Winter 2010 preliminary outlook for Europe

Fig. 1. Winter (DJF)2009/10 SAT forecast.

For the winter of 2009/10, seasonal temperatures are forecast to be above normal over much of northern and central Europe and near normal in southern Europe (Fig. 1). Note, however, that the CFs are relatively low, suggesting that deviations from the 1971-2000 average temperatures are not going to be very large.

The forecast from the IRI also calls for an anomalously warm winter in Europe, although the highest probabilities of positive temperature anomalies in their forecast are in southern Europe. In contrast, the CFS model output shows colder than normal temperatures almost everywhere, except Scandinavia and parts of eastern Europe.

Positive temperature anomalies in northern and central Europe are associated with the positive phase of the North Atlantic Oscillation (NAO), which is expected during the winter of 2009/10. The NAO forecast is based partly on the distribution of summer-fall SST anomalies in the North Atlantic, which appears to be conducive to an increased zonality in the winter atmospheric circulation pattern (rule 288). A predominantly zonal circulation is also expected due to El Niño (rule 73). The NAO index, however, will experience significant intra-seasonal variations, being positive in the early winter and turning negative in the late winter, so for the season as a whole, it will be only slightly positive.

Fig. 2. November 2009 SAT forecast.	Fig. 3. December 2009 SAT forecast.
Fig. 4. January 2010 SAT forecast.	Fig. 5. February 2010 SAT forecast.

In November–December, El Niño events are often associated with negative SLP anomalies extending from Hudson Bay to Scandinavia and positive SLP anomalies in the Azores high. This pattern suggests the presence of strong westerlies (i.e., a positive phase of the NAO) across the North Atlantic. The anomalies of the Aleutian and Iceland lows are in phase, with negative SLP anomalies in both areas. Temperature forecasts for November (Fig. 2) and December 2009 (Fig. 3) reflect the strong zonal circulation over the North Atlantic – European sector that will likely be prevalent in the early winter.

In January, the westerlies over the North Atlantic will start weakening. As a result, temperature anomalies over much of Europe will be close to average (Fig. 4). In February, the frequency of non-zonal weather types, characterized by a development of the Greenland anticyclone or the Atlantic ridge, will increase. The NAO index will become negative, and the temperature anomaly pattern in Europe will be almost opposite to that in the early winter. Negative temperature anomalies are forecast for Scandinavia and positive anomalies for the western Mediterranean.