The magnitude and timing of spring snowmelt floods reflects seasonal snow accumulation and spring temperature patterns. Consequently, interannual variations in regions such as the intermountain West, with snowmelt annual maximum floods, may be related to low-frequency variations in winter/spring large-scale climate variability. Changes in the seasonality of basin precipitation and temperature consequent to slow changes in the baseline climate state (e.g., owing to natural climate variations and/or potential global warming trends) may have significant impacts on such floods. A case study of the Blacksmith Fork River in northern Utah that explores such a hypothesis is presented here. Trends and associations in the magnitude and timing of annual maximum floods are documented, their impact on time-varying estimates of the 100 year flood is assessed, and relationships with known large-scale, quasi-oscillatory patterns of climate variability are explored. Evidence for structured low-frequency variation in flood timing and magnitude and its relation to winter/spring precipitation and temperature and to tropical (El Ni¿o-Southern Oscillation) and extratropical (Pacific Decadal Oscillation) Pacific climate precursors is presented. Mechanisms for these ocean-atmosphere teleconnections to basin precipitation, temperature, and flood potential are discussed. ¿ 2000 American Geophysical Union