The deuterium/hydrogen ratios, expressed in terms of ΔD, of precipitation at Mohonk Lake, New York, from 118 individual storms during the six summers 1977--1982 have been measured and considered in light of the concurrent meteorological conditions. The so-called amount effect of Dansgaard-summers with above averge precipitation totals tend to have below average ΔD values is observed at Mohonk Lake and is also registered in the tree ring cellulose of water-stressed Eastern White Pine. A similar amount effect is also observed for individual events and can be explained in terms of differences between convective and cyclonic precipitation. Stable cyclonic precipitation has much lower ΔD values (-64.8) but much greater amounts (3.77 cm) on average than purely convective storms (ΔD=-27.2, 1.30 cm). The seasonal amount effect is related to the fact that during the 6-year observational period, wetter than normal summers at Mohonk Lake also had a higher than normal precentage of stable cyclonic precipitation and a lower than normal percentage of purely convective precipitation. ¿ American Geophysical Union 1987