Relationship of ENSO to snowfall and related cyclone activity in the contiguous United States

The relationship of the El Nino-Southern Oscillation to the contiguous U.S, snowfall was investigated using data from 3841 cooperative observer stations for the period 1951-1997. Snowfall for seven strong El Nino and five strong La Nina events was compared with snowfall occurring during the other 34 winters. The average snowfall for the seven El Nino winters exhibits a coherent large-scale pattern with below-average snowfall across approximately the northern half of the United States and above-average snowfall over the southwestern United States. Application of the t-test indicates that these snowfall anomalies are significantly different (at the 10% level) from the base period snowfall in parts of the mid-Mississippi River basin, the northern Ohio River basin, the western Great Lakes, and the northwestern United States. During strong La Nina winters, above-normal snowfall occurs in the northwest United States and northern Great Lakes. Although these anomalies do not pass tests of statistical significance (at the 10% level), the difference between La Nina and El Nino years is quite notable in the northwest United States. The results suggest that useful long-range outlooks of snowfall anomalies are possible for certain areas of the contiguous United States during strong El Nino events. An analysis of the frequency of strong cyclones (central pressure <992 hPa) shows that the El Nino winters were characterized by above-normal frequency in the extreme southern United States and below-normal frequency along the U.S.-Canadian border, with the pattern approximately reversed in the La Nina winters.