By using the Southern Oscillation Index and identifying the twenty most negative and positive SOI years (re-centered on the mean of the entire dataset) from 1895-2009, and ESRL’s climate division composite page I decided to see if I could find some of the various frequently talked about El Nino/La Nina effects on the US. First, let’s have a look at temperatures.
El Nino is on the top, La Nina on the bottom. This more or less confirms some of the claims that El Nino leads to cooler weather in the southeast, although there are some differences in that the effect seems stronger in the western part of the South (the same for La Nina). Florida is notably warmer during El Nino’s than I’ve seen in other comparisons. So the relationship appears to show key differences, indicating that the link between El Nino and US weather may be less certain than sometimes portrayed.
With regard to Precipation:
El Nino appears to tend to be wetter in the South and Midwest, and drier area from the Mid-Atlantic to the Mississippi, with this pattern reversed in La Nina. I am unaware of what tends to be claimed for precipitation but notably many places in the US appear to have average precipitation in El Nino years and La Ninas, suggesting that little effect is present.