Several recent observational studies suggest that precipitation characteristics in many different regions of the globe have changed during the 20th century, confirming the results of modeling studies that suggest a likely manifestation of a rise in global temperatures would be an enhancement of the hydrologic cycle. Such an enhancement of the global water cycle might result in an increase in the rates of evaporation and precipitation as well as an increase in the frequency of extreme precipitation events. Precipitation is produced by a complex combination of interacting processes operating over a wide range of space and time scales. Significant diurnal and synoptic variability is modulated on subseasonal timescales by a 22 day traveling wave and the 30-60 day Madden-Julian Oscillation and on interannual timescales by teleconnection patterns such as ENSO and the NAO which themselves may be modulated on much longer timescales. Because an anthropogenic signal is expected to project onto natural modes of climate variability, it is necessary to quantify the fluctuations associated with natural modes of variability across all relevant time scales. We use 50 years of gridded hourly and daily precipitation data over the United States to isolate and quantify the dominant changes in intraseasonal precipitation characteristics associated with ENSO events and to estimate the significance of the changes given the large amount of year-to-year variability in precipitation and the large event-to-event variability in ENSO. We then apply the discrete wavelet transform to decompose the precipitation time series into components containing variability on time scales ranging from a few hours to less than a season and evaluate scale-dependencies in the response of precipitation regimes in the United States to the onset of an ENSO event.