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the world, a~ I have already mentioned. In the central and southern Great Plains, for example, droughts develop when the high level winds are persistently strong in a west-east direction for a long period. Under these circumstances moisture-laden air of the Pacific is squeezed dryas it passes over the Rockies. Much of the moisture in this region is produced when warm, moist air from the Gulf of Mexico spills into the region and colli des with cold polar air moving down from Canada. When the west winds are strong, collisions of these two air masses occur farther east, leaving broad regions of the Great Plains abnormally dry. By the same token, strong west winds bring abnormally wet weather west of the Continental Divide. The air is wrung dryas it .rises over the mountains. " But the explanation is basically incomplete. We do not know why the persistent west winds occur. And reliable predictions will not be possible until we do. Weather studies show that severe droughts occurred in the central and southern Great Plains in the early 1950' s, but broke over most areas in the spring of 1957. They occurred also about 20 years before, in the famous "dust bowl" of the mid-1930's. Tree ring data suggest that severe droughts occurred many times in the past history of the Southwest, with several droughts usually occurr- ing in each century. Research to date has given us no certain clues to causes, and thus no real basis for forecasting the next severe drought. But there are hopeful signs of possible progress. And these I wish to review briefly. RECENT PROGRESS IN RESEARCH ON LARGE SCALE WEATHER PATTERNS. One suggestion to a possible cause of the Great Plains droughts of the 1930's and the 1950's is that these droughts came in years of very low activity of the sun. Can it be that changes in the sun affect the aver- age winds over the Rockies? If so, the whole story has not yet been unravelled. Low solar activity also prevailed in 1942-45 and in 1922-2~, but there were no comparable dust bowl conditions then. And there was apparently no general drought in the Great Plains 20 years before 1933, in the low solar activity period of 1910-14. If solar activity is respon- sible, we have not yet learned to measure the proper elements of this activity nor the way it works to alter the weather. A major effort in our work here at the High Altitude Observa- tory has been devoted to this problem of possible solar effects on the weather. This work, which has been almost entirely supported by private industry, suggests that short-term changes of sun emissions 6-