North Atlantic Atmospheric Circulation and Jet Stream Variability: Links with summer and winter temperature and precipitation in north-west Europe and the UK, and a new seasonal forecasting method

Oral Presentation 

Variability in seasonal weather in north-west Europe is substantially determined by jet stream 
variability. The North Atlantic Oscillation (NAO) has been heavily studied as a key representation of 
this jet stream variability, but other circulation indices are also important. Here the first three 
principal component EOFs, which broadly correspond to the NAO, the East Atlantic pattern (EA) and 
Scandinavian pattern (SCA), as well as jet speed and latitude, are correlated with temperature and 
precipitation anomalies over Europe with a focus on north-west Europe, as well as measures of 
persistence and variability. In addition to single variate correlations, multiple correlation coefficients 
are also used to determine areas of significant correlation when combining two or three of the 
circulation indices. All three of the principal EOFs are significantly correlated with extreme high 
summer (July and August) temperatures in large areas of northern Europe. For much of north-west 
Europe, both winter temperatures and precipitation are positively correlated with the jet speed, and 
precipitation is negatively correlated with EOF3. A new method of seasonal weather forecasting is 
presented that uses complex machine learning methods to predict the three EOFs and to downscale 
these into probabilistic temperature and precipitation forecasts for the UK and for Europe, which 
has given promising early results. Improved seasonal forecasts, including persistence and variability, 
will be useful to a number of users, such as agri-food, transport, energy supply and insurance.