WEATHER FORECASTS FOR SALT AT THE SAAO (SUTHERLAND)
WEATHER FORECASTS FOR SALT AT THE SAAO (SUTHERLAND)
The first phase of developing Meteorological Forecasts for SALT was initiated in March, 2003. This phase had Setup and Maintenance of an Automated System for Operational Forecasts as its goal. The first version of the forecast programme was implemented in November, 2003 and a revised version in March, 2004. The final version (for Phase 1) became operational in July, 2004.
The forecasts are based on surface and upper-air output data from the regional Eta numerical meteorological model which is run by the South African Weather Service (SAWS). The Eta model is initialised twice daily at 00UT (02h00 SAST) and 12UT (14h00 SAST). The model runs are typically completed within 6 hours of initialisation. Data are then obtained by ftp. In the first version of the forecast programme (November, 2003), the forecasts were based only on standard level Eta model data at 50mb (hPa) vertical intervals interpolated to the altitude (1760m) of the Sutherland Observatory. These forecasts did not include the effects of the surface on temperature and relative humidity.
In March, 2004 a first attempt at forecasting the near surface (~ 15m) temperature and relative humidity was made. The final version (July, 2004) provides further improvement in the forecasts of near-surface temperature, relative humidity and dew point. Additionally, it utilises observations made at SAAO (Sutherland) in real-time to update the forecast in the afternoon hours so that the forecasts of temperature for sunset and the hours after sunset (targeting dome-open time) are improved further.
Each day the forecast is first made, typically, at 09h31 SAST. In the event that data from the SAWS arrives late, further attempts are made each hour thereafter till 15h31 SAST. The forecast is updated at 21h31 SAST using the output from the 12UT Eta model run. If input data are not received from the data provider a message is written to the forecast file indicating that a forecast could not be made. In addition to the forecast of hourly parameter values to 48 hours ahead, a detailed forecast of temperatures for sunset and the hours after sunset and a page containing severe weather advisories is produced. The forecast of temperatures for sunset and the hours after sunset is updated in the afternoon hours using surface observations from SAAO (Sutherland). Updating starts once the temperature maximum for the day has been reached.
A comparison of observations and forecasts based on the standard level Eta model data only has been completed for the period April-October, 2003. An evaluation of forecast accuracy using the final version is yet to be completed.