A storm is coming. None of us have ever experienced a storm like this. It could arrive very soon. But, as anyone who makes a living as a forecaster will quickly say, "On the other hand . . ." The storm is, of course, an influenza pandemic. Much has been written in the past few years about the virus known as H5N1 and its potential to develop into a pandemic. Some in the scientific community are questioning whether that will ever happen. If H5N1 does become pandemic, we have no basis for predicting whether it will be this year or 10 years from now. After all, H5N1 was first identified in birds in 1961; the first human cases did not appear until 1997.