Unusually weak stratospheric polar vortex helps to predict severe cold spells

It is well known that severe cold spells over Northern Eurasia and, in particular, in Finland, often occur following weak stratospheric polar vortex conditions. It is less known whether stratospheric polar vortex conditions affect predictability of such cold spells.

Predicting weather beyond one week is difficult. However, forecast models can, under certain conditions, predict increased probability of cold spells at lead times of 2-4 weeks. The article showed that at these lead times a forecast model predicts a threefold increase in probability of observed cold spell 3-5 days earlier under conditions when stratospheric polar vortex at 30-kilometer altitude is unusually weak in comparison to the cases when the polar vortex is strong. The result improve understanding of atmospheric predictability and can be used for developing early warning systems. Severe cold spells increase energy demand and lead to increased mortality. Therefore, predicting such events in advance helps economy and can potentially save lives.

The research is based on forecasts by the European Centre for Medium Range Weather Forecasts (ECMWF), reanalysis data, and statistical forecasts for the winter (November-March) seasons 1995-2020.

Further information:

PhD student Irina Statnaia, Finnish Meteorological Institute, irina.statnaya@fmi.fi

Research Professor Alexey Karpechko, Finnish Meteorological Institute, alexey.karpechko@fmi.fi

Scientific article is available on Quarterly Journal of the Royal Meteorological Society.

Reference: Statnaia, I., Karpechko, A., Kämäräinen, M. & Järvinen, H.(2022) Stratosphere–troposphere coupling enhances subseasonal predictability of Northern Eurasian cold spells. Quarterly Journal of the Royal Meteorological Society, 1– 15. Available from: https://doi.org/10.1002/qj.4335