Large asymmetrical temperature trends at Mount Wilson, California

We compiled and analyzed a daily time series of temperatures and precipitation totals from Mount Wilson, California from 1918 to 1998. Our results show a large decline in maximum temperature, no change or an upward trend in minimum temperature, and a substantial decline in the diurnal temperature range (DTR). The interannual variations in monthly maximum temperature and DTR are significantly correlated with monthly precipitation levels, sea-surface temperatures (SSTs) off the coast of Southern California, and the Southern Oscillation Index (SOI). El Nino periods and/or months with high SST anomalies tend to be wet with lower maximum temperatures and DTR while La Nina periods and/or months of lower SSTs are hotter and drier with higher DTR values. It is noteworthy that the SOI and SSTs have significant trends toward more El Nino-like conditions with higher SSTs off Southern California.