Grid point wind and temperature (GPWT) forecasts
Grid point wind and temperature (GPWT) forecasts AIP GEN 3.5
GPWT charts provide a display of wind and temperature data derived from weather model data. The high-level and mid-level charts are produced with a 2.5° or 5° latitude and longitude grid resolution using data from the world area forecast system (WAFS) models.
The low level charts are produced with a 1.5° or 5° latitude and longitude grid resolution using data from the Bureau of Meteorology’s numerical weather prediction model. The data is overlaid on a geographic background. The values given represent the wind and temperature at a specific pressure level, which is approximated to a height or flight level, for the mid-point of each square.
GPWT are presented to aircrew on a geographic background to facilitate interpretation on specific routes.
A block of GPWT data contains the following information for each level:
- dd: two numbers indicating the wind direction in degrees true to the nearest 10
- fff: three numbers indicating the wind speed in knots
- t: the sign of the temperature (+ or -)
- TT: two numbers indicating the temperature in whole degrees celsius. Dashed line (– — —) are used when the grid point is below ground level and hence there is no valid wind or temperature for that point.
GPWT forecasts are issued every six hours. High-level and midlevel charts are valid in six hourly time steps for the next 24 hours, however, low level charts are valid in three hourly time
steps for the next 24 hours.
Receipt of a forecast for a particular validity time will automatically amend and supersede any prior issue for that time. Both issue and validity times appear with each forecast.