Winter 2008 forecast for Europe - update

Summary: Although the winter of 2007-08 is forecast to be somewhat warmer than normal overall, significant swings in temperature are likely. Frequent cold spells are expected to occur at the beginning of the winter. The average November-December temperatures will be below normal over much of Europe, with the higher probability of this to happen in northern France and Great Britain. In January 2008, the atmospheric circulation will switch to more zonal types, which will bring warmer air from the North Atlantic. Anomalously warm conditions are expected in February 2008. Scandinavia has the highest confidence factor for a mild winter forecast. Colder than normal conditions are forecast for southern Europe. As for central Europe, the winter overall is expected to be close to normal, with below normal precipitation.

Fig. 1. Surface air temperature forecast for November-December 2007 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.

Fig. 2. Same as Fig. 1, except for Jan-Feb-Mar 2008.

Discussion

The forecast for the winter 2007-08 remains essentially the same (see our previous forecast): warmer than normal conditions in Scandinavia, colder than normal in the Mediterranean, and near normal in central Europe. This forthcoming winter, however, will likely be characterized by large intra-seasonal variations. It is expected to start on the cold side, with negative temperature anomalies over much of West Europe (Fig. 1). The analysis of the August-September sea surface temperature (SST) anomalies in the North Atlantic reveals a tendency to form a pattern that is conducive to an anomalously low pressure center over the eastern North Atlantic and above normal pressure in the higher latitudes (rule 288). This pattern translates into colder than normal temperatures over central and eastern Europe.

Since the North Atlantic Oscillation (NAO) index for the winter as a whole is forecast to be near zero (see the forecast for the North Atlantic), the effect of the ENSO on Europe will be more pronounced (strong positive or negative phase of the NAO usually masks the ENSO effect). During cold ENSO events, the November-December atmospheric circulation over the North Atlantic – European region tends to be characterized by frequent blocking of the mean zonal flow (rule 372). As a result, colder than normal weather will dominate over much of Europe.

In January 2008, the atmospheric circulation is expected to switch to a more zonal weather regime. This is suggested by rule 37 that links January temperature in central England with the strength and position of the circumpolar vortex in the preceding month of October. The zonal atmospheric circulation will intensify even further in February. Another possible circulation pattern in that month (as suggested by rule 382 will be the Atlantic Ridge weather regime, which features a positive sea level pressure (SLP) anomaly over the central North Atlantic and a negative anomaly over northern and central Europe. The main storm track will be shifted north of its normal position (rule 205), which will primarily affect Scandinavia, where temperature will be unseasonably mild. Over central Europe, the anticyclonic weather will probably continue to dominate (rule 73).

Overall, the winter of 2007-08, and particularly January through March (Fig. 2), will likely be warmer than normal in northern Europe, although not as warm as the previous winter. Colder than normal temperatures are forecast for southern Europe. Also, this winter is expected to be drier than normal in central Europe.