Winter 2009 forecast for Europe - update

Summary: Due to a significant revision of our forecast for the North Atlantic, the previous forecast for Europe has also been revised. Positive temperature anomalies are now expected in Scandinavia and negative anomalies in the Mediterranean region.

Fig. 1. Surface air temperature forecast for the winter (DJF) of 2009 in Europe. The blue (red) contours and the letter C (W) indicate colder (warmer) than normal temperatures. CL means near normal. The base period for calculating anomalies is 1971-2000. The numbers at the contours are confidence factors of the forecast.

Discussion

Since the forecast for Europe is largely determined by the phase of the North Atlantic Oscillation (NAO), the change in the forecast of the NAO (from a negative to positive phase) translates into a greater chance of warmer than average winter in Scandinavia and colder than average winter in the Mediterranean. The situation, however, appears to be more complicated, since it may not be a classical NAO pattern, but rather the so-called Equatorward displaced NAO (ED_NAO) pattern (van den Dool et al., 2007). In its negative phase, the ED_NAO pattern is characterized by a high pressure center in the 45-55°N latitudinal belt. The longitudinal position of the center within this belt is very important in determining the distribution of SAT anomalies over Europe. If the center is positioned close enough to Europe, then much of western Europe will be warmer than average. If the center is shifted west, toward the central North Atlantic, then southwestern Europe will likely be colder than average. So far, the forecast for Madrid suggests that winter SAT anomaly there will likely be negative.