European Seasonal Outlook
	WSI’s Energy group recently issued its European Seasonal Outlook for the 2003 – 2004 winter season The group utilizes a variety of high-tech tools to create the winter seasonal forecast.
These tools include a Climate Model, and two Statistical Model Forecasts, all run in-house. They also study sea surface temperature (SST) anomalies, snow cover characteristics during the early season, and prediction of the North American Oscillation (NAO). For the period of December 2003 through February 2004, the outlook is for a slightly colder-than-normal winter in all of Scandinavia, with the largest negative temperature anomalies in northern Scandinavia. Higher-than-normal temperatures are expected in all of mainland Europe, the UK, and Iberia. The largest positive temperature anomalies are expected in Iberia. For the period of January through March 2004, the outlook is for a colder-than-normal period in northern and central Scandinavia, with the largest negative temperature anomalies in northern Scandinavia. Higher-than-normal temperatures are expected in extreme southern Scandinavia, all of mainland Europe and the UK, as well as Iberia. The largest positive temperature anomalies are again expected in Iberia
DETAILED FORECAST DISCUSSION After a very cool October, the warmth has returned to most of Europe in November (below, right) as a very strong upper-air ridge has dominated for most of the month. This pattern was well predicted by our October forecast (below, left) with the warmest temperatures (relative to normal) in northern Scandinavia and the UK and the coolest temperatures (relative to normal) in northern mainland Europe. This relatively warm pattern is slowly breaking as the warmest temperatures slide off to the east, and a return to more seasonal temperatures is expected for much of the remainder of the month. This marks the beginning of another pattern change, which will likely bring much cooler weather to many parts of Europe in December. The dominant atmospheric phenomenon in European winters is the North Atlantic Oscillation (NAO). When the NAO is in the positive phase, relatively warm and wet winters occur throughout much Scandinavia, UK, and northern mainland Europe. Negative NAO winters, on the other hand, are generally cold and dry. Our new statistical model, which we currently use only for predicting precipitation, is indicating a pattern strongly correlated with the negative phase of the NAO. In particular, another dry winter is indicated for Scandinavia. Conversely, the climate and statistical models that we use to predict temperature are now both suggesting a warmer-than-normal winter over much of Europe, which is usually associated with wetter-than-normal conditions. WSI Energycast forecast for November, made October 13 (left) and actual November temperature anomaly (right)
One of the main contributors to the hot European summer was the exceedingly warm ocean temperatures in and around Europe. The mid-October data revealed slightly warmer-than-normal waters in and around Europe. During the past month, these ocean temperatures have cooled further, relative to normal, and in fact, it is apparent that the oceans have cooled significantly in all of the waters surrounding Europe. These changes increase the chances for cooler-than-normal weather this winter. As part of the seasonal forecasting process, WSI runs the Community Climate Model (CCM) version 3.6 in-house twice a month on a high-speed suite of computers. The CCM, like all numerical models, is initialized with atmospheric and oceanic data before the run begins. Mathematical equations representing physical processes in the atmosphere, in the ocean, and on the land are then used to predict the future state of atmosphere for the following six months. The CCM is run with two different land-surface modules (LSMs). An LSM controls the transfer of heat and moisture between the vegetation/soil and the overlying atmosphere. In order to quantify the skill of the CCM, we have run the model in “hind cast” mode for 20 years for both LSMs. Based on the results of this long model run, we know where and when the model is or is not skillful for each of the two LSMs. The two LSMs each have their strengths and weaknesses, with one of the LSMs being more skillful in the warm season and the other in the cool season. Using this knowledge, WSI intelligently combines the output from both LSMs to optimize the skill of the seasonal forecast. For this 4-month forecast period, our climate models are predicting a continuation of the warmer-than-normal weather (below, right), with lower-than-normal temperatures generally confined to parts of eastern Scandinavia. The changes between the output from the November model run and the October model run are relatively small (see figure below). Climate model output for the December-February period from our October run (left) and our November run (right)
WSI also uses sophisticated statistical techniques to predict seasonal weather patterns. The output from one of these techniques (below) suggests a warm winter for all of Scandinavia, UK, and mainland Europe. Statistical model temperature output for the December-February period from our October run (left) and our November run (right)
The other statistical technique is used to predict precipitation only. The forecast for the winter is shown below, from both our October run (left) and our November run (right). Both runs are consistent in indicating a dry winter in Scandinavia and a wet winter in Iberia, which is characteristic of a negative NAO winter. Statistical model precipitation output for the December-February period from our October run (left) and our November run (right). Reds signify drier-than-normal and greens signify wetter-than-normal