Analysis of Intraseasonal Variability and Predictability of Atmospheric Processes of Regional Scale in the Northern Hemisphere Midlatitudes

Issues related to the intraseasonal variability and predictability of the atmospheric processes of a regional scale in the Northern Hemisphere are considered. To identify the latter, the circulation indices characterizing the large-scale modes of the atmospheric variability are used. An assessment of the regional intraseasonal variability of the atmospheric processes in the summer and winter seasons of 1991–2020 is given. A study of the practical predictability of the regional atmospheric processes is carried out using the global semi-Lagrangian model developed at the Marchuk Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS), jointly with the Hydrometeorological Center of Russia, as well as the reanalysis of the European Center for Medium-Range Weather Forecasts on a weekly and monthly time scales. It is concluded that, beyond of the first forecast week, the quality of deterministic (ensemble mean) forecasts drops sharply. In winter, the exception is the Pacific–North American oscillation region, where a useful signal is traced not only for the first prognostic week, but also for the second one. The use of the probabilistic forecasts makes it possible to increase the time interval of predictability compared to the deterministic approach from 1 week to 1 month. The biggest errors are noted in the forecasts of the circulation regimes in the west of the North Atlantic and in the west of the northern part of the Pacific, in the regions of the most significant intraseasonal variability. The results are supposed to be used in the operational practice of the intraseasonal forecasting of the North Eurasian Climate Center (NEACC).