Geophys. Res. Lett. doi:10.1029/2008GL034828 (2008)

Climate models predict that as Earth warms, the Northern Annular Mode (NAM), a flip-flopping pattern of climate variability in the Northern Hemisphere, will flop more firmly to its low-pressure-near-the-pole state.

By studying climate records, Stephanie McAfee and Joellen Russell of the University of Arizona in Tucson have shown what this means for spring weather in the southwestern United States — spring weather being particularly sensitive to the NAM's behaviour. An intensified NAM leads to warm weather coming earlier, shortening the winter rainy season and leading to drier weather that year. Their findings agree with work on changes in the path of the jet stream, and thus in the tracks that storms follow. Broadly speaking, more storms tracking further to the north mean less rain in the south.