$_{Figure 4-36.}$  VAD wind graphic. pressure altitudes. Wind direction is always in reference to  true north, and wind speed is given in knots. The temperature  is given in degrees Celsius; no winds are forecast when  a given level is within 1,500 feet of the station elevation.  Similarly, temperatures are not forecast for any station  within 2,500 feet of the station elevation. If the wind speed is  forecast to be greater than 100 knots but less than 199 knots,  the computer adds 50 to the direction and subtracts 100 from  the speed. A sample FD report is shown in  Figure 4-37 . times reports may be as small as 150 feet between altitudes.  Standard “wind barb” depictions are used to represent the  wind direction and speed at different altitudes. Plymouth State University in Plymouth, New Hampshire  operates a Weather Center with a website for locating VAD  winds. This user-friendly website offers pilots a convenient  selection of reporting stations at http://vortex.plymouth. edu/lnids_conus.html.  To decode this type of data group, the reverse process must  be accomplished. For example, when the data appears as  “731960,” subtract 50 from the 73 and add 100 to the 19;  the wind would be 230° at 119 knots with a temperature of  –60°C. If the wind speed is forecast to be 200 knots or greater,  the wind group is coded as 99 knots. When the data appears  as “7799,” subtract 50 from 77 and add 100 to 99; the wind  is 270° at 199 knots or greater. When the forecast wind speed  is calm or less than 5 knots, the data group is coded “9900,”  which means light and variable. METAR is an observation of current surface weather reported  in a standard international format. While the METAR code  has been adopted worldwide, each country is allowed to make  Observed weather condition reports are often used in the  creation of forecasts for the same area. A variety of different  forecast products are produced and designed to be used in  the preflight planning stage. Pilots need to be familiar with  the following printed forecasts: wind and temperature aloft  forecasts (FD reports), the terminal aerodrome forecast  (TAF), aviation area forecast (FA), and inflight weather  advisories (SIGMET, AIRMET). Wind and temperature aloft forecasts provide wind and  temperature forecasts for specific locations in the contiguous  United States, plus network locations in Hawaii and Alaska.  The forecasts are made twice a day based on the radiosonde  upper air observations taken at 0000Z and 1200Z. Up through  12,000 feet are true altitudes; at and above 18,000 feet are  4-36 Aviation Routine Weather Report (METAR) Wind and Temperature Aloft Forecast (FD Report)  Aviation Forecasts 