* Satellites in space snap pictures of cloud cover and experts study them to judge how much rain they hold by how wide, how light, and how high they appear.
* US Landsat satellite cameras measure ''biomass'' - green plant growth on the land below - with infrared close-ups.
* Meteorologists draw wavy lines on charts and plot the Intertropical Convergence Zone, where moist ocean air meets desert currents and monsoons emerge or fade. . . .
But no one has yet come up with an accurate way to predict drought far enough ahead to permit quick and effective advance aid. Meteorologists say they can still predict weather with any certainty only 48 hours ahead.
Meanwhile: The National Oceanic and Atmospheric Administration (NOAA) in Washington sends out monthly rainfall and biomass bulletins to US embassies in Africa after studying satellite and other reports.
The Food and Agriculture Organization (FAO) in Rome pulls in images from the European Meteosat with a special dish antenna paid for by the Italian government. The Dutch government is financing a three-year plan to improve projections. A number of third-world countries have their own early-warning systems for drought, based mainly on assessing rainfall patterns and crops planted.
Among their difficulties: insufficient, inaccurate 10-day rainfall data in areas where there is no one to collect it.
Among countries with good records: Bangladesh and Cuba.
Do these two have lessons for Africa? Yes, according to Peter Cutler at the International Disaster Institute, Department of Human Nutrition, London School of Hygiene and Tropical Medicine.
At a conference in Nazareth, Ethiopia, in August, Mr. Cutler said Bangladesh was able to cope with famines in 1979 and 1981 by closely watching the price of coarse rice beforehand (shortages make the price rise) and by monitoring stocks of grain from which the government gives supplementary monthly rations to Army, police, and other civil servants. When the stock fell below three months' supply (600,000 tons), the government made emergency commercial purchases, and donors were alerted to an imminent need. The lesson for Ethiopia: Keep good stocks, keep good records, and work closely with donors.