MANAIR Manual of Standards and Procedures for Aviation Forecasts: chapter 3
Chapter 3 Forecasts in digital form of the wind and temperature aloft
Forecasts in digital form of the winds and the temperatures aloft (FB) are prepared to meet aeronautical requirements for flight planning and to prepare documentation for flights in Canada and between Canada and the United States, Greenland, Mexico and the Caribbean. The FB wind and temperature forecasts are a replacement of the FD forecasts. However FD forecasts will remain available for a transitional period. The differences between the FD and FB forecasts include four issues per day instead of two; changes to the period of use and format changes in the headers.
3.2 Content and issuing offices
Objective forecasts of upper wind and temperature are issued by the Canadian Meteorological Centre (CMC) for the locations listed in Appendix B.
The CMC issues the FBCN31, FBCN33 and FBCN35 CWAO messages for the 3,000-foot; 6,000-foot; 9,000-foot; 12,000-foot and 18,000-foot levels above sea level (ASL). The 3,000-foot level is omitted when the terrain elevation is greater than 1,500 feet.
Note that the FB forecasts are based on a Numerical Weather Prediction (NWP) model. Because NWP models cannot fully resolve all terrain features, there can be, in areas of highly variable terrain (e.g. mountainous areas) instances of significant difference between actual and model station elevation. There are cases where the actual station elevation lies below 1,500 feet, but the model elevation for that station lies close to or above 3,000 feet. In such cases, the 3,000-foot forecasts are omitted. These cases are clearly noted in Appendix B.
Temperatures are never forecast for the 3,000-foot level.
The U.S. National Weather Service (NWS) issues objective forecasts of upper winds and temperatures for the same locations as the CMC, but for the 24,000-foot, 30,000-foot, 34,000-foot, 39,000-foot, 45,000-foot and 53,000-foot levels. These forecasts are transmitted under the headers FBCN31, FBCN33 and FBCN35 KWNO.
3.3 Issue times and periods of use
Wind and temperature forecasts in digital form (FB) are prepared four times daily and are based on 0000 UTC, 0600 UTC, 1200 UTC and 1800 UTC data, respectively. When FB are generated, 6, 12, 18, 24, 30 and 36-hour forecasts are created. The 6-hour, 12-hour and 24-hour forecasts become respectively the FBCN31, FBCN33 and FBCN35 messages, and are transmitted via the EC telecommunications network.
The 12-hour, 18-hour and 30-hour forecasts are kept as backups in case of computer problems in the subsequent forecast cycle. The 18-hour, 24-hour and 36-hour forecasts are also kept as back-ups; they are used when computer problems affect two consecutive forecast cycles.
Each of the 6-hour, 12-hour and 24-hour forecasts (or their backups when applicable), though valid for a particular time (denoted as “Valid Time”), applies to a specific period, called “Period of Use.” The following table gives the times of issue, the valid times and the periods of use of each forecast.
|Header||Observation time (UTC)||Approximate issue time (UTC)||Valid time (UTC)||Period of use (UTC)|
Note (1): Although their headers indicate a later time, the FBCN31, FBCN33 and FBCN35 CWAO forecasts are normally available on EC circuits towards 0300 UTC (forecasts based on 0000 UTC data), 0900 UTC (forecasts based on 0600 UTC data), 1500 UTC (forecasts based on 1200 UTC data) and 2100 UTC (forecasts based on 1800 UTC data).
Note (2): The headers in the FBCN31, FBCN33 and FBCN35 KWNO forecast bulletins generally indicate the issue time.
The symbolic form of the forecast is “ddfftt”, where dd is the wind direction in tens of degrees with respect to true north, ff is the wind speed in knots, and tt is the temperature in degrees Celsius.
Wind speeds from 100 KT to199 KT are indicated by subtracting 100 from the speed and adding 50 to the direction (e.g. 240 degrees at 130 KT is coded 7430). Speeds in excess of 199 KT are coded as if they were of 199 KT (e.g. winds from 90 degrees at 210 KT are coded 5999, as would winds of 199 KT). Finally, wind speeds less than five knots are indicated by 9900.
The sign of the temperature is indicated as plus “+” or minus “-”, for levels below 24,000 feet. Above 24,000 feet, the sign of the temperature is not indicated.
The CMC issues its regular FBCN bulletins in the following format:
FBCN31 CWAO 090320
DATA BASED ON 090000Z
VALID 090600Z FOR USE 0200-0900Z.
3000 6000 9000 12000 18000
YVR 2118 2322+04 2435+01 2447-08 2456-18
YYF 1818 2125+03 2136+01 2129-07 2134-19
The NWS issues its FBCN bulletins in the format of the following example:
FBCN31 KWNO 090158
DATA BASED ON 090000Z
VALID 090600Z FOR USE 0200-0900Z. TEMPS NEG ABV 24000 FT
24000 30000 34000 39000 45000 53000
YVR 0815-28 092043 081848 051249 331449 340653
YYF 1315-27 132043 132050 121151 280750 280652
Note: the FBCN KWNO bulletins contain an AWIPS header for internal NWS use on the second line of the forecast bulletin.
When an FB is issued based on a backup forecast (refer to 3.3), the first line of the FB is modified by adding the remark “COMPUTER INOPERATIVE ON DDTTTT DATA”, where DDTTTT represents the date and time of the data on which the FBCN31, FBCN33 and FBCN35 bulletins would have been based under normal circumstances (refer to the table in section 3.3).
Consequently, when a bulletin is based on backup forecasts, the CMC indicates the situation as shown in the following example:
FBCN31 CWAO 150320
COMPUTER INOPERATIVE ON 150000Z DATA
DATA BASED ON 141200Z
VALID 150600Z FOR USE 0200-0900Z.
3000 6000 9000 12000 18000
YVR 0608 0710-05 0419-07 0227-11 3641-18
YYF 0308 0411-07 0316-12 0225-15 0130-21
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