop pilots. The new cloud top forecasts are computer model generated, and they're almost completely automated.
When it comes to a gray stratus-cloud type of day, it works pretty well. But when you're dealing with a humid, convective day the type of day you'd expect to see a lot of ice , things get a little iffy. The same is true around frontal systems.
In the old forecast, input from human forecasters helped fix the cloud-top problem areas. In the new system, that isn't the case, because computers are doing nearly all the work.
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